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DEPARTMENT OF THE INTERIOR 
 
 MONOGRAPHS 
 
 OF THE 
 
 United States Geological Survey 
 
 VOLUME LI 
 
 Part II.~PLA.TES 
 
 MM 2 1962 
 
 WASHINGTON 
 
 GOVERNMENT PRINTING OFFICE 
 1912 
 
UNITED STATES GEOLOGICAL SURVEY 
 
 (iEORGE OTIS SMITH, Director 
 
 /Ko^f 
 
 -7 /- 
 
 /At 
 
 CAMBRIAN BRACHIOPODA 
 
 BT 
 
 CHARLES D. WALCOTT 
 
 Part II.-I'L^TES 
 
 WASHINGTON 
 
 GOVERNMENT PRINTING OFFICE 
 1912 
 
PLATE I. 
 
PLATE I. 
 
 a. Area. s. Median septum (see flg. 47A, p. 567). 
 cl. Cardinal .scars. t. llidges mcnUoncd in the text (see flg. 
 
 h. Central muscle scar. 47A, p. 5<i7). 
 
 j. Anterior lateral muscle scars. t'. l)epres.sed cardinal area (see flg. 47A 
 n. Cast of short ridge in aiivance of apex. p. 5fi7). 
 
 p. Pedicle furrow. v. Visceral area. 
 
 RUSTELLA EDSONI Walcott (p. 327). 
 
 Figures 1 and la. Casts of the exterior of compres.sed ventral valves from Lotalily 25, Lower Cambrian, Georgia, 
 Vermont. IT. S. Nat. Mug. Cat. Nos. 51412a and 51412b, respectively. Specimens represented by figs. 
 1 and la were figured by Walcott [lS8Gb, PI. IX, figs. Ih and Ig, respectively; and 1891a. Tl. LXIX, 
 figs. Ih and Ig, respectively] as ventral \-alves of Kutorrjina rinf/iiUila. Figure 1 is the type. 
 
 lb. Cast of the interior of a ventral valve from Locahty 49a, Lower Cambrian, York, Pennsylvania. U. S. 
 Nat. Mus. Cat. No. 51463a. 
 
 Ic. Cast of the interior of a ventral valve from Locality 25, Lower Cambrian, Georgia, Vermont. U. S. Nat. 
 Mus. Cat. No. 51412c. 
 
 Id and le. Casts of the exterior of dorsal valves from Locality 392o, Vermont. U. S. Nat. Mus. Cat. No8. 
 52035a and 52035b, respectively. 
 
 CURTICIA ELEGANTULA Walcott (]). 369). 
 
 Figures 2, 2', 2". Top and back views and side outline of the exterior of a ventral valve, the type specijien. V. S. 
 
 Nat. Mus. Cat. No. 51902a. 
 2a, 2a', 2a". Top, side, and back views of a more nearly circular \entral valve than that represented by 
 
 fig. 2. U. S. Nat. Mus. Cat. No. 51902b. 
 2b. Top and side views of a ventral valve. V. S. Nat. Mus. Cat. No. 51902c. 
 
 2c. Partly exfoliated ventral valve showing inner layers of the shell. U. S. Nat. Mus. Cat. No. 51902d. 
 2d. Posterior view of an elevated ventral valve having a large delthyrium. U. S. Nat. Mus. Cat. No. 51902e. 
 2e. Posterior view of a ventral valve wdth very low delthyrium. L". S. Nat. Mus. Cat. No. 51902f. 
 2f. Back vie%v of the cast of a ventral valve. U. S. Nat. Mus. Cat. No. 51902g. 
 2g. Posterior portion of the cast of a ventral valve. U. S. Nat. Mus. Cat. No. 51902h. 
 2h, 2i, and 2]. Exterior of dorsal valves and side outlines. V. S. Nat. Mus. Cat. Nos. 51902i, 51902J, and 
 
 51902k, respectively. 
 2k. Interior of a dorsal valve with a trace of muscle scars near the apex. U. S. Nat. Mus. Cat. No. 51902 1. 
 21. Cast of the interior of a dorsal valve, retaining a portion of the .shell. L'. S. Nat. Mus. Cat. No. 51902m. 
 
 Another specimen (Cat. No. 51902n) was used also in drawing fig. 21. 
 
 The specimens represented are all from Locality 82b, I'pper Cambrian, ''St. Croix sandstone," Taylors Falls, 
 Chisago County, Minnesota. 
 
 Neobolus warthi Waagcn (p. 566). 
 
 [Te.xt figs. 47A-B, p. 567, and PI. LXXXI, figs. 2, 2a-h.] 
 
 Figure 3. This specimen is figured by Waagen [1885, PL LXXXIV, fig. 7; and 1891. PI. II, fig. 8c] as the interior 
 
 of a dorsal valve of Neobolus warlhi. It may possibly be an old shell, worn by rolling in the sand. 
 
 Geol. Survey India Cat. No. 3/779. 
 
 4 and 4'. Exterior and back views of a specimen of the ventral valve. Geol. Survey India Cat. No. 3/776. 
 
 Specimen figured by Waagen [1885, PI. LXXXIV, fig. 4; and 1891, PI. II, fig. 5] as Keobolus unrlhi. 
 
 4a. Specimen of the dorsal valve. Geol. Survey India Cat. No. 3/777. Specimen figured liy Waagen [1885, 
 
 PL LXXXIV, figs. 5a-b; and 1891, PI. II, figs. 8a-b] as Neobolus warlhi. ^ 
 4b. This figure, which is diagrammatic and incorrect, is replacedby text figure 47A, p. 567. Interior of a dorsal 
 valve from a cast made in a natural mold. Original in the collection of the Geological Survey of 
 India (Cat. No. 3/780); cast in the United Slates National Museum (Cat. No. 56909a). 
 5. Ventral valve described and illustrated by Waagen [1885, p. 759, PL LXXXV. figs, la-c: and 1891, 
 
 PL 11, figs, lla-b] as Neobolus vynnei. Geol. Survey India Cat. No. 3/781. 
 5a. Dorsal valve described and illustrated by Waagen [1885, p. 759, PL LXXXV, figs. 2a-<'; and 1891, 
 PL II, figs. lOa-b] as Neobolus injtviei. Geol. Survey India Cat. No. 3/782. 
 All the specimens from which the above figures of A'eoholus V'arlht are drawn are from Localitx' 357c. the A'eobolus 
 beds of the Khussak group of the Middle Cambrian, Kiura, Salt Range, India. 
 6 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. 1 
 
 .^^:^IF^^. 
 
 ^ A 
 
 FRANCES WIESER DEL. 
 
 LIOTVBE CO aCSICN 
 
PLATE I. 7 
 
 ScHizoPiiOLis RUGOSA Waagon (p. 609) . 
 
 [PI. LXXXI, fiRs. l,la-c.) 
 Figure 4c. Interior of a dorsal valve from a cast made in a natural mold. The casts were obtained first by dissolving 
 the shells and then taking wax and plaster casts of the uninjured natural molds. From Locality 
 357c, the Neohohis beds of the Khussak group of the Middle Cambrian, Kiura, Salt Range, India. 
 Original in the collection of the Geological Survey of India (Cat. No. 3/780); cast in the United States 
 National Museum (Cat. No. 56910a). 
 
 VOLBORTHIA RECURVA (Klltoi<;il) (j). 366). 
 
 [Textflss. 33A-B, p. 366.] 
 
 Figures 6, Ga, (jb, 6c, and Od. Posterior, side, front, ventral, and dorsal views of the type specimen, a partly 
 exfoliated shell which has the two valves united, from Locality 336g, Ordovician glauconitic lime- 
 stone at Zarskoe Selo, Government of St. Petersburg, Russia. 
 6e. View of the false area of the ventral yalve represented in fig.^. G, Oa-d. The false area of this shell haa 
 been illustrated by photography in text figs. 33A and 33B, j). 3GG. 
 
 Figures 6, 6a-e are copied from von Moller [1874, PI. VII, figs. 1-6, respectively]. Original specimen in the col- 
 lection of the Museum at Reval, Esthouia, Russia; cast in the United States National Museum (Cat. No. 58298). 
 
PLATE II. 
 
PLATE II. 
 
 MiCROMiTRA (Paterina) BELLA (Billings) (p. 344). 
 
 FiauRE 1. Apical, postorior, and fide views of a ventral valve. U. S. Nat. Mus. Cat. \o. 51417a. Until the speci- 
 men represented by fig. Ic is found this valve may be regarded as typical of the species. (See pp. 335 
 and 350 and fig. 6 of this plate.) 
 
 la. Summit, po.sterior, and side views of a dorsal valve. U. S. Nat. Mus. Cat. No. 51417b. 
 
 lb. Dorsal valve, showing a somewhat more elevated beak than in figure la. U. S. Nat. Mus. Cat. No. 51417c. 
 
 The specimens represented by figures 1, la-b are all from Locality 49w. Lower Cambrian limestone one-fourth 
 mile south of Emigsville, York County, Pennsylvania. 
 
 FiuuRE Ic. Type specimen, from Locality 2n, Lower Cambrian limestone bowlders in conglomerate at Trois Pistoles, 
 Quebec. Copied from Billings [lS72b, fig. 13, p. 477]. The figure has been widely copied (see p. 
 344), but the specimen from which it was drawn can not be located. (See pp. 335 and 350 and fig. 6 
 of this plate.) 
 
 MiCROMiTRA (Paterina) labradorica (Billings) (p. 347). 
 
 Figure 2. Enlarged drawing of the type specimen, from Locality 392a, Lower Cambrian at L'Anse au Loup, Straits 
 
 of Belleisle, Labrador. Geol. Survey Canada. Specimenoriginally figured by Billings [1861b, fig. 6, 
 
 p. 6]. 
 2a. Dorsal valve. U. S. Nat. Mus. Cat. No. 18309a. Specimen figured by Walcott [lS91a, PI. I.XIX, fig. 
 
 3b] as Kutorgina labradorica. 
 2b. Posterior view of a small ventral valve. V. S. Nat. Mus. Cat. No. 18309b. 
 2c. Partly exfoliated shell of a ventral valve. U. S. Nat. Mus. Cat. No. 18309c. Specimen figured by 
 
 Walcott [1891a, PI. LXIX, fig. 3a] as Kutorgina labradorica. 
 2d. A more elevated ventral valve, which has been partlj' broken away along the cardinal margin. U. S. 
 
 Nat. Mus. Cat. No. 18309d. Specimen figured by Walcott [1891a, PI. LXIX, fig. 3] as Kutorgina 
 
 labradorica. 
 
 The specimens represented by figures 2a-d are from Locality 41a, Lower Cambrian limestone at Topsail Head, 
 Conception Bay, Newfoundland. 
 
 Figure 2e. Dorsal valve from Locality 3a, Lower Cambrian shale, on Hanford Brook, St. John County, New Bruns- 
 wick, Canada. TT. S. Nat. Mus. Cat. No. 5142Sa. 
 2f. Ventral valve associated with specimen represented by figure 2e. V. S. Nat. Mus. Cat. No. 51428b. 
 
 MiCROMiTRA (Paterina) labradorica swantonensis (W'alcott) (p. 348). 
 
 Figure 3. Apical view and side outline of a ventral valve, the type specimen. U. S. Nat. Mus. Cat. No. 1.5329a. 
 3a. Apical view and side outline of a more elevated ventral valve. U. S. Nat. Mus. Cat. No. 15329b. 
 3b. Dorsal valve associated in the same block of limestone with the specimen represented by figure 3a. 
 U. S. Nat. Mus. Cat. No. 15329c. 
 
 The specimens represented by figures 3, 3a-b were figured by Walcott [1886b, PL IX, figs. 2, 2a-b, respectively] 
 as Kutorgina labradorica, and [1891a, PI. LXIX, figs. 2, 2a-b, respectively] as Kutorgina labradorica swantoneiisis. 
 
 Figure 3c. Longitudinal section of a ventral valve showing the presence of a .short iiseudodeltidium. U. S. Nat. 
 Mus. Cat. No. 1.5329d. 
 
 The specimens represented by figures 3, 3a-c are all from Locality 25a, Lower Cambrian limestones, 2 miles east 
 of Swanton, Franklin County, Vermont. 
 
 Figures 3d, 3e, and 3f. Apical, side, and posterior views of a specimen preserving the area and pseudodeltidium. 
 This specimen can not be located. The drawing was labeled as having been made from a specimen 
 in the collections of the American Museum of Natural History, but the officials inform me that they 
 have no record of such a specimen. The locality is unknown. 
 
 MiCROMiTRA (Paterina) prospectensis (Walcott) (p. 352). 
 
 Figure 4. Apical view of the type si>e(imen, a ventral valve, from Locality 82, Lower Cambrian sandy shales, summit 
 of Prospect Mountain. Eureka district, Nevada. 
 4a. Dorsal valve associated with the ventral ^■alve represented by figure 4. 
 
 The specimens represented by figures 4 and 4a were figured by Walcott [1884b, PI. IX, figs, la and 1. respectively; 
 1886b. PI. IX, figs. 3 and 3a, respectively; and 1891a, PI. LXIX. figs. 4 and 4a, respectively] as Kutorgina prospectensis. 
 V. S. Nat. Mus. Cat. Nos. 15335a and 1.5335b, respectively. 
 10 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. II 
 
 FRANCES WieSER DEL. 
 
 MCLioTvpe CO BOSTON 
 
PLATE IT. 11 
 
 MiCROMITRA ALABAMAENSIS (Walcott) (p. 337). 
 
 Figure 5. Apical view of the type specimen, a rcimpressed ventral valve, from Locality 121, Middle Cambrian Rogers- 
 ville shale, 4 miles northeast of Rosjersville, Tennessee. V. S. Nat. Mus. Cat. No. 51416a. Speci- 
 men figured by Walcott [lS97b, PI. LIX, fig. 5] as IphirJm (ilahdmnetisis. 
 
 5a. Dorsal valve from Locality 94a, Middle Cambrian Conasauga shale, Coosa \'alley, Cherokee County, 
 Alabama. U. S. Nat. Mus. Cat. No. 56888a. Specimen figured by Walcott [1897b, PI. LIX, fig. 5a] 
 as Iphidea alabamaensis. 
 
 5b. \'entral valve having a slight median depression, from Locality 14a, Middle Cambrian Rogersville shale, 
 4 miles north-northeast of Knoxville, Knox County, Tennessee. U. S. Nat. Mus. Cat. No. 51413a. 
 
 5c. Outer surface of .«hell from Locality 94, Middle Candjrian Conasauga shale, Cowan Creek section, Cherokee 
 County, Alabama, enlarged to show the tendency to form crenulations in the striae. U. S. Nat. Mus. 
 Cat. No. 26432a. This bit of surface was figured by Walcott [1897b, PI. LIX, fig. 5b] as part of the 
 surface of figure 5, magnified; it is, however, taken from another s]iecimen. 
 
 MiCEOMiTRA (Paterina) logani (Walcott) ([). 350). 
 
 Figures 6, 6a, and 6b. Apical, side, and posterior views of the type specimen, from Locality 2n, Lower Cambrian 
 pebbles in conglomerate at Trois Pistoles, on the St. Lawrence, Province of Quebec, Canada. Coll. 
 Geol. Survey Canada. Specimen figured by Walcott [lS97b, PI. LIX, figs. 2, 2a-b] as Iphidea logani. 
 In the Canadian Survey collections it was labeled as the type of '-Iphidea bella Billings." (See 
 pp. 345 and 3.50 and figs. 1 and Ic of this plate.) 
 
 MiCROMITRA (Paterina) supekba (Walcott) (p. 355). 
 
 (Text figs. 27A-B, p. 35.5.) 
 Figures 7, 7a, and 7b. Apical, side, and posterior views of the type specimen, a ventral valve, from Locality 73a, 
 
 Middle Cambrian sandy "Tonto" shale, Chuar Valley, Grand Canyon of the Colorado, Arizona. 
 
 U. S. Nat. Mus. Cat. No. 26429a. Specimen figured by Walcott [1897b, PI. LIX, figs, la-c] as Iphidea 
 
 superba. 
 7c. Specimen of the dorsal valve associated with the specimen represented by figure 7. L'. S. Nat. Mus. 
 
 Cat. No. 26429b. Specimen figured by Walcott [1897b, PI. LIX, fig. 1] as Iphidea superba. 
 7d. Nearly perfect dorsal valve from Locality 74, Middle Cambrian sandy •'Tonto" shale at head of Nunko- 
 
 weap Valley, Grand Canyon of the Colorado, Arizona. U. S. Nat. Mus. Cat. No. 51487a. 
 7e. Posterior view of ventral valve, from I>ocality 8j, Middle Cambrian shale, near Gordon Mountain, 
 
 Ovando quadrangle, Montana, showing pseudodeltidium. V. S. Nat. Mus. Cat. No. 51488a. 
 7f. A crushed and broken ventral valve, associated with the valve represented by figure 7e, showing pseudo- 
 deltidium. U. S. Nat. Mus. Cat. No. 5148Sb. 
 
 MiCROMITRA (Paterina) labradorica utahensis (Walcott) (p. 349). 
 
 [Text flg. 24, p. 350.] 
 
 Figures 8 and 8'. Summit and side A-iews of the tyi>e siiecimen, a ventral valve laterally compressed. V. S. Nat. 
 Mus. Cat. No. 51431a. 
 8a. Posterior half of a ventral valve somewhat distorted by compression. V . S. Nat. Mus. Cat. No. 51431b. 
 
 The specimens represented are both from Locality 3d, Middle Cambrian, Oquirrh Range, near Ophir, Utah. 
 
 Wimanella shelbtensis, Walcott (p. 747). 
 
 Figure 9. Type specimen, the ventral valye, flattened in the shale. Copied from Walcott [1908d, PI. X, fig. 3]. 
 9a. Interior of a flattened dorsal valve. 
 
 The specimens represented are both from Locality 17b, Lower Cambrian Rome (" Monte vallo") formation, 4 miles 
 south of Helena, Shelby County, Alabama. U. S. Nat. Mus. Cat. Nos. 52272a and .52272b, respectively. 
 
 MiCROMITRA (Paterina) williaudi Walcott (p. 358). 
 
 [Text figs. 30A-E, p. 3.58.1 
 Figures 9b and 9c. Side outlines of ventral valves. Drawn from casts taken in a natural mold from Locality 17b, 
 Lower Cambrian Rome (''Montevallo ") formation, 4 miles south of Helena, Shelby County, -Vlabama. 
 U. S. Nat. Mus. Cat. Nos. 51481a and 51481b, respectively. 
 
 MiCROMITRA xisus (Walcott) (p. 338). 
 
 Figure 10. Exterior of type specimen, ventral valve, from Locality 2r, Lcnver Cambrian, 2 miles west of Bic, Province 
 of Quebec, Canada, showing radiating ridges. V. S. Nat. Mus. Cat. No. 51440a. 
 
 MiCROMITRA (Paterina) labradorica orientalis (Walcott) (p. 348). 
 
 Figure 11. Exterior of type specimen, dorsal valve, from Locality C9, Middle Cambrian limestone, Kiulung group, 
 3 miles southwest of Yenchuang, Sintai district, Shantung, China. V. S. Nat. Mus. Cat. No. 52516a. 
 
PLATE III. 
 
 13 
 
PLATE III. 
 MiCROMiTRA (Paterina) stissingensis (Dwight) (p. 353). 
 
 FiGtJRE 1. Apioal view of the type specimen, a ventral valve. U. S. Nat. Mus. Cat. No. .51484a. Specimen figured 
 
 by Dwight [1889, PI. VI, tip;. G] as Kulorgina stissingensU. 
 la. Dorsal valve, flattened in the shale. U. S. Nat. Mus. Cat. No. 51484b. The rear view of this specimen 
 
 was given by Dwight [1889, PI. VI, fig. 8]. 
 lb. Apical \dew of a cast in limestone of a ventral valve. U. S. Nat. Mus. Cat. No. .51484c. 
 Ic. Interior of a typical specimen of a compressed dorsal valve. V . S. Nat. Mus. Cat No. 51484d. Specimen 
 
 figured by Dwight [1889, PI. VI, fig. 5] as Kutorgina stissingensis. 
 Id. Posterior view of a compressed ventral valve that shows the area of a narrow pseud odeltidium. 
 
 The specimens represented by figures 1, la-d are from Locality 367d, Middle Cambrian, vicinity of Stissing, 
 Dutchess County, New York. 
 
 Figure le. Specimen doubtfully referred to this species from Locality 14s, Middle Cambrian, Ogygopsis zone. Mount 
 Stephen, British Columbia. U. S. Nat. Mus. Cat. No. ol483a. 
 
 MiCROMiTKA pusiLLA (LinQarsson) (p. 339). 
 
 Figures 2 and 2a. Apical and posterior views of a ventral valve. U. S. Nat. Mus. Cat. No. ol478a. 
 2b and 2b'. Top and side views of a ventral valve. U. S. Nat. Mus. Cat. No. 5147Sb. 
 2c. Exterior of a dorsal valve. U. S. Nat. Mus. Cat. No. .51478c. 
 
 The specimens represented are all from Locality 8w, Middle Cambrian limestones near Andraruni, Sweden. 
 MiCROMITRA PEALEI (Walcott) (p. 339). 
 
 Figures 3, 3a, and 3b. Apical, side, and posterior views of the type specimen, from Locality 155a, Middle Cambrian 
 
 limestone near Hillsdale, Montana. U. S. Nat. Mus. Cat. No. 26430a. Specimen figured by Walcott 
 
 [1897b, PI. LIX. figs. 3, 3a-b] iis Iphidea pealei. 
 3c. Dorsal valve from the same bed of limestone as the ventral valve re])resented by figure 3. U. S. Nat. 
 
 Mus. Cat. No. 26430b. Specimen figured by Walcott [1897b. PI. LIX, fig. 3c] as Iphidea pealei. 
 3d. Ventral valve with strong radiating ridges, from Locality 159, Middle Cambrian limestone, north of West 
 
 Gallatin (Gallatin) River, Montana. U. S. Nat. Mus. Cat. No. 51471a, 
 3e and 3e'. Top and back views of a transverse dorsal valve with strong radiating ridges, from Locality 5f, 
 
 Middle Cambrian limestone, 12 miles south of Neihart, Montana. V. S. Nat. Mus. Cat. No. 51470a. 
 
 MiCROMITRA (Paterina) crenistria (Walcott) (p. 345). 
 
 Figures 4, 4a, and 4b. Apical, side, and posterior vifews of the type specimen, from Locality 74, Middle Cambrian 
 limestone, Tonto group, near the head of Nunkoweap A'alley, Grand Canyon of the Colorado, .Vrizona. 
 U. S. Nat. Mus. Cat. No. 26431a. Specimen figured by Walcott [lS97"b, PI. LIX, figs. 4, 4a-b] as 
 Iphidea crenistria. 
 
 MiCROMITRA SCLT-PTILIS (^leek) (p. 341). 
 
 Figures 5, 5', and 5". Apical, side, and posterior views of the type specimen, from Locality 302, Middle Cambrian 
 limestone east of West Gallatin (Gallatin) River, Montana. U. S. Nat. Mus. Cat. No. 7864a. Speci- 
 men figured by Walcott [1884b, PI. I, figs. 7, 7a] as Kutorgina sculplilis. 
 
 5a, 5a', and 5a". Top, side, and back views of a ventral valve from Locality 302b, Middle Cambrian lime- 
 stones near Crowfoot Ridge, Yellowstone National Park, Wyoming. U. S. Nat. Mus. Cat. No. 35212a. 
 Specimen figured by Walcott [1S99, ?1. I.X, figs. 5, 5a-c]. A portion of its surface is enlarged in 
 figure 5e. 
 
 5b. Dorsal valve from Locality 58, Middle Cambrian Secret Canyon shale, Eureka di.«trict, Nevada. U. S. 
 Nsit. .Mus. Cat. No. 24.551a. Specimen figured by Hall and Whitfield [1S77, PI. 1. fig. 1 1] as Kutorgina 
 minutissima; and by Walcott |18S4b, PL I, fig. 7b] as Kutorgina sculplilis. 
 
 5c. Dorsal valve associated with the shell represented by fig. ob. U. S. Nat. Mus. Cat. No. 245.Tlb. Specimen 
 figured by Hall and Whitfield [1877, PL I, fig. 12] as Kutorgina minutissima; and by Walcott [1884b, 
 PL IX, fig. 7] as Kutorgina sculplilis. 
 14 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. Ill 
 
 FRANCES WIESER DEL. 
 
 MELIOTVPe CO BOSTON 
 
PLATE III. 15 
 
 MiCROMiTRA SCT7LPTILIS (Meek) — Continued. 
 
 Figure 5d. Crushed ventral valve from Locality 8i, Middle Cambrian shaly Marjum limestone near Antelope Springs, 
 House Range, Utah. U. S. Nat. Mus. Cat. No. 51494a. 
 5e. A portion of the surface of the specimen represented by figure 5a, greatly enlarged. U. S. Nat. Mus. 
 Cat. No. 35212a. 
 
 MicROMiTRA (Iphidella) ornatella (Linnarsson) (p. 360). 
 
 Figures (i, 6a, and Gb. Apical, side, and posterior views of a typical specimen from Locality 320f, Middle Cambrian 
 
 limestone at Andrarum, Sweden. U. S. Nat. Mus. Cat. No. 26667a. 
 6c. Dorsal valve from Locality 8w, Middle Cambrian limestone near Andrarum, Sweden. U. S. Nat. Mus. 
 
 Cat. No. 51460a. 
 6d. Interior of a dorsal valve from Locality 16h, Middle Cambrian shale at Borregaard, Bornholm, Denmark. 
 
 U. S. Nat. Mus. Cat. No. 51490a. 
 
 MiCROMiTRA sjj. limit. (Walcott) (p. 343). 
 
 Figure 7. Dorsal valve from Locality 302b, Middle Cambrian limestones near Crowfoot Ridge, Yellowstone National 
 Park, Wyoming. U. S. Nat. Mus. Cat. No. 51509a. Specimen figured by Walcott [1899, PI. LX, 
 fig. 6] as "Iphidea, sp. undet." 
 
 MiCROMiTRA (Paterina) phillipsi (IIoll) (p. 351). 
 
 Figure 8. Top view of dorsal valve and side outline of valves from Locality 304g, Upper Cambrian Hollybush sand- 
 stones, Malvern Hills, England. Copied from Davidson [1866, PI. IV, figs. 17a and 17c]; Davidson's 
 figures were drawn from the type specimen illustrated by Holl [1865, p. 102, figs. 10b and 10c]. 
 
 MiCROMiTRA (Iphidella) nyssa Walcott (p. 360). 
 
 Figure 9. Top view of type specimen, a ventral valve. Copied from Walcott [1908d, PI. VII, fig. 5]. 
 9a. Top view of dorsal valve. 
 
 The specimens represented are both from Locality 4q, Middle Cambrian shale, near Gordon Mountain, Ovando 
 quadrangle, Montana. U. S. Nat. Mus. Cat. Nos. 51441a and 51441b, respectively. 
 
 MiCROMiTRA (Paterina) etheridgei (Tate) (p. 346). 
 
 Figure 10. Top view of type specimen, a ventral valve from Locality 315, Middle Cambrian at Curramulka, South 
 Australia. Original in the collection of the LTniversity of Adelaide, South .\ustralia; cast in the Ignited 
 States National Museum (Cat. No. 58301). Specimen figured by Tate [1892, PI. II, figs. 7a-c] as 
 Platyceras etheridgei. 
 
 10a and 10b. Side and back ^dews of ventral valve represented in figure 10. Original in the collection of 
 the University of Adelaide; cast in the United States National Museum (Cat. No. 58301). 
 
 10c. Back view of another ventral valve from the same locality as the valve represented by figure 10. Original 
 in the collection of the L'niversity of Adelaide; cast in the United States National Museum (Cat. No. 
 58302). 
 
PLATE IV 
 
 62667°— VOL 51, pt 2—12 2 17 
 
PLATE IV. 
 MiCROMiTKA (Iphidella) pannula (Wliite) (p. 361). 
 
 (Text fig. 32, p. 362, and PI. IV, figs. 3 and 3a. ] 
 
 Figures 1 and la. Apical and side views of a ventral valve from Locality 74, Middle Cambrian "Tonto" sandstone 
 
 Grand Canyon of the Ctilorado, Arizona. U. S. Nat. Mus. Cat. No. 51446a. 
 lb. Dorsal valve from Locality 149a, Middle Cambrian limestone on Pole Creek, Madi.s<in County, Montana. 
 
 U. S. Nat. Mus. Cat. No. 5144.5b. 
 Ic. Dorsal valve from Locality 14, Middle Cambrian limestone 7 miles southwest of Rome, Floyd County, 
 
 Georgia. U. S. Nat. Mus. Cat. No. 51444c. 
 Id and le. Posterior and side views of ventral valve from Locality 30, Lower Cambrian limestones near 
 
 Pioche, Nevada. U. S. Nat. Mus. Cat. No. 514.52a. Copied from Walcott [1908c, PI. I, figs, lb 
 
 and la, respectively.] The figures were there wrongly placed as the posterior and side views of the 
 
 specimen represented by figure Ir of this plate. The latter specimen occurs in British Columbia; 
 
 the one represented by figures Id and le occurs in Nevada. 
 If. Posterior view of the dorsal valve represented in figure lb, showing the characters described in the text 
 
 (see p. 362). U. S. Nat. Mus. Cat. No. 51445b. 
 Ig. Drawing of the type specimen of the species. Locality 31a, Lower Cambrian siliceous shale near Pioche, 
 
 Nevada. U. S. Nat. Mus. Cat. No. 1.5331a. Specimen figured by White [1877, PI. I, figs. 4a and 4b] 
 
 as Trematk pannula; and by Walcott [ISSGb, PL VII, figs. 3 and 3a; and lS91a, PI. LXIX, fig. 5d] as 
 
 Kutorgina pannula. The surface is enlarged in figure lo of this plate. 
 Ih and li. Apical and posterior views of a dorsal (?) valve from Locality 73a, Middle Cambrian "Tonto" 
 
 sandstone, Grand Canyon of the Colorado, Arizona. U. S. Nat. Mus. Cat. No. 51447a. The surface 
 
 is enlarged in figure In of this plate. 
 Ij and 1 1. Apical and side views of a small specimen from Locality 31a, Lower Cambrian limestone near 
 
 Pioche, Nevada. U. S. Nat. Mus. Cat. No. 15333a. Specimen figured by Walcott [188(ib, PI. VIII, 
 
 figs. 2 and 2a; 1801a, PI. LXIX, figs. 5 and 5a] as Kutorgina pannula. 
 Ik. Dorsal valve from same locality as the specimens represented by figures Ij and 1 1. U. S, Nat. Mus. 
 
 Cat. No. 15333b. Specimen figured by Walcott [1886b, PI. VIII, figs. 2b and 2c; 1887, PI. I, fig. 14b; 
 
 and 1891a, PI. LXIX, figs. 5b and 5e] as Kutorgina pannula. The outer surface is enlarged in figure 
 
 Ip of this plate. 
 Im. Ventral valve from Locality 38a, Lower Cambrian limestones near North Granville, Washington County, 
 
 New York. U. S. Nat. Mus. Cat. No. 17442a. Specimen figured by Walcott [1887, PI. I, figs. 14 and 
 
 14a; and 1891a, PI. LXIX, figs. 5c and 5f] as Kutorgina pannula. The outer surface is enlarged in 
 
 figure Iq of this plate. 
 In. Enlargement of a portion of the outer surface orthe specimen represented by figure Ih. 
 lo. Enlargement of a portion of the outer surface of the type specimen, figure Ig. 
 Ip. Enlargement of a portion of the outer surface of the specimen repre.«ente<l by figure Ik. Figured by 
 
 Walcott [1891a, PI. LXIX, fig. 5e] as the surface of the specimen represented by figure Im; and 
 
 [1887, PI. I, fig. 14b; and 1886b, PI. VIII, fig. 2c] as the outer surface of Ik. 
 Iq. Enlargement of a portion of the outer surface of the dorsal valve represented by figure Im. Figured by 
 
 Walcott [1891a, PI. LXIX, fig. 5f] as the surface of the valve represented by figure Ik; and [1887, PL 
 
 I, fig. 14a] as the outer surface of Im. 
 Ir. Ventral valve from Locality 14s, Middle Cambrian Ogygopsis zone on Mount Stephen, British Columbia. 
 
 Coll. Mr. Byron E. Walker, Toronto, Canada. Copied from Walcott [1908c, PI. I, fig. 1]; see note 
 
 under figures Id and le. 
 Is. Enlargement by photography of a ventral valve from Locality 74, Middle Cambrian ".Tonto" sandstone. 
 
 Grand Canyon of the Colorado, Arizona. U. S. Nat. Mus. Cat. No. 51446b. 
 It. Enlargement by photography of a ventral valve from Locality 149a, Middle Cambrian limestones on Pole 
 
 Creek, Madison County. Montana. IT. S. Nat. Mus. Cat. No. 51445a. 
 
 MiCROMITRA (IpHIDET.LA) PANNIILA MALADENSIS (Walcott) (p. 364). 
 
 Figure 2. Exterior of ventral valve from Locality Sb, Middle Cambrian limestone, 2 miles southeast of Malade, Idaho, 
 showing pitting of surface, and obscure, radiating ridges. IT. S. Nat. Mus. Cat. No. 51468a. 
 2a. Apical view of ventral valve associated with valve represented by figure 2. U. S. Nat. Mus. Cat. No. 
 51468b. 
 18 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. IV 
 
 MELioTvpe CO ecsTOH 
 
PLATE IV. 19 
 
 MiCROMITRA (IpIIIDELLA) PANNULA MALADENSIS (Walcott) C07)tilHl('(l. 
 
 Figures 2a' and 2a". Side aud back viows of specimen represented by figure 2a, illustrating the area and pseudodel- 
 tidium. 
 
 2b, 2b', and 2b". Apical, back, and side views of an elevated ventral valve from Locality 6g, Middle Cam- 
 brian limestone, Chappie Arm, Trinity Bay, Newfoundland. U. S. Nat. Mus. Cat. No. 51496a. 
 
 2c. Apical view of an elevated, laterally compressed ventral valve associated with the valve represented by 
 figure 2b. U. S. Nat. Mus. Cat. No. 51469b. 
 
 2d and 2e. E,\terior of two dorsal valves from Locality 5b, Middle Cambrian limestone, 2 miles southeast of 
 Malade, Idaho, with the same type of surface as the specimen rcjirescnted by figure 2. U. S. Nat. 
 Mus. Cat. Nos. 51468c and 5146Sd, respectively. Figure 2e represents the type specimen. 
 
 2f. Partly exfoliated, transverse dorsal valve from locality 6g, Middle Cambrian limestone, Chappie Arm, 
 Trinity Bay, Newfoundland. U. S. Nat. Mus. Cat. No. 51469c. 
 
 2g. Enlargement of a portion of the surface near the center of a ventral valve from Locality 61), Middle Cam- 
 brian limestone, 2 miles southeast of Malade, Idaho, that has (on its frontal portion) a surface like 
 that represented by figure 4c of the variety ophirensis. U. S. Nat. Mus. Cat. No. 51468e. 
 
 MiCROMITRA (IpIIIDELLA) PANNULA (White) (|). Sfil). 
 (Text fig. 32, p. 302, and PI. IV, figs. 1, la-t.] 
 
 Figure 3. Posterior portion of a ventral valve having a very fine surface of the type represented by figure Iq. 
 
 3a and 3a'. Apical and side views of a ventral valve associated with the specimen represented by figure 3. 
 
 The specimens represented are both from Locality 14, Middle Cambrian limestone, 7 miles southwest of Rome, 
 Floyd County, Georgia. U. S. Nat. Mus. Cat. Nos. 51444a and 51444b, respectively. 
 
 MiCROMITRA (IPIIIDELLA ) PANNULA OPHIRENSIS (Walfott) (p. .365). 
 
 Figures 4 and 4'. Apical and side views of a ventral valve. V. S. Nat. Mus. Cat. No. 51464a. 
 
 4a, 4a', and 4a". Apical, back, and side views of a ventral valve, the type specimen, in which the beak 
 slightly overhangs the posterior margin. U. S. Nat. Mus. Cat. No. 51464b. (See fig. 4c.) 
 
 4b. Exterior of a dorsal valve with very fine, undulating, concentric striae. U. S. Nat. Mus. Cat. No. 51464c. 
 
 4c. Enlargement of a portion of the specimen represented by figure 4a, to illustrate irregular and. inoscu- 
 lating stria;. U. S. Nat. Mus. Cat. No. 51464b. 
 
 4d and 4d'. Top and back views of a transverse dorsal valve. U. S. Nat. Mus. Cat. No. 51464d. 
 
 4e. Partly exfoliated dorsal valve, showing the cast of a median septum and the position of the central 
 muscle scars. U. S. Nat. Mus. Cat. No. 51464e. 
 
 4f. A small, convex dorsal valve. U. S. Nat. Mus. Cat. No. 51464f. 
 
 The specimens represented are all from Locality 3e, Middle Cambrian limestone, Oc{uirrh Range, near Ophir, Utah. 
 
PLATE V. 
 
 21 
 
PLATE V. 
 
 a. Pseudo-area. p. Pedicle opening, 
 
 h. Central mascle scar. s. Median septum, 
 
 j. Anterior lateral muscle scar. v. Visceral area. 
 
 vs. Main vascular sinus. 
 
 KuTORGiNA ciNGULATA (BilHngs) (p. 580). 
 
 (Text figs. 3, p. 299, 8, p. 29!l, and .WA-C, p. 581.) 
 
 Figure 1. Top and side \-iew of a partly exfoliated vontral valve from Locality 25a, liower Cambrian limestone, 2 
 
 miles ea.st of Swanton, Vermont. U. S. Nat. Mu.s. ('at. No. 15:i37a. Speeimeii figured by Waleott 
 
 [188eb, PI. IX, fig. Id; and 1891a, PI. LXIX, fig. Id], 
 la. Side view of the two valves united, from Locality 25a, near Swanton, Vermont. U. S. Nat. Mus. Cat. No. 
 
 15337b. Specimen figured by Walcolt [1886b, PI. IX, fig. Ic; and 1891a, PI. LXIX, fig. Ic]. 
 lb Ic, and Id. Side, ventral, and dorsal \-iews of a nearly entire shell, natural size, from Locality 26a, near 
 
 Swanton, Vermont. U. S. Nat. Mus. Cat. No. 15337d. Specimen figured by Waleott f 188Gb, PI. IX, 
 
 figs. 1, la-b; and 1891a, PI. LXIX, figs. 1, la-b]. 
 le and If. Side and dorsal \'iews of a younger shell than that represented by figures lb, Ic, and Id, but from 
 
 the same locality. V. S. Nat. Mus. Cat. No. 15336a. 
 Ig. E.xfoliated dorsal valvii, showing central muscle scars and radiating vascular canals. From Locality 
 
 392a, Lower Cambrian limestones at L'Anse au Loup, Labrador. L". S. Nat. Mus. Cat. No. 14893a. 
 Ih. Interior of a dorsal valve from Locality 25a, Lower Cambrian limestone, 2 miles east of Swanton, Vermont, 
 
 showing muscle scars and vascular canals. V. S. Nat. Mus. Cat. No. 15337c. Specimen figured by 
 
 Waleott [1886b, PI. IX, fig. If; and 1891a, PI. LXIX, fig. If]. 
 li. Exterior of a dorsal valve from Locality 26a, Lower Cambrian, 2 miles east of Swanton, Vermont. U. S. 
 
 Nat. Mus. Cat. No. 15337f. Specimen figured by Waleott [1886b, PI. IX, fig. le; and 1891a, PI. LXIX, 
 
 fig. le]. 
 Ij. Exterior and side views of a fine ventral valve from Locality 2o, Lower Cambrian limestone, Bic Harbor, 
 
 Pro\-ince of Quebec, Canada. U. S. Nat. Mus. Cat. No. 51510a. 
 Ik and Ik'. View of area and side view of a ventral valve from Bic Harbor (Locality 2o). U. S. Nat. Mus. 
 
 Cat. No. 51510b. 
 11 and Im. Exterior views of two dor.sal valves from Bic Harbor (Locality 2o). U. S. Nat. Mus. Cat. Nos. 
 
 51510c and 51510d, respectively. 
 In. Xiow of pseudo-area beneath apex of an elevated ventral valve from Locality 25a, Lower Cambrian lime- 
 stone, 2 miles east of Swanton, Vermont. U. S. Nat. Mus. Cat. No. 15336b. 
 lo. Transverse section of the two ^•alves in natural position, from Swanton, Vermont ( Locality 25a). The gaping 
 
 pedicle opening is well shown. L'. S. Nat. Mus. Cat. No. 15336c. 
 Ip. Enlargement of a cross section of a fragment of the shell from Locality 25a, Swanton, Vermont. V. S. 
 
 Nat. Mus. Cat. No. 15337e. 
 Iq. Enlargement of a longitudinal section of the shell at the apex of the ventral valve. Locality 25a, Lower 
 
 Cambrian, 2 miles east of Swanton, Vermont. I'. S. Nat. Mus. Cat. No. 15336d. 
 Ir and Is. Exterior of ventral and dorsal valves from Locality 392a, Lower Cambrian limestone at L'Anse 
 
 au Loup, Straits of BcUeisle, Labrador, Canada. V. S. Nat. Mus. Cat. Nos. 14893b and 14893c, 
 
 respectively. 
 
 KUTORGINA PECULIAKIS (Tate) (p. 583). 
 
 Figure 2. Top view of type specimen, a dorsal valve, from Locality 316a, Middle ? Cambrian, at Ardrossan, Yorke 
 Peninsula, South Australia. Original in the collection of the University of Adelaide, Adelaide, 
 South Australia. Cast in the United States National Museum (Cat. No. 58300). Specimen figiured 
 by Tate [1892, PI. II, fig. 5] as Orlhis (.?) peculiaris. 
 
 KUTORGINA PERUGATA Walcott (p. 583). 
 
 Figure 3. Exterior and side view of an exfoliated ventral valv<'. I'. S. Nat. Mus. Cat. No. 51511a. The outline of 
 the visceral area is dra^vn from another specimen. V. S. Nat. Mus. Cat. No. 51511g. 
 3a. Top and side views of a less elongate ventral valve than that represented by figure 3. V. S. Nat. Mus. 
 
 Cat. No. 51511b. 
 22 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH U PL. V 
 
 f'RANCeS W1ESER DEL 
 
 liQTV^E: CO BOSTON 
 
PLATE V. ■ 23 
 
 KuTORGiNA PERUGATA Walcott — Continued. 
 
 Figure 3b. Exterior, side, and back views of a dorsal valve. The pseudo-area is broken away. U. S. Nat. Mus. 
 
 Cat. No. 51511c. 
 3c. Top, back, and side views of an exfoliated dorsal valve, the type specimen, showing pseudo-area. U. S. 
 
 Nat. Mus. Cat. No. 51511d. 
 3d. Exterior of dorsal valve illustrating variation in the concentric corrugations. U. S. Nat. Mus. Cat. No. 
 
 51511e. 
 3e. Small, strongly corrugated ventral valve, drawn from the cast of a natural mold. U. S. Nat. Mus. Cat. 
 
 No. 51511f. 
 
 The specimens represented are all from Locality Iv, Lower Cambrian, Silver Peak quadrangle (U. S. Geol. Sur- 
 vey), Nevada. 
 
 KUTOEGINA SARDINIAENSIS Walcott (p. 584). 
 
 Figure 4. Ventral valve, the type specimen, from Locality 354e, Middle ? Cambrian, Sardinia. Copied from Borne- 
 
 mann [1891, PI. XIX, fig. 21], who de.s<-ribes and figures the specimen as Lingula roualli. 
 4a. Exterior of ventral valve from Locality 354e, Middle ? Cambrian shale at Porto Canal Grande, Sardinia. 
 
 U. S. Nat. Mus. Cat. No. 18301a. " 
 4b and 4c. Exteriors of dorsal valves from Locality 3S4e, Middle ? Cambrian, Sardinia. Copied from Borne- 
 
 mann [1891, PI. XIX, figs. 22 and 23, respectively], who describes and figures them as Kutorgina 
 
 cingtdata. 
 
 Kutorgina granulata Matthew (p. 582). 
 
 Figures 5 and 5a. Top and side views of a broken ventral valve. Type specimen figured l)y Matthew [1899a, 
 
 PL I, fig. 2a]; it is redrawn on this plate. 
 5b. Partly exf(jliated interior of a dor.sal valve. Specimen figured by Matthew [1899a, PL I, fig. 2c]; it is 
 
 redrawn on this plate. 
 5c. Partly exfoliated exterior of a dorsal valve. Specimen figured by Matthew [lS99a, PI. I, fig. 2b]; it is 
 
 redrawai on this plate. 
 
 The specimens represented are all from Locality 314b, Lower Cambrian limestone. Smith Sound, Newfoundland, 
 and are in the collection of the University of Toronto, Canada. 
 
PLATE VI. 
 
 25 
 
PLATE VI. 
 
 MiCKWiTZiA MONiLiFERA (Liiinarsson) (p. 330). 
 
 [PI. LIX, Ug. 2.] 
 
 Figures J, 1', and 1". Top, side, and back views of a partly exfoliated ventral valve. U. S. Nat. Miis. Cat. No. 
 
 51520a. 
 la. Top and side views of a small ventral valve. U. S. Nat. Mus, Cat. No. 51520b. 
 lb. Exfoliated dorsal valve. U. S. Nat. Mus. Cat. No. 51520c. 
 Ic. Interior of a dorsal valve. V. S. Nat. Mus. Cat. No. 51520d. 
 Id. Interior of a dorsal valve, showing a trace of the path of advance of the posterior lateral muscle scars. 
 
 U. S. Nat. Mus. Cat. No. 51520e. 
 le. Posterior view of a dorsal valve, showing the arching of the margin. The apex of the valve Ls broken away. 
 
 U. S. Nat. Mus. Cat. No. 51520f. 
 If. Interior of a worn dorsal valve, showing indications of a median depression and the path of advance of the 
 
 posterior lateral scars. U. S. Nat. Mus. Cat. No. 51520g. 
 Ig, Ih, li, and Ij. Ventral, dorsal, side, and back views of a cast of the two valves, the dorsal valve having 
 
 been crushed inward. U. S. Nat. Mus. Cat. No. 23893a. 
 Ik. Surface of an inner lamellation or layer of shell magnified six times. U. S. Nat. Mus. Cat. No. 51520h. 
 1 1. Surface of an inner layer of shell magnified about five times. This is a character illustrated by Linnarsson 
 
 [1896b, PI. XI, fig. 2]. U. S. Nat. Mus. Cat. No. 515201. 
 Im. Exterior layer of shell, partly worn so as to show sections of the papilla^ and punctte. The papillae 
 
 when unworn are elevated and have a minute opening at the apex (see fig. In). U. S. Nat. Mus. Cat. 
 
 No. 51520J. 
 In. Exterior papillose surface of a shell, greatly magnified. U. S. Nat. Mus. Cat. No. 51520k. 
 
 The specimens represented by figures 1, la-n are all from Locality 390j, Lower Cambrian Eophyton sandstone at 
 Lugnas, Province of Skaraborg, Sweden. 
 
 Figures lo and Ip. Side and back views of a cast of a compressed and somewhat distorted ventral valve from 
 Locality 396r, Lower Cambrian, at Streitberg, near Reval. Esthonia, Russia. Copied from Schmidt, 
 1888, PI. II, figures 12c and 12d, respectively. 
 
 MicKwiTZiA PRETiosA Walcott (p. 332). 
 
 Figure 2. Top view of the type specimen from Locality 390j, Lower Cambrian Eophyton sandstone at LugnSs. Province 
 of Skaraborg, Sweden. U. S. Nat. Mus. Cat. No. 51523a. Copied from Walcott [1908d, PI. VII, 
 fig. 2]. 
 
 MicKwiTZiA FORMOSA (Wimaii) (p. 329). 
 
 Figures 3, 3a, and 3b. Top, side, and posterior views of the type specimen from Locality 3H1, Middle? Cambrian, 
 sandstone on the peninsula of Biludden, Gofle Bay, Sweden. Original in the collection of the Univer- 
 sity of L^psala; cast in the L'nited States National Museum (Cat. No. 58299). 
 3c. Enlargement of a portion of the surface of one of the inner layers of the shell represented in figure 3, the 
 epidermal layer having iirobably been exfoliated. 
 
 The specimen represented was figured by "\\'iman [1902, PI. II, figs. 1-5] as Causea formosa . 
 
 MiCKMiTziA occiDENs Walcott (p. 331). 
 
 Figure 4. Type specimen, from Localily 174c, Lower Cambrian shale. Silver Peak quadrangle (U. S. Geol. Survey), 
 Nevada, showing outer and inner surfaces of the outer layer. IT. S. Nat. Mus. Cat. No. 51518a. 
 4'. Side outline of specimen represented by figure 4. 
 
 Figures 4 and 4' are copied from Walcott [190Sd, PL VII, fig.'*. 1 and 1']. 
 26 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. VI 
 
 PftANCES WIESER OEt 
 
 LiOTvPE CO Boston 
 
PLATE VII. 
 
 27 
 
PLATE VII. 
 
 Central lateral spat-e of area. 
 Outer lateral space of area. 
 Flexure line of area, 
 rmbonal muscle scar. 
 Central muscle scar. 
 Transmedian muscle scar. 
 Anterior lateral muscle scar. 
 
 k. Middle lateral muscle scar. 
 1. Outside lateral muscle scar, 
 p. Pedicle groove, 
 vs. Main vascular sinus. 
 X. Heart-shaped cavity. 
 x'. A slight depression of the bottom of the 
 heart-shaped cavity. 
 
 Obolus apollinis Eichwald (p. 381 J. 
 
 [Text figs. 4, p. 299, and 15. p. 299, and PI. XIV, figs. 0. 6a.] 
 
 Figures 1-6. Interiors of ventral valves illustrating variations in size, form, and position of the central, middle lateral, 
 and outside lateral muscle scars. From Locality 9d, Upper Cambrian Obolus sandstone, at Jaggowal, 
 east of Reval, Esthonia, Russia. U. S. Nat. Mus. Cat. No?. .!jl.524a-f, respectively. 
 
 7 and 8. Interiors of ventral valves from Locality 395b, Upper Cambrian Obolus sandstone, at Ilgast, Esthonia, 
 Russia, showing variation in form and arrangement of the muscle scars, central depression, etc. V. S. 
 Nat. Mus. Cat. Nos. 51525a and 51525b, respectively. 
 
 10, 11, and 12. Interiors of ventral valves from Locality 9d, Upper Cambrian Obolus sandstone, at Jaggowal, 
 Esthonia, Russia, showing variation in the form and arrangement of the muscle scars, central depres- 
 sion, etc. U. S. Nat. Mus. Cat. Nos. 35238a, 35238b, and 3523Sc, respectively. Specimens figured 
 by Walcott [1898b, PL XXVI, figs. 3-5, respectively]. 
 
 13. Fragment of the interior of a ventral valve from Locality 9d, Upper Cambrian Obolus sandstone, at Jaggo- 
 
 wal, Esthonia, Russia, in which the heart-shaped cavity is nearly lost, and in which the centrals, 
 middle laterals, and outside laterals are crowded into a narrow space. The drawing of the central 
 and outside lateral scars is somewhat conventionalized. U. S. Nat. Mus. Cat. No. 35238d. Specimen 
 figured by Walcott [1898b, PL XXVI, fig. 6]. 
 
 14, 15, 16, and 17. Interiors and posterior portions of dorsal valves from Locality 395b, L^pper Cambrian 
 
 Obolus sandstone, at Ilgast, Esthonia, Russia, showing the variation in position of muscle scars. 
 U. S. Nat. Mus. Cat. Nos. 51525c-f, respectively. 
 
 Obolus apollinis maximus ilickwitz (p. 384). 
 
 [PI. XIV. figs. 7 and 7a.] 
 
 Figure 9. Interior of a ventral valve in which the thickening of the shell is very great. 
 Cambrian Obolus sandstone, at Joa, near Jegelecht, Esthonia, Russia. 
 51528a. 
 28 
 
 From Locality 395, Upper 
 U. S. Nat. Mus. Cat. No. 
 
U S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. VII 
 
 FRANCES W1E9ER DEL. 
 
 ELiOTifPE CO BOSTON 
 
PLATE VIII. 
 
 29 
 
PLATE VIII. 
 
 a. Central lateral space of area. o'. Overlapping of lines of growth of area. 
 
 a'. Outer lateral space of area. p. Pedicle groove. 
 
 c. Trapezoidal area, including central, middle pvs. Peripheral branches of the vascular system. 
 
 lateral, and outside lateral muscle scars. ps. Parietal band.' 
 
 f. Flexure line of area. s. Median septum, 
 
 h. Central mtiscie scar. v. Visceral cavity, 
 
 i. Transmedian muscle scar. vs. Main vascular sinus, 
 
 j. Anterior lateral muscle scar. ivs. Lateral branches of vascular system. 
 
 k. Middle lateral muscle scar. x. Heart-shaped cavity. 
 1. Outside lateral muscle scar. 
 
 Obolus matixalis (Hull) (p. 400). 
 
 Figure 1. E.icterior of an almost perfect ventral valve from Locality 328e, a Middle Cambrian horizon in the "St. Croix 
 sandstone," St. Croix Falls, Wisconsin. U. S. Nat. Mus. Cat. No. 51.564a. 
 
 la. Large, partly exfoliated ventral valve from Locality 67c, Upper C'ambrian sandstone, Tatur Hill, Burnet 
 County, Texas, showing the radial striation of the inner layers of the .shell. U. S. Nat. Mus. Cat. No. 
 52420a. 
 
 lb. Partly exfoliated ventral valve from Locality 67, L'pper Cambrian sand.stone, Tatur Hill, Burnet County, 
 Texas. U. S. Nat. Mus. Cat. No. 52419a. 
 
 Ic. Partly exfoliated ventral valve associated with the specimen represented by figure 1. U. S. Nat. Mus. 
 Cat. No. 51.564b. 
 
 Id. Cast of the interior of a ventral valve showing the details of the interior of the shell with unusual clear- 
 ness, from Locality 82b, Upper Cambrian "St. Croix sandstone," Taylors Falls, Chisago County, 
 Minnesota. U. S. Nat. Mus. Cat. No. 51563a. 
 
 le. Cast of the interior of a ventral valve associated with the valve represented by figure 1. U. S. Nat. Mus. 
 Cat. No. 51564c. 
 
 If. Interior of a broken ventral valve from Locality 339d, Upper Cambrian "St. Croix sandstone" at Taylors 
 Falls, Minnesota, showing the thickened shell under the visceral area. U. S. Nat. Mus. Cat. No. 
 51563c. 
 
 Ig. Interior of a ventral valve, in which there is no special thickening beneath the visceral area, associated 
 with the specimen represented by figure If. U. S. Nat. Mus. Cat. No. 51563d. 
 
 Ih. Cast of the interior of a dorsal valve associated with the specimen represented by figure Id. U. S. Nat. 
 Mus. Cat. No. 51563b. 
 
 li. Cast of the interior of a dorsal valve associated with the valve represented by figures 1, Ic, and le. L". S. 
 Nat. Mus. Cat. No. 51564d. 
 
 Ij. Interior of a ventral valve in which there has been a considerable thickening of the shell .«o as to form a 
 platform to which the muscles and visceral parts were attached. From Localit\ 339d, I'pper Cam- 
 brian "St. Croix sandstone." Taylors Falls, Minnesota. \J. S. Nat. Mus. Cat. No. 51.563c. 
 
 Ik. Partly exfoliated dorsal valve from Locality 71, I'pper Cambripn limestone. Cold Creek Canyon, Burnet 
 County, Texas. U. S. Nat. Mus. Cat. No. 51566a. 
 
 Obolus tetonensis ninus Walcott (p. 4LS). 
 
 [PI. XI, figs. 1, la-g.] 
 
 Figure 1 1. Ventral vSlve, showing the strongly marked radiating stria; of the inner layers, 
 lin. Cast of the interior of a ventral valve. 
 In. Cast of the interior of a dor.sal valve, 
 lo. Cast of the interior of a partly exfoliated dorsal valve. 
 
 The specimens represented by figures 1 1 to lo are from Locality 68, Upper Cambrian saiidstone, Packsaddlc Moun- 
 ' tain, Llano County, Texas. U. S. Nat. Mus. Cat. Nos. 51644a-d, respectively. 
 
 Obolus namouna Walcott (p. 406). 
 
 Figure 2. Cast of the interior of a ventral valve, the type specimen, associated on the same hand spe<-imen with 
 the shells of Obolus rliai represented by figiu-es la and lb, Plate IX, from Locality 98, Upper Cambrian 
 "St. Croix sandstone," Eau Claire, Wisconsin. U. S. Nat. Mus. Cat. No. 27304a. 
 30 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. VIII 
 
 FRANCES WIESER DEL. 
 
 LlOT/PC CO 90SI0N 
 
PLATE VIII. 31 
 
 Obolus NAMOtJNA Walcott— Continued. 
 
 Figure 2a. Cast of the interior of a dorsal valve associated on the same hand specimen with the specimen represented 
 by fagure 2. The remarkable feature of this specimen is the continuation of the lines of growth of the 
 area far forward on the shell. U. S. Nat. Mus. Cat. No. 27304b. 
 
 Obolus matinalis (Hall) ? WaU-ott (p. 402). 
 
 Figures 3 and 3a. Ventral and dorsal valves of partly e.xfoliated shells from Locality C54, Upper Cambrian Chau- 
 mitien limestone two-thirds mile west of Tsinan, Shantung, China. U. S. Nat. Mus. Cat. Nos 
 52o33a and o2r)33b, respectively. 
 
PLATE IX. 
 
 62667°— VOL 51, pt 2—12 ^3 33 
 
PLATE IX. 
 
 Central lateral space of area. 
 
 Outer lateral sjiace of area. 
 
 Trapezoidal area, includinf; central, middle 
 
 lateral, and outside lateral muscle scars. 
 Flexure line of area. 
 Central muscle scar. 
 
 j. .\nterior lateral muscle scar. 
 
 p. Pedicle groove, 
 ps. Parietal band. 
 
 V. Visceral cavity, 
 vs. Main vascular sinus. 
 
 X. Heart-shaped cavity. 
 
 Oboli^s RHEA Walcott (p. 410). 
 
 Figure 1. Cast of the interior of a ventral valve, the type specimen, from Locality 98, T'])per Cambrian "St. Croix 
 sandstone," Eaii Claire, Wisconsin, which shows the median, pestlo-shaped ridge that filled the 
 corresponding groove on the interior of the shell, (.'asts of the lines of growth and the visceral area 
 are also finely preserved. U. S. Nat. Mus. Cat. No. 27300a. 
 
 la. Cast of the interior of a ventral valve from Locality 98, Upper Cambrian "St. Croix sandstone," Eau 
 Claire, Wisconsin, in which some of the details of the anterior part of the visceral cavity are more 
 clearly defined than in the specimen represented by figure 1. XJ. S. Nat. Mus. Cat. No. 27300b. 
 
 lb. A dorsal valve, associated on the same hand specimen with the specimen represented by figure la, from 
 which the shell has been almost wholly exfoliated. U. S. Nat. Mus. Cat. No. 27300c. 
 
 The specimens represented in figures la and lb are on the same slab of sandstone as the two specimens of Obolus 
 namouna represented by figures 2 and 2a, Plate VIII. 
 
 Figure Ic. Cast of the interior of a dorsal valve from Locality 84, a Middle Cambrian horizon in the "St. Croix sand- 
 stone," Dresbach, Minnesota, showing the area and traces of the vascular markings. U. S. Nat. 
 ■ Mus. Cat. No. 52430a. 
 
 Obolus eefulgens Matthew (p. 409). 
 
 Figure 2. Cast of the interior of a ventral valve, the type specimen, that is flattened in the shale. University of 
 Toronto, Canada. Redrawn from the specimen figured by Matthew [1892, PI. XII, fig. 6d (ventral)] 
 as Obolus rrfiiUjens: and copied by him [1903, PI. XI, fig. 4a] as MonoboUna rcfidgens. 
 
 2a. Cast of the interitjr of a dorsal valve that preser\-cs the original convexity. L^niversitj' of Toronto, Canada. 
 Redrawn from the specimen figured by Matthew [1892, PI. XII, fig. 6d (dorsal)] as Obolus refidgens; 
 and copied by him [1903, PI. XI, fig. 4b] as MonoboUna refidgens. 
 
 2b. Ventral valve flattened in the shale and compressed laterally so as to give it more the outline of Lingulella 
 than of Obolus. L^niversity of Toronto, Canada. 
 
 2c and 2d. Dorsal valves flattened in the shale and slightly distorted. L'nivcrsity of Toronto, Canada. 
 
 The specimens represented all occur in Locality 308, LTpper Cambrian, Division 3c of Matthew, Navy Island, 
 St. John Harbor, New Brunswick. Specimens represented by figures 2 and 2a occur in an arenaceous shale which 
 preserves the specimens in better condition than in the argillaceous shales. 
 
 Oboli's pandemia Walcott (p. 407). 
 
 P^GURE 3. Exterior of a slightly flattened and distorted ventral valve. U. S. Nat. Mus. Cat. No. 27301a. 
 
 3a. Cast of the interior of a ventral valve, the type specimen, that has been compressed in its posterior portion 
 
 so as to force the visceral ca\'ity back nearly to the area. U. S. Nat. Mus. Cat. No. 27301b. 
 3b. Interior of the ventral valve showing an elevated pestle-shaped median ridge that occupies the place of 
 
 the heart-shaped cavity of most species of Obolus. V. S. Nat. Mus. Cat. No. 27301c. 
 3c. Cast of the interior of a dorsal valve, showing the area. U. S. Nat. Mus. Cat. No. 27301d. 
 3d. Cast showing part of (he interior of a dorsal valve, showing traces of the central muscle sqars, and the 
 
 thick lamination of the .shell toward the margin. U. S. Nat. Mus. Cat. No. 27301e. 
 
 The specimens represented are all from Locality 10a, Middle Cambrian, Bays Mountains, Knoxville, Tennessee. 
 
 Obolus lopeki Walcott (p. 395). 
 
 FiGUKE 4. Imperfect ventral valve from Locality 335a, Cambro-Ordovician sandstone, Cement Creek, 3 miles north 
 of Hot Springs, Ouray County, Colorado, showing the general form and the several layers forming 
 the shell. U. S. Nat. Mus. Cat. No. 27303a. 
 4a. Partly exfoliated dorsal valve, the type specimen, associated with the specimen represented ly figure 4. 
 V. S. Nat. Mus. Cat. No. 27303b. 
 34 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH L' iL. I/, 
 
PLATE IX. 35 
 
 Obolus tetonensis Walcott (p. 417). 
 
 Figure 5. A ventral valve, the type specimen, with the anterior portion of the shell exfoliated, from Locality 4e, 
 
 Middle Cambrian limestone, Teton Mountains, Wyoming. U. S. Nat. Mus. Cat. No. 51639a. 
 5a. Dorsal valve associated with specimen represented by figure 5. U. S. Nat. Mus. Cat. No. 51G39b. 
 5b. Outline of the two valves, showing their convexity. Drawn from specimen associated with specimens 
 
 represented by figures 5 and 5a. U. S. Nat. Mus. Cat. No. 51639c. 
 5c. A small ventral \alve from Locality 4m, Middle Cambrian sandstone in the Teton Mountains, Wyoming. 
 
 r. S. Nat. Mus. Cat. No. 35220a. 
 5d. Dorsal valve associated with specimen represented by figure 5c. This shell may belong to some other 
 
 species. U. S. Nat. Mus. Cat. No. 35220b. 
 
 Obolus woetheni Walcott (p. 421). 
 
 [Te.xt flgs. 39A-D, p. 421.] 
 
 Figure 5e. A very finely preserved interior of a small dorsal valve, the type specimen, from Locality 54u, Middle 
 Cambrian limestone, 2 miles southeast of Malade, Idaho. U. S. Nat. Mus. Cat. No. 51638a. Copied 
 from Walcott [1908d, PI. VII, fig. 17]. 
 
PLATE X. 
 
 37 
 
PLATE X. 
 
 c. Trapezoidal area, including central, middle s. Median septum. 
 
 lateral, and outside lateral muscle scars. v. V'isceral cavity, 
 
 h. Central muscle scar. vs. Main vascular sinus. 
 j. Anterior lateral muscle scar. x. Ilcart-shaped cavity. 
 
 Obolus mickwitzi Walcott (p. 403). 
 
 Figure 1. Cast of a small veutral valve, the type specimen, showing tho dfejily impressed vascular and vi.sceral mark- 
 ings. It will be noted that the visceral cavity extends far forward. U. S. Nat. Mas. Cat. No. 27299a. 
 
 la. Cast of the interior of a ventral valve in which the visceral cavity is much larger proportionally than that 
 represented in figure 1, and in which the areas occupied by the central, middle lateral, and outside 
 lateral scars are unusually large and i)rominent. More than two-thirds of the entire length of the 
 shell is taken up by the visceral area. U. S. Nat. Mus. Cat. No. 27299b. 
 
 lb. Portion of the cast of a small ventral valve in which the interior markings have been still more deejdy 
 impressed than in the specimens shown by figures 1 and la. The heart-shaped cavity (x), the trape- 
 zoidal area (c), and the main vascular sinus (vs) must have been placed upon a strongly built up 
 platform in the interior of the shell. U. S. Nat. Mus. Cat. No. 27299c. 
 
 Ic. Cast of the interior of a large ventral valve in which the visceral area is limited to the ])osterior half of the 
 shell. U. S. Nat. Mus. Cat. No. 27299d. 
 
 Id. Cast of the interior of a large dorsal valve which shows the relative position of the central (h) and anterior 
 lateral (j) muscle scars, and the form of the visceral cavity. U. S. Nat. Mus. Cat. No. 27299e. 
 
 le. Partly exfoliated dorsal valve which illustrates the lamcllated character of the shell and the strong 
 concentric undulations of growth which appear on some specimens. V. S. Nat. Mu.'i. Cat. No. 
 27299f. 
 
 If. Cast of a large dorsal valve in which the visceral area is mainly upon the posterior half, as in the ventral 
 valve represented by figure Ic. l\ S. Nat. Mus. Cat. No. 27299g. 
 
 Ig. Cast of the interior of a small dorsal valve in which the visceral area occupies the central iiortion of the 
 shell. U. S. Nat. Mus. Cat. No. 27299h. 
 
 Ih. Cast of the interior of a dorsal valve showing a remarkable development of the area about the central 
 muscle scars. U. S. Nat. Mus. Cat. No. 272991. 
 
 li. Cast of the interior of a ventral valve in which the main vascular sinus and other inlerior markings of 
 the shell are less deeply impressed than in specimens represented by figures la and 11>, 
 
 The specimens represented in figures 1, la-i are from Locality 79, Upper Cambrian sandstone, at Hudson, Wis- 
 consin. 
 
 Figure Ij. Cast of a ventral valve which is somewhat doubtfully referred to this species, owing to its not showing the 
 same strong interior markings. This, however, may be the result 'of the condition of ]ir('servation. 
 U. S. Nat. Mus. Cat. No. 56937a. 
 Ik. Partly exfoliated dorsal valve associated with the specimen represented by figure Ij. It is probable 
 that a larger collection of material would show that figures Ij and Ik represent a distinct species. 
 IT. S. Nat. Mus. Cat. No. 56937b. 
 
 The specimens represented in figures Ij and Ik are from Locality 79b, UpiJcr Cambrian .sandstone at Hudson, 
 Wisconsin, a slightly diSerent horizon than the one containing the specimens represented in figures 1, la-i. 
 
 Obolus u^ra (Hall and Wliitfield) (p. 399). 
 
 FiouKE 2. Partly exfoliated and broken ventral valve from Locality 313j, Upper Cambrian limestone. Eureka 
 
 district, Nevada. U. S. Nat. Mus. Cat. No. 24552a. 
 2a. Partly exfoliated dorsal valve associated with the specimen represented by figure 2. U. S. Nat. Mus. 
 
 Cat. No. 24552b. Type specimen figured by Hall and WTiitfiekl [1877, PI. I, fig. 6] as Lingulepis msera. 
 2b. More elongated, partly exfoliated dorsal valve from Locality 313j, Upper Cambrian limestone, Eureka 
 
 district, Nevada. U. S. Nat. Mus. Cat. No. 24552c. Specimen figured by Hall and Whitfield 
 
 [1877, PI. I, fig. 5] as Lingulepis inxra. 
 2c. Crushed and partly exfoliated ventral valve, doubtfully referred to this species, from Locality 205, 
 
 limestone forming passage beds between the Upper Cambrian and the Ordovician, on Roundtop 
 
 Mountain, Eureka district, Nevada. U. S. Nat. Mus. Cat. No. 51562a. 
 38 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. X 
 
 FRANCES WIESER DEL. 
 
PLATE X. 39 
 
 Obolus m^ra (Hall juul Wliitlield) — Continued. 
 
 Figure 2d. Exfoliated ventral valve from Locality 61, I'pper Cambrian Dunderberg shale, south of the Hainburg 
 
 mine, Eureka district, Nevada, showing outline of visceral area. U. S. Nat. Mus. Cat. No. 515Gla. 
 
 2e. Partly exfoliated ventral valve, showing radial striation of interior layers of the shell. Locality 88, 
 
 Middle Cambrian Secret Canyon shale, New York and Secret canyons, Eureka district, Nevada. 
 
 U. S. Nat. Mus. Cat. No. olofiOa. 
 
 Oboi.vs anceps Walcott (p. 380). 
 
 Figure 3. Partly exfoliated ventral valve. U. S. Nat. Mus. Cal. No. 27302a. 
 
 3a. Partly exfoliated ventral valve showing the area. L'. S. Nat. Mus. Cat. No. 27302b. 
 
 3b. Cast of the interior of a dorsal valve, the type specimen, showing the area and traces of the vascular 
 
 markings. I". S. Nat. Mus. Cat. No. 27302c. 
 3c. More elongated dorsal val\-e than that represented by figure 3b. U. S. Nal. Mu.s. Cat. No. 27302d. 
 
 The specimens represented in figures 3, 3a-c are all from Locality 63. Lower Ordovician Pogonip limestone, north- 
 east of Adams Hill, Eureka district, Nevada. 
 
 Figure 3d. Ventral valve. U. S. Nat. Mus. Cat. No. .51541a. 
 
 3e. Partly exfoliated dorsal valve showing interior layers of the shell. U. S. Nat. Mus. Cat. No. 51541b. 
 3f. Exterior of dorsal valve. U. S. Nat. Mus. Cat. No. 51541c. 
 
 The specimens represented in figures 3d-f are from Locality 61, Upper Cambrian Dunderberg shale, south of the 
 Hamburg mine, Eureka district, Nevada. 
 
 Obolus .sp. uiidt. a Walcott (p. 422). 
 
 Figure 4. Ventral valve compressed in shaly limestone of Locality 338v, I^ower Ordovician, 1 mile southwest of 
 Middle Granville, Washington County. New York. U. S. Nat. Mus. Cat, No. 51G52a 
 
PLATE XI. 
 
 41 
 
PLATE XI. 
 
 a. Area. h. Central muscle scar, 
 
 c. Trapezoidal area, including central, middle j. Anterior lateral muscle scar, 
 
 lateral, and outside lateral muscle scars. 
 
 Obolus tetonensis ninus Walcott (p. 418). 
 
 [PI. VIII, figs. 11-0. J 
 
 Figures 1 and 1'. Top and side views of exterior of ventral valve, the type specimen. V. S. Xal. Mils'. Cat. 
 
 No. 51(i4;!a. 
 la. Partly exfoliated ventral valve. V. S. Nat. Mus. Cat. No. 51643b. 
 
 lb. Interior of ventral valve, show-ing outline of visceral area. U. S. Nat. Mils. Cat. No. 51643c. 
 Ic. Dorsal vah'e, showing lamellation of shell. U. S. Nat. Mus. Cat. No. 51643d. 
 Id and Id'. Exfoliated dorsal valve, showing striation (jf interior layers of shell. 1'. K. Nat. Mus. Cat. No. 
 
 51643e. 
 le and If. Exfoliated dorsal valves, showing character of interior layers of shell and variation in form from 
 
 specimens represented by figures Ic and Id. U. S. Nat. Mus. Cat. Nos. 51643f and 51643g, respectively. 
 Ig. Cast of broken dorsal valve, showing anterior position of visceral area, and the central and anterior lateral 
 
 scars. U . S. Nat. Mus. Cat. No. 51643h. 
 
 The specimens represented are all from Locality 9r, Upper Cambrian limestone in the Reagan sandstone, Coman- 
 che County, Oklahoma. 
 
 Obolus (Westonia) themis Walcott (p. 466). 
 
 Figure 2. Exterior of ventral valve, the type specimen, showing broken edges of lamellae of the shell. U. S. Nat. 
 
 Mus. Cat. No. 51732a. 
 2a. Dor-sal valve, showing the .same shell characters as figure 2. U. S. Nat. Mus. Cat. No. 51732b. 
 2b. Broken ventral valve, showing cast of the visceral cavity and main vascular trunks. U. S. Nat. Mus. 
 
 Cat. No. 51732c. 
 2c. Partly exfoliated dorsal valve, posterior margin broken away. I'. S. Nat. Mus. Cat. No. 51732d. 
 
 The specimens represented are all from Locality 17c, Middle Cambrian sandy limestone on Grand \'iew trail, 
 south side Grand Canyon of the Colorado, Arizona. 
 
 Obolus ismene Walcott (p. 393). 
 
 Figure 3. Portion of .-entral valve, the type specimen, showing cardinal slopes and the striation of one ^^f the inner 
 layers of shell. U. S. Nat. Mus. Cat. No. 51545a. 
 3a. Partly exfoliated dorsal valve. V . S. Nat. Mus. Cat. No. 51545b. 
 3b. Interior of a dorsal valve showing area. L". S. Nat. Mus. Cat. No. 51545c. 
 
 The specimens represented are all from Locality 369, Upper Cambrian sandstone in the Elvins formation, Flat 
 River, St. Francois County, Missouri. 
 
 Obolus nundina Walcott (p. 406). 
 
 Figure 4. Ventral valve, the type specimen, showing the characteristic strong concentric ridges. 
 4a. Partly exfoliated dorsal valve. 
 
 The specimens represented are on the same piece of limestone from Locality 14b. Upper Cambrian, Cold Creek, 
 Llano County, Texas. U. S. Nat. Mus. Cat. Nos. 51587a and 51.587b, respectively. 
 
 Obolus acadicus Walcott (p. 380). 
 
 Figure 5. Cast of the interior of a dorsal valve, the type specimen, from Locality 3h. I'pper Cambrian shale, McNeil 
 Brook, Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. No. 51540a. The i)i)sterior portion of the 
 shell was restored from another specimen (Catalogue No. 5I.540b), the two being counterparts. 
 
 Obollts pheres Walcott (p. 408). 
 
 Figures 6 and fia. Views of partly exfoliated ventral valves, showing thickness of the lamellated .^hell. U. S. Nat. 
 Mus. Cat . No. 51.589a and 51.589b, respectively. Figure 6 represents the type specimen. 
 Gb. Imperfect dorsal valve. U. S. Nat. Mus. Cat. No. 51589c. 
 
 The specimens represented are all from Locality lOv, U|>per Candirian shale near Baraboo, Wi.-sconsin. 
 
 42 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. X! 
 
 FRANCES WItSEB DEL, 
 
 HELiorvpE CO ao5TON, 
 
PLATE XI. 43 
 
 Obolus shansiensis Walcott (p. 415). 
 
 Figure 7. Broad form of the ventral valve from Locality C32, Middle Cambrian river drift on the Nankiang, 1 mile 
 
 south of Chonpinghien, Shensi, China. U. S. Nat. Mus. Cat. No. 52537a. 
 7a. Narrow form of the ventral valve, the type specimen, from Locality C37, Middle Cambrian Kichou 
 
 limestone, 8 miles south of Tinghianghien, Shansi, China. U. S. Nat. Mus. Cat. No. 52538a. 
 7b. Broad form of the dorsal valve associated with the ventral valve represented by figure 7. U. S. Nat. Mus. 
 
 Cat. No. 52537b. 
 7c. Narrow form of the dorsal valve associated with the ventral \-alve represented by figure 7a. V. S. Nat. 
 
 Mus. Cat. No. 52538b. 
 
 Obolus minimus Walcott (p. 404). 
 
 Figure 8. A partly exfoliated ventral valve, the type specimen, showing the cast of the visceral area and the main 
 vascular canals. 
 8a. Exterior of dorsal valve. 
 
 The specimens represented are both from Locality CI, Middle Cambrian Kiuluiig limestone, 2 miles south of Yen- 
 chuang, Sintai district, Shantung, China. U. S. Nat. Mus. Cat. Nos. 52534a aud 52534b, respectively. 
 
 Obolus obscurus Walcott (p. 406). 
 
 Figure -Q. Interior of an imperfectly preserved dorsal valve, the type specimen. U. S. Nat. Mus. Cat. No. 52536a. 
 9a. Exterior of an exfoliated, partly restored dorsal valve. U. S. Nat. Miis. Cat. No. 52536b. 
 
 The specimens represented in figures 9 and 9a are both from Locality C63, Middle Cambrian sandy shale at the 
 base of the Kiulung group, 3.5 miles southwest of Yenchuang, Sintai district, Shanlung, China. 
 
 Figure 9b. Partly exfoliated and broken ventral valve, showang concentric and radiating lines on the inner layers 
 of the shell. U. S. Nat. Mus. Cat. No. 52535a. 
 9c. Enlargement of the concentric striae of the exterior surface. U. S. Nat. Mus. Cat. No. 52535b. 
 9d. Exterior surface of a broken dorsal valve. U. S. Nat. Mus. Cat. No. 52535c. 
 
 The specimens represented in figures 9b-d are from Locality C75, Middle Cambrian limestone near the base of the 
 Kichou formation, 4.5 miles south of Wutaihien, Shansi, China. 
 
PLATE XII. 
 
 45 
 
PLATE XII. 
 
 a. Trapezoidiil area, iiicluditifj centra!, middle j. Anterior lateral muscle scar. 
 
 lateral, and outside lateral muscle scars. p. Pedicle groove, 
 
 h. Central muscle scar. vs. Main vascular sinus, 
 
 i. Transmedian nuisde scar. jvs. Lateral branches of the vascular system. 
 
 Obolus feistmanteli (Barrandp) (p. 391). 
 
 [PI. XII, figs. 9 and 93.) 
 
 Fir.uKE 1. Interior of ventral valve. Copied from Barrande [1879b, PI. CVI, fii^. iv: 7A]. 
 
 la. Cast of exterior surface of ventral valve, showing traces of concentric strise and lines of growth. Copied 
 from Barrande [1879b, PI. CVI, fig. iv: llA]. 
 
 lb. Cast of interior of ventral valve. Original in the collection of the Museum of Comparative Zoology, Cam- 
 bridge, Massachusetts; cast in the United States National Museum (Cat. No. 57088a). 
 
 Ic. Cast of interior of ventral valve, showing lateral vascular canals. Original in the Museum of Com- 
 parative Zoology; cast in the United States National Museum (Cat. No. .57088b). 
 
 Id. Interior of the type specimen, a ventral valve. Copied from Barrande [lS79b, PI. CVI, fig. iv: 4 A]. 
 
 le. Cast of the interior of a dorsal valve, showing traces of lateral va.scular canals. Original in the Museum of 
 Comparative Zoology; cast in the United States National Museum (Cat. No. .570S8c). (See fig. 9a.) 
 
 If. Enlargement of a portion of a partly exfoliated shell, showing structure of shell. Copied from Barrande 
 [1879b, PI. CVI, fig. IV : 12f]. 
 
 The specimens represented are all from Locality 3031, Lower Ordovician sandstone, Etage dl, Kruschna nora, 
 Bohemia. 
 
 Obolits ? ANCiLLUS (BaiTaiide) (p. 381). 
 
 Figure 2. Partly exfoliated ventral valve, the type specimen, from Locality 303g, Lower Ordovician, Etage dl, 
 Rabenberg, Bohemia. Copied from Barrande [1879b, -PI. CXI, fig. vi: 3A]. 
 
 Obolus complexus Barramle (p. 387). 
 
 |P1. XII, figs. Sand 8a.] 
 
 FiGVRE 3. Cast of interior of ventral valve, the type specimen, from Locality 3031, Lower Ordovician, Etage dl, 
 Kruschna Hora, Bohemia. Copied from Barrande [1879b, PI. CLII, fig. ii: 4A]. 
 3a. Interior of dorsal valve from Locality 3031, Lower Ordovician, Etage dl, Kruschna Hora, Bohemia. Copied 
 from Barrande [lS79b, PI. CXIII, fi-. v: A]. 
 
 Obolus? mirandus (Barrande) (p. 405). 
 
 Figure 4. Ventral valve, the type specimen, from Locality 303k, Lower Ordovician, Etage dl, Hradischt, Bohemia. 
 Copied from Barrande [1879b, PI. CXI, fig. i: 3A]. 
 4a. Dorsal? valve from Locality 303k, Lower Ordo\-ician, Etage dl, Hradischt, Bohemia. Copied from 
 Barrande [1879b, PI. CXI, fig. i: lA]. 
 
 Obolus? advenus Barrande (p. 380). 
 
 Figure 5. Cast of interior of ventral valve, the type specimen, from Locality 303d, Lower Ordovician, Etage dl, 
 Swarow, Bohemia. Copied from Barrande [1879b, PI. XCV, fig. iv: 2A]. 
 oa and .'ilj. Exterior and side ^'iew of dorsal? valve from Locality 303d, Lower Ordovician, Etage dl, Swarow, 
 liohemia. Co))iod from Barrande [lS7llb, PI. XCV, figs, iv: lA and 2B, respectively]. 
 
 Odolus? rokitzanensis Barnuide (p. 411). 
 
 FiGURK G. Cast of the interior of a ventral valve, the t>-pe specimen, from Locality 303b, Lower Ordovician, Etago 
 dl, in the envdrons of Rokitzan, Bohemia, showing strong radiating stria?. Copied from Barrande 
 [1879b, PI. CXXVI, fig. ii: hA]. 
 46 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XII 
 
 FRANCES WIESefi DEL. 
 
 KELIOTYPC CO SOSl 
 
PLATE XII. 47 
 
 Obolus? (Westonia?) lamellosus (Barrande) (p. 463). 
 
 FiouEE 7. Enlargement of a dorsal valve, the type specimen. Copied from Barrande [1879b, PI. CVI, fig. i: 2A]. 
 7a. Surface and lamella; of shell greatly enlarged. Copied from Barrande [1879b, PI. CVI, fig. i: 3f]. 
 7b. Elongate dorsal valve. Copied from Barrande [1879b, PI. CXI, fig. ix: 2A]. 
 7c. Distorted ventral ? valve. Copied from Barrande [1879b, PI. CXI, fig. i.x: lA]. 
 
 7d. Enlargement of the surface of the specimen represented in figure 7c. Co]iie<l from Barrande [lS79b, PI. 
 CXI, fig. ix: If]. 
 
 The specimens represented are all from Locality 303 1, Lower Ordo\ician, Etage dl, Libetschov, B(^llemia. 
 
 Obolus complexus Barrande (p. 3S7). 
 
 fPl. XII. figs. 3 and 3a.] 
 
 Figures 8 and 8'. Cast of interior and side outline of a ventral ? valve from Locality 303i, Lower Ordovician, Etage 
 dl, Kruschna Hora, Bohemia. Copied from Barrande [lS79b, PI. XCV, figs, in: W and IB, respec- 
 tively]. 
 8a. Supposed cast of interior of dorsal valve from Locality 303h, Lower Ordovician, Etage dl, Milinsky Wrch, 
 near Woleschna, Bohemia. Copied from Barrande [1879b, PI. XCV, fig. in: 2C]. 
 
 Obolus feistmanteli (Barrande) (]x .391). 
 
 IPl.XII, figs. 1, la-f.I 
 
 9. Cast of the inner surface of the frontal rim of the shell, greatly enlarged. Original in the Museum of Com- 
 parative Zoology; cast in the Ignited States National Jluseuuf (Cat. No. .'57088d). 
 
 9a. Traces of the minute terminal vessels that cross the inner surface near the anterolateral margins of the 
 shell; greatly enlarged from a portion of the surface of the specimen represented by figure le. Original 
 in the Museum of Comparative Zoology; cast in the United States National Museum (Cat. No. 57088c). 
 
 The specimens represented are both from Locality 3031, Lower Ordovician sandstone, Etage dl, Kruschna Hora, 
 Bohemia. 
 
PLATE XIII. 
 
 62667°— VOL 51, PT 2—12 1 49 
 
PLATE XIII. 
 
 Obolus (Broggeria) salteki (Iloll) (p. 424). 
 
 [PI. XV, figs. 4, 4a-d.) 
 
 Figure 1. Exterior of ventral valve from Locality 309i, Upper Cambrian near Sandby, Province of Malmohus, Sweden. 
 
 U. S. Nat. Mus. Cat. No. 51673a. 
 la. Ventral valve associated with the specimen represented by figure 1, showing a cast of part of the interior 
 
 of the shell. U. S. Nat. Mus. Cat. No. 51673b. 
 lb. Cast of the interior of a dorsal valve associated with the specimen represented by figure ]. U. S. Xat. 
 
 Mus. Cat. No. 51673c. 
 Ic. Cast of the interior of a ventral valve from Locality 3091, Upper Cambrian, Sweden (exact locality 
 
 unknown), showing the area, more or less of the maui vascular .■^inuse.':, and the visceral cavity. U. S. 
 
 Nat. Mus. Cat. No. 5139Sa. 
 Id. Cast of the interior of a ventral valve from Locality 101, Upper Cambrian shales, east bank of BarachoLs 
 
 River, G miles from Little Bras d'Or Lake, Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. No. 
 
 51671a. 
 
 10. Cast of the interior of a ventral valve from Locality 3q, L'pper Cambrian shale.?, Barachois Glen, 4 miles 
 
 south of Little Bras d'Or Lake, Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. No. 52441a. 
 
 If. Cast of the interior of a dorsal valve from Locality 309 1, L'pper Cambrian, Sweden (exact locality unknown). 
 U. S. Nat. Mus. Cat. No. 5139Sb. 
 
 Ig. Cast of exterior of a ventral valve from Locality lOi, Upper Cambrian shales, Barachois River, north of 
 Boisdale road. Cape Breton, Nova Scotia, with a portion of the shell covering the area broken away. 
 U. S. Nat. Mus. Cat. No. 52442a. 
 
 Ih, li, and Ij. Casts of dorsal valves from Locality 101, Upper Cambrian shales, cast bank of Barachois River, 
 6 miles from Little Bras d'Or Lake, Cape Breton, Nova Scotia, varying in outline, owing to compres- 
 sion in the shale. U. S. Nat. Mus. Cat. Nos. 51671b, 51671c, and 51671d, respectively. 
 
 Ik. Cast of dorsal valve from Locality' Sq, ITpper Cambrian shales, Barachois Glen, 4 miles south of Little 
 Bras d'Or Lake, Cape Breton, Nova Scotia. L'. S. Nat. Mus. Cat. No. 52441b. 
 
 11. Cast of dorsal valve from Locality 101 Upper Cambrian shales, Barachois River, north of Boisdale road, 
 
 Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. No. 52442b. 
 
 Im. Cast of the interior of a dorsal valve from Locality 323f, Ceratopyge limestone at \'estfossen, 10 miles 
 west-southwest of Christiania, Norway, reproduced from a photograph. The markings of the vas- 
 cular system are beautifully preserved in the cast. L^niv. Min. Inst. Christiania, Norway. Specimen 
 illustrated by Brogger [1S82, PI. X, fig. 10] as Obolus salteri. 
 
 In. Interior of a ventral valve from Locality 323w, Upper Cambrian at Christiania, Norway, flattened in shale. 
 It is one of the largest shells of this specie ; known to the author. Univ. Min. Inst. Christiania, Norway. 
 
 Obolus (Acritis rvgatu.s Walcott (p. 441). 
 
 Figure 2. Exterior view of the type specimen from Locality 58, Middle Cambrian Secret Canyon shale. New York 
 and Secret canyons, Eureka district, Nevada. U. S. Nat. Mus. Cat. No. 35229a. 
 
 Obolus (Acritis) axtiquissimus (Eichwald) (p. 437). 
 
 [I'l. XV, figs. 2, 2a-d.] 
 
 Figure 3. Surface of shell enlarged four and one-half times. Locality 396d, passage bed.s between the Upper Cambrian 
 and the Ordovician, "glauconite limestone," at Domglint, in Reval, Esthonia, Russia. I'. S. Nat. 
 Mus. Cat. No. 51534a. 
 50 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. Xlll 
 
 FRANCES WlESEFt DEL. 
 
 MELIOTyPE CO BOSTON 
 
PLATE XIV. 
 
 51 
 
PLATE XIV. 
 
 c. Trapezoidal area, Including central, middle 
 lateral, and outside lateral muscle scars, 
 h. Central muscle scar. 
 i. Transmedian muscle scar, 
 j. Anterior lateral muscle .soar. 
 
 I. Outside latt-ral muscle scar. 
 vs. Main vascular sinus, 
 s. Median septum. 
 .X. Heart-shaped cavity. 
 
 Obolus (Schmidti.v) celatus (\'olhorth) (]>. 444). 
 
 Specimen figured by Walcott [1898b, PI.- 
 
 Specimen figured by Walcott [1898b, PI. 
 
 Figure 1. E.xterior of ventral valve. U. S. Nat. Mus. Cat. No. 35237a. 
 la. Interior of ventral valve. U. S. Nat. Mus. Cat. No. 3.5237b. 
 
 XXVI, fig. 1] as Obolus (LinguJella) celatus. 
 lb. Exterior of dorsal valve. U. S. Nat. Mus. Cat. No. 35237c. 
 Ic. Interior of dorsal valve. U. S. Nat. Mus. Cat. No. 35237d. 
 
 XXVI, fig. 2] as Obolus (Lingulella) celatus. 
 
 The specimens represented are all from Locality 395, Ujiper Cambrian Obolus sandstone at Joa, near Jegelecht, 
 Eathonia, Russia. 
 
 Obolus (Schmidtia) acitviinatus Mickwitz (p. 442). 
 
 Figure 2. Exterior of ventral valve. U. S. Nat. Mus. Cat. No. 51531a. 
 2a. Interior of ventral valve. U. S. Nat. Mus. Cat. No. 51531b. 
 2b. Exterior of dorsal valve. U. S. Nat. Mus. Cat. No. 51.531c. 
 2c. Interior of dorsal valve. U. S. Nat. Mus. Cat. No. 51531d. 
 
 The specimens represented are all from Locality 395, L'pper Cambrian Obolus sandstone at Joa, near Jegelecht, 
 Esthonia, Russia. 
 
 Obolus (Schmidtia) obtusus Mickwitz (p. 448). 
 
 Figure 3. Exterior of ventral valve. L'. S. Nat. Mus. Cat. No. 51532a. 
 3a. Interior of ventral valve. U. S. Nat. Mus. Cat. No. 51532b. 
 3b. Exterior of dorsal valve. V. S. Nat. Mus. Cat. No. 51532c. 
 3c. Interior of dorsal valve. U. S. Nat. Mus. Cat. No. 51532d. 
 
 The specimens represented are all fiotu Luc 
 Esthonia, Russia. 
 
 ilit\ 
 
 395. Upper Cambrian Obolus sandslone at Joa, near Jegelecht, 
 
 Obolus (Schmidtia) crassus Mickwitz (p. 446). 
 
 Figure 4. Exterior of ventral valve. U. S. Nat. iliis. Cat. No. 51530a. 
 4a. Interior of ventral valve. U. S. Nat. Mus. Cat. No. 51530b. 
 4b. Exterior of dorsal valve. I'. S. Nat. Mus. Cat. No. 51530c. 
 4c. Interior of dorsal valve. U. S. Nat. Mus. Cat. No. 51530d. 
 4d. Interior of an elongate form of a dorsal valve. V. S. Nat. Mus. Cat. No. 51530e. 
 
 The specimens represented are all from Locality 395, I'pper Cambrian Obolus sandstone at Joa, near Jegelecht, 
 Esthonia, Russia. . 
 
 Lingulella (Leptembolox) linguljeformis (Mickwitz) (p. 542). 
 
 Figure 5. A lai^e dorsal \ahe from Locality 396a, pas.sage lieds between the I'pper Cambrian and the Ordovician, 
 "glauconite sandstone," at Lejjpiko, near Leetz. Esthonia, Rtissia. Copied from Mickwitz [1896, 
 PI. Ill, figs. 17a-b]. 
 5a. Small dorsal valve associated with specimen represented by figure 5b. I". S. Nat. Mus. Cat. No. 51537a. 
 5b. Small ventral valve from Locality 395, Upper Cambrian 0&o/»s sandstone at Joa, near Jegelecht, Esthonia, 
 Russia. The beak of this specimen was broken awaj- and has been restored in outline on the figure. 
 U. S. Nat. Mus. Cat. No. 51.537b. 
 52 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XlV 
 
 PRANCES WIESER DEL. 
 
 HEi,iOTr»e CO BOSTON 
 
PLATE XIV. 53 
 
 Obolus apollinis Eichwald (p. 381). 
 
 (Text figs. 4, p. 299, and 1.5, p. 299; and PI. VII, figs. 1-8, 10-17.) 
 
 Figure 6. Exterior of a ventral valve. The portion of the frontal margin anterior to the rrark running through it has 
 been restored. 
 6a. Exterior of a dorsal valve. The portion of the frontal margin anterior to the <ra(k running through it ha.s 
 been restored. 
 
 The specimens represented in iigures 6 and 6a can not now be located. The National Museum records give 
 the locality as 395, Upper Cambrian Obolus sandstone at Joa, near Jegelecht, Esthonia, Russia, and the catalogue 
 number a.s .51-52.5. .Six other specimens with this catalogue number are figured on Plate VII of this monograph. 
 
 Obolus apollinis maximus Mickwitz (p. .384). 
 
 (PI. VII, fig. 9.] 
 
 Figure 7. E.xterior of the central and posterior portions of a dorsal valve that illustrates the character of the outer 
 surface of the numerous layers of the shell. From Locality 395, Upper Cambrian Obolus sandstone 
 at Joa, near Jegelecht, Esthonia, Russia. U. S. Nat. Mus. Cat. No. .51528b. 
 7a. Partly exfoliated broken ventral valve, showing the impression of the main vascular sinuses on one of 
 the inner layers of the shell, also the laminated character and interior markings of the shell. From 
 Locality 336j, Upper Cambrian Obolus sandstone at Staroja Ladoga, Government of Novgorod, Russia. 
 U. S. Nat. Mus. Cat. No. 26924a. 
 
PLATE XV. 
 
 55 
 
PLATE XV. 
 
 h. Central muscle scar. j. Anterior lateral muscle scar. 
 
 Obolus (Mickwitzella) siluricus (Eichwald) (p. 434). 
 
 Figure 1. Exfoliated dorsal valve. U. S. Nat. Mus. Cat. No. 51538a. 
 la. Exfoliated ventral valve. U. S. Nat. Mus. Cat. No. 51538b. 
 lb. Exterior surface of shell. Copied from Mickwitz [1896, PI. Ill, fig. 9]. 
 Ic. Enlargement of surface of ventral valve. U. S. Nat. Mus. Cat. No. 51.538c. 
 
 The specimens represented are all from Locality 396a, passage beds between the Upper Cambrian and the Ordo- 
 vician, "glauconite sandstone," at Leppiko, near Leetz, Esthonia, Russia. 
 
 Obolus (Acritis) axtiquissimus (Eichwald) (p. 4.37). 
 
 I PI. XIII, fig. 3.] 
 
 Figures 2, 2a, and 2b. \'entral, side, and dorsal views of specimen preserving the two valves nearly united. The 
 outer surface of the shell is almost entirely exfoliated. U. S. Nat. Mus. Cat. No. 51534b. 
 
 2c. Photographic enlargement of the exterior surface of the .shell. U. S. Nat. Mus. Cat. No. 51534c. 
 
 2d. Exterior of a partly exfoliated dorsal valve, with the side outline of the two valves united. (_'opied 
 from Mickwitz [1896, PI. Ill, figs. 20a-b.] 
 
 The specimens represented are all from Locality 396d, passage beds between the Upper Cambrian and the Ordo- 
 vician, "glauconite limestone," at Domglint, in Reval. Esthonia, Russia. 
 
 Obolus elegans Mickwitz (p. 390). 
 
 Figure 3. Exterior of a ventral ? valve sho\ving a stronglj^ marked surface. Specimen from Locality 395b, Upper 
 Cambrian Ohohis sandstone at Ilgast. Esthonia. Russia. U. S. Nat. Mus. Cat. No. 5153.5a. 
 
 Obolus (Broggerl\) salteri (Holl) (p. 424). 
 
 ll'l. XIII, figs. 1, la-n.] 
 
 Figure 4. Figure of ventral valve, the type specimen, from Locality 304e, LTpper Cambrian "Black shales" at Coal 
 
 Hill, Malvern Hills, England. Copied from Holl [1865, p. 101, fig. 0]. The figure was also copied 
 
 by Davidson [1866, PI. IV, figs. 28a and 28]. 
 4a and 4b. A'entral and dorsal valves occurring in Locality 310h. Up]ier Cambrian dark argillaceous shale 
 
 somewhere in Sk^ne (Pro^^nces of Malmohus and Christianstad), Sweden. U. S. Nat. Mus. Cat. 
 
 Nos. 14931a and 14931b, respectively. 
 4c. Cast of dorsal valve from Locality 309j, LTpper Cambrian argillaceous shale at Alunbruk, Oeland Island, 
 
 Sweden. U. S. Nat. Mus. Cat. No. 51676a. 
 4d. Partly exfoliated dorsal valve from Locality 309h, Upper Cambrian very dark siliceous limestone at 
 
 Fogelsang, Province of Malmohus, Sweden. U. S. Nat. Mus. Cat. No. 51674a. 
 
 Obolus ? palliatus Barrande (p. 407). 
 
 Figure 5. Exterior surface of dorsal valve, the type specimen, from Locality 303c, passage beds between the Cam- 
 brian and Ordovician, in the suburbs of Ilof, Bavaria, Germany, one-third natural size. Copied 
 from Barrande [lS68a, fig. 65]. 
 
 Obolus? minor Barrande (p. 405). 
 
 Figure 6. Exterior surface of ventral valve, the type specimen, from Locality 303c, passage beds between the Vsim- 
 brian and Ordovician, in the suburbs of Ilof, Bavaria. Germany, one-third natural size. Copied 
 from Barrande [1868a, fig. 68], 
 
 Acrotreta inchoans (Barrande) (p. 690). 
 
 Figures 7 and 7a. Two views copied from Barrande [1868a. figs. 74 and 75] of shells from Locality 303c. i>a,ssage 
 beds between the Cambrian and the Ordovician, suburbs of Ilof, Bavaria, Germany. Figure 7 is 
 the type. 
 56 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XV 
 
 
 ">^rv. 
 
 «' # 
 
 ^^' 
 
 V- ^ 
 
 \ 
 
 
 10 
 
 FRANCES WIESER DEL. 
 
 J 
 
 MCLIOTVPe CO BOSTON. 
 
, PLATE XV. 57 
 
 Obolus? sp. undt. e Kayser (p. 423). 
 
 Figure 8. Ventral valve associated with Eoorlhis saltensis in Locality 389b, Upper Cambrian sandstone at Tilcuya, 
 Province of Jujuy, Argentina. Copied from Kayser |!,S7(i, PI. I, fig. 14]. 
 
 Obolus? sp. undt. f Kayser (p. 423). 
 
 Figure 9. Several valves on small fragment of limestone from Locality 332, Upper CamVjrian at Saimaki, Liaotung, 
 China. Copied from Kayser [1883, PI. Ill, fig. 2]. 
 
 Obolus ? ba various (Barrand«) (p. 385). 
 
 Figure 10. A'entral valve, the type specimen, from Locality 303c, ]3as.sage beds between the Cambrian and Ordo- 
 vician, suburbs of Hof, Bavaria, Germany. Copied from Barrande [1868a, fig. 02], who described 
 it as Lingula buvarica. 
 10a. Dorsal valve associated with the shell represented by figure 10 in Locality 303c. (Copied from Barrande 
 [1868a, fig. 61], who described it as Obolus f palliatus. 
 
 Obolus schmidti Mickwitz (p. 412). 
 
 FiGURE.s lla-c. Exterior, side, and interior views of a dorsal valve, the tj'pe specimen, from Locality 39S, Upper 
 Cambrian Obolus sandstone at Joa, near Jegelecht, Esthonia, Russia. (!'i.ipied from Mickwitz [1896, 
 PI. II, figs. 14a-c]. 
 
 Obolus? murrayi Billings (p. 405). 
 
 Figure 12. Figure of the original type specimen from Locality 314g, Lower Ordovician, Maiden Arm, Hare Bay, 
 northern Newfoundland. Geol. Survey Canada. The specimen is the one on which Billings [186-5, 
 p. 362] based his species, but he did not figure it. 
 
PLATE XVI. 
 
 59 
 
PLATE XVI. 
 
 a. Central lateral space of area, 
 a'. Outer lateral spai-e of area, 
 c. Trapezoidal area, including central, Tniddle 
 
 lateral, and outside lateral muscle scars, 
 h. Central muscle scar. 
 J. Transraedian muscle scar. 
 j. -\nterior lateral muscle scar. 
 
 k. Middle lateral muscle scar. 
 1. Outside lateral muscle scar. 
 p. Pedicle groove. 
 V. \'isceral cavity. 
 vs. Main vascular sinus. 
 X. Heart-shaped cavity. 
 
 ObOLUS (LiNGULOBOLl'S) AFriNI.S (BilHlliJ.s) (p. 431). 
 
 Figure 1. Cast of the interior of a ventral valve showing the characteristic visceral cavity. I". S. Nat. Mus. Cat. 
 
 No. 51679a. 
 la. Cast of a portion of the interior uf a ventral valve. V . S. Xat. Mus. (at. No. .51679b. 
 lb. Cast of the interior of a ventral valve showing the cast of the deep impressions in which the muscle scars 
 
 are situated. V. S. Nat. Mus. Cat. No. ,51679c. 
 Ic. Cast of the interior of a dorsal valve showing the iHisitioii of the central and anterior lateral muscle scars. 
 
 U. S. Nat. Mus. Cat. No. 51079<1. 
 Id. Partly exfoliated dorsal valve showing the area and the varied surface "i tlic inner layers of the shell. 
 
 U. S. Nat. Mus. Cat. No. 51679e. 
 le. Outline of the area of a dorsal valve. V. S. Nat. Mus. Cat. No. ol679f. 
 
 The specimens represented are all from Locality 114b, Lower Ordovician sandstone, 1 mile north of Lance Cove, 
 Great Belle Island, Conception Bay, Newfoundland. 
 
 Obolus (Linguloboll's) spissus (Billings) (\i. 43.2). 
 
 (Pi. XLII,llgs..-!,3a.l 
 
 Figure 2. Dorsal valve from which the outer layers of the shell have been exfoliated so as to show the outline of the 
 
 visceral cavity and vascular sinuses. L'. S. Nat. Mus. Cat. No. ,51678 1. Part of the inner surface 
 
 of this specimen is enlarged on Plate XLII, figure 3a. 
 2a. Cast of the interior of a dorsal valve, on which portions of the shell remain over the muscle scars. I". S. 
 
 Nat. Mus. Cat. No. 51678a. 
 2b. Dorsal valve preserving a portion of the outer surface of the shell, which is enlarged in Plate XLII, 
 
 figure 3. U. S. Nat. Mus. Cat. No. 51678b. 
 2c. Partly exfoliated dorsal valve showing something of the character and arrangement of the inner layers of 
 
 the shell. U. S. Nat. Mus. Cat. No. 51678c. 
 2d. Partly exfoliated dorsal valve illustrating how the impressions of the vascular sinuses and markings are 
 
 preserved on the various layers of the shell. L'. S. Nat. Mus. Cat. No. 51678d. 
 2e. Inner layers of the central portion of a ventral valve, showing the characteristic trapezoidal area and 
 
 vascular sinuses of Obolus. U. S. Nat. Mus. Cat. No. 51678e. 
 2f. Partly exfoliated dorsal valve illustrating peculiarities of the shell not shown by other figures. U. S.Nat. 
 
 Mus. Cat. No. 51678f. 
 2g. Cast of the interior of a dorsal valve with vertical and transverse outline of the convexity of the eheU. 
 
 U. S. Nat. Mus. Cat. No. 51678g. 
 2h. Partly exfoliated dorsal valve that is more elongate than most specimens. V. S. Nat. Mus. Cat. No. 51678h. 
 2i. An unusually well preserved ventral valve, showing the various layers frirming the shell. U. S. Nat. 
 
 Mus. Cat. No. 51678i. 
 2j. Interior of a ventral valve as shown by the impression made on the laminated inner layers of the shell, 
 
 the outer layers being exfoliated. V. S. Nat. Mus. Cat. No. 51678J. 
 2k. Cast of the interior of a ventral valve, showing muscle scars and va.-^cular markings essentially the same 
 
 as those of Obolus. V. S. Nat. Mus. Cat. No. 51678k. 
 
 The specimens represented are all from Locality 114b, Lower Ordovician sandstone, 1 mile north <if Lance Cove, 
 Great Belle Island, Conception Bay, Newfoundland. 
 60 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH U PL. XVI 
 
 FRANCES WIESER DEL. 
 
 vpe CO aosTOM 
 
PLATE XVII, 
 
 61 
 
PLATE XVII. 
 
 a. Tentral laleral space of area. m. Pedicle muscle scar, 
 a'. Outer latenil space of area. p. Pedicle groove. 
 
 c. Trapezoidal area, including central, ps. Parietal band. 
 
 middle lateral, and outside lateral s. Median septum. 
 
 muscle scars. v. Visceral cavity. 
 
 f. Fle.xure line of area. vs. Main vascular sinus. 
 
 g. Umbonal muscle scar. ivs. Lateral branches of vascular system, 
 h. Central muscle scar. pvs. Peripheral branches of the vascular 
 
 i. Transmedian muscle scar. system, 
 
 j. Anterior lateral muscle scar. x. Heart-shaped cavity, 
 
 k. Middle lateral muscle scar. z. Same as ivs of the ventral valve. 
 
 I. Outside lateral and middle lateral 
 muscle scars. 
 
 LiNGULELLA ACUTANGULA (Roemcr) (p. 474). 
 
 Figure 1. Ventral valve in limestonp, from which the shell is partly exfoliated. Locality 69, Upper Cambrian, 
 
 Honey Creek, Burnet County, Texas. V. S. Nat. Mus. Cat. No. 27412a. The area of this shell is 
 
 enlarged in figure Irl. 
 la. Cast of the interior of a ventral valve from Locality 353c, Upper Cambrian sandstone, Llano County, Texas, 
 
 showing concentric lines of tubercles that fill the punctae of the interior surface of the shell. U. S. 
 
 Nat. Mus. Cat. No. 35240a. The area of this shell is enlarged in figure lb. 
 lb. Enlargement of cast of area and pedicle groove of figure la. U. S. Nat. Mus. Cat. No. 35240a. 
 Ic. Cast of interior of ventral valve, from same locality as the specimen represented in figiu-cs la and lb, in 
 
 which the cast of the \-isceral cavity and muscle scars is unusually prominent. V. S. Nat. Mus. Cat. 
 
 No. 3.5240b. Copied from Walcott [1898b, PI. XX\'II, fig. 6]. 
 Id. Enlargement of the cast of the area of the specimen represented by figure 1. V. S. Nat. Mus. Cat. No. 
 
 27412a. 
 le. Ventral valve in sandstone from Locality 68, Upper Cambrian, Packsaddle Mountain, Llano County, 
 
 Texas. U. S. Nat. Mus. Cat. No. 27410a. 
 If. Cast of the interior of a ventral valve showing the muscle scars unusually well preserved. Locality 353c, 
 
 Upper Cambrian sandstone, Llano County, Texas. U. S. Nat. Mus. Cat. No. 35240c. Copied from 
 
 Walcott [1898b, PI. XXVIII, fig. 1]. 
 Ig. Cast of the interior of a ^•entral valve from Locality 69, Upper Cambrian limestone. Honey Creek, Bimiet 
 
 County, Texas. U. S. Nat. Mus. Cat. No. 27412b. 
 Ih. Cast of the interior of a dorsal valve from Locality 3f-3c, Upper Cambrian sandstone, Llano County, Texas, 
 
 in which the interior lateral branches (?.) of th > vascular system are shown. U. S. Nat. Mus. Cat. 
 
 No. 35240d. Copied from Walcott [189Sb, PI. XXVIII, fig. 2]. 
 li. Cast of the interior of a dorsal valve from Locality 69, Upper Cambrian limestone, Honey Creek, Burnet 
 
 County, Texas. U. S. Nat. Mus. Cat. No. 27412c. 
 Ij. Cast of the interior of a dorsal valve which shows that the punctate surface of the interior of the shell did 
 
 not extend to the outer border. From Locality 353c, tapper Cambrian sandstone, Llano County, 
 
 Texas. U. S. Nat. Mus. Cat. No. 35240e. 
 Ik. Cast of the interior of a dorsal valve from Localitj- 68e, Upper Cambrian sandy limestone, Packsaddle 
 
 Mountain, Llano County, Texas. U. S. Nat. JIus. Cat. No. 27410b. 
 11. Enlargement of a portion of a ventral valve showing the outer surface in front of the line a" a" and the 
 
 surface of one of the inner layers of the shell back of a" a". I'. S. Nal. Mus. The specimen from 
 
 which this figure was drawn can not be located; even the locality is unknown. 
 Im. Median, longitudinal, thin section through the central portion of a ventral ^alve; os=thin outer layer 
 
 without traces of structure; is=obliquely laminated inner layer; il=interior lamellas produced 
 
 by the thickening of the shell. U. S. Nat. Mus. Cat. No. 27410c. 
 In. Central portion of a transverse median thin section; os=thin outer layer; i.«=obliquely laminated inner 
 
 layer. U. S. Nat. Mus. Cat. No. 27410d. 
 lo. Median longitudinal section through the posterior portion of a vintral valve. Lettering same as for figure 
 
 Im. U. S. Nat. Mus. Cat. No. 27410e. 
 
 The specimens thin-sectioned for reproduction in figures Im, In, and lo came from I.cnality 68e, Upper Cambrian 
 sandy limestone, Packsaddle Mountain, Llano County, Texas. 
 62 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XVII 
 
 FRANCES WtESEH DEL. 
 
 HEUIQTYPC CO aOSTOM 
 
PLATE XVIII. 
 
 63 
 
PLATE XVIII. 
 
 a. Central lateral space of area. j. Anterior lateral muscle scar, 
 
 a'. Outer lateral space of area. p. Pedicle groove, 
 
 f. Flexure line of area. v. Visceral cavity. 
 
 h. Central muscle scar. vs. Main vascular sinu^. 
 
 LlNGULELL.A. MOSI.V (Hall) (p. 5'2()). 
 
 Figure 1. Cast showing part of the interior of a ventral valve from Locality 85s, Tppt-r < ambrian sandstone at Prairie 
 
 du Sac, Wisconsin. U. S. Nat. Miis. Cat. No. 27370a. 
 la. Cast of a compressed ventral valve from Locality 85x, I'pper Camliriaii sandstone near Mazomanie, 
 
 Wisconsin. U. S. Nat. Mus. Cat. No. 27373a. 
 lb. Cast of a ventral valve from Locality 78s, L^pper Cambrian sandstone in suburbs of Osceola, Wisconsin. 
 
 U. S. Nat. Mils. Cat. No. 27371a. 
 Ic. Cast of the interior of a compressed specimen of a ventral valve, showing traces of the interior markings. 
 
 Locality S85x, I'pper Cambrian sandstone near Jlazomanie, Wisconsin. U. S. Nat. Mus. Cat. No. 
 
 27373b. 
 Id. Cast of the interior of a dorsal valve from Locality 78s, L'pper Cambrian sandstone near Osceola, ^\'b- 
 
 consin. U. S. Nat. Mus. Cat. No. 27371b. 
 le. Cast of a more elongate dorsal valve from Locality 78, Upper Cambrian sandstone near Osceola, \\'is- 
 
 consin. L'. S. Nat. Mus. Cat. No. 27371c. 
 If. Cast of a dorsal valve that is much broader posteriorly than most dorsal valves of the species. Locality 86, 
 
 L'pper Cambrian sandstone at Gibraltar Bluff, Lodi, Wisconsin. U. S. Nat. Mus. Cat. No. 27372a. A 
 
 specimen from Locality S85x (Cat. No. 27373c) was used to restore portions of this figiu'e. 
 
 LiNGULELLA MOSIA OSCEOLA (Walcott) (p. 521). 
 
 Figure 2. Cast of a ventral valve, the type specimen, from Locality 78, L'pper Cambrian sandstone near Osceola, 
 
 Wisconsin. I^. S. Nat. Mus Cat. No. 27327a. 
 2a. Cast of ventral valve from Locality 78s, Upper Cambrian sandstone near Osceola, Wisconsin. U. S. Nat. 
 
 Mus. Cat. No. 27327b. 
 2b. Enlargement of the area of the cast of a ventral valve, associated with the specimen represented by figure 2. 
 
 U. S. Nat. Mus. Cat. No. 27327c 
 2c. Cast of a dorsal valve associated with the ventral valve represented by figure 2 U. S. Nat. Mus. Cat. No. 
 
 27327d. 
 
 LiNGULELLA WINOXA (Hall) (p. 539). 
 
 Figure 3. Cast of ventral valve from Locality 78c, L'pper Cami>riau sandstone at O.'sceola, Wisconsin. I'. S. Nat. 
 Mus. Cat. No. 27400a. 
 
 3a. Partly exfoliated ventral ^■alve from Locality 85s, l'pper Cambrian sandstone at Prairie du Sac, Wis- 
 consin. U. S. Nat. Mus. Cat. No. 33856a. 
 
 3b. Partly exfoliated dorsal valve, associated with the specimen represented by figure 3a. I'. S. Nat. Mus. 
 Cat. No. 33856b. 
 
 LiNGULELLA WINOXA CONVEXA (Walcott) (p. 540). 
 
 Figure 4. Two ventral valves, natural size, from Locality S85x, Upper Cambrian sandstone near Mazomanie, 
 Wisconsin. U. S. Nat. Mas. Cat. No. 51854a. 
 
 4a and 4b. Casts of \entral valves showing area. Locality 78, Upper Cambrian sandstone near t)sceola. 
 Wisconsin. L'. S. Nat. Mus. Cat. Nos. 3523-5a and 3.5235b, respectively. Figure 4a represents the 
 type specimen. 
 
 4c. Cast of the usual form of dorsal \al\e. Same locality as specimen represented by figure 4a. U. S. Nat. 
 Mus. Cat. No. 35235c. 
 
 4d. Cast of an elongate form of dorsal valve, showing central and anterior lateral Bcaxa. Same locality as speci- 
 men represented by figure 4a. U. S. Nat. Mus. Cat. No. 3.5235d. 
 64 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XVIl- 
 
 FRANCES WIESER DEL. 
 
 MELIOTVf'E CO OOSTOw 
 
PLATE XVIII. 65 
 
 LlKGULELLA OWENI (Walcott) (p. 523). 
 
 FiouHE 5. Ventral valve showing the exterior surface of the shell, from Locality 86, Upper Cambrian sandstone at 
 
 Gibraltar Bluff, Lodi, Wisconsin. U. S, Nat. Mus. Cat. No. 25330a. 
 5a. Enlargement of the area of a cast of a flattened ventral valve in which all traces of a flexure line have been 
 
 lost. Locality 86s, Upper Cambrian sandstone at Prairie du Sac, Wisconsin. U. S. Nat. Mus. Cat. 
 
 No. 27385a. 
 5b. Cast of the interior of a dorsal valve, the type specimen, associated with the specimen represented by 
 
 figure 5. U. S. Nat. Mus. Cat. No. 25330b. 
 5c. A smaller and less elongate dorsal valve than that represented by figure 5b, but from the same locality. 
 
 U. S. Nat. Mus. Cat. No. 25330c. 
 5d and 5e. Casts of small ventral valves from Locality 78c, Upper Cambrian sandstone at Osceola, Wis- 
 consin. U. S. Nat. Mus. Cat. Nos. 27329a and 27329b, respectively. . 
 5f. Cast of a dorsal valve from same locality as specimens represented by figures 5d and 5e. U. S. Nat. Mus. 
 
 Cat. No. 27329c. 
 
 Obolus discoideus (Hall and Whitfield) (p. 389). 
 
 Figure 6. Exteriorof a partly exfoliated ventral valve. U. S. Nat. Mus. Cat. No. 24555a. 
 
 6a. Dorsal valve, partly exfoliated. U. S. Nat. Mus. Cat. No. 245.55b. 
 
 6b and 6c. Probably ventral valves, but it is difficult to determine owing to the rounding of the posterior 
 portion of the valve. V. S. Nat. Mus. Cat. Nos. 24555c and 24555d, respectively. Figure 6c is drawn 
 from the type specimen figured by Hall and WTiitfield [1877, PI. I, fig. 2]. The specimen repre- 
 sented by their figure 1 is not redrawn in this monograph. 
 
 The specimens represented by figures 6, 6a-c are all from Locality 313j, Upper Cambrian limestone in the Eureka 
 district, Nevada. 
 
 Figure 6d. Partly exfoliated dorsal valve, showing outline of visceral area, from Locality 62, Upper Cambrian 
 Dunderberg shale, north of Adams HUl, Eureka district, Nevada. U. S. Nat. Mua. Cat. No. 51547a. 
 62667°— VOL 51, pt 2—12 5 
 
PLATE XIX. 
 
 67 
 
PLATE XIX. 
 
 h. Central muscle scar. v. Visceral cavity. 
 
 j. Anterior lateral muscle scar. vs. Main vascular sinus. 
 
 s. Median septum. 
 
 LiNGULELLA BELLULA (Walcott) (p. 482). 
 
 FiGURR 1. Cast of a ventral valve from Locality 114, Upper Camlirian upper sandstone beds of Little Belle Island, 
 
 Conception Bay, Newfoundland. U. S. Nat. Mus. Cat. No. 27309a. 
 la. Cast of the interior of a small ventral valve, the type epecimen, from Locality 114a, Upper Cambrian 
 
 arenaceous shales about 50 feet below the sandstone of Locality 114, Little Belle Island, Conception 
 
 Bay, Newfoundland. U. S. Nat. Mus. Cat. No. r)7082a. 
 lb. Cast of the interior of a ventral valve associated with the specimen represented by figure la. U. S. Nat. 
 
 Mus. Cat. No. 57082b. 
 Ic. Cast of the interior of a dorsal valve, showing the arching of the parietal band outward to the main vascular 
 
 sinus, associated in the shale with specimen represented by figure la. U. S. Nat. Mus. Cat. No. 57082c. 
 Id. Cast of the interior of a dorsal valve, showing the median septum and what may be the central muscle 
 
 scars, associated in the shale with specimen represented by figure la. U. S. Nat. Mus. Cat. No. 57082d. 
 le. Interior of a dorsal valve associated with the specimen represented by figure la. U. S. Nat. Mus. Cat. 
 
 No. 57082e. 
 
 LiNGULELLA BELLA (Walff)tt) (j). 481). 
 [PI. XXXVI, fig. 4.] 
 
 FiciuRE 2. Cast of the interior of a ventral valve from Locality 114a, Upper Cambrian arenaceous shale beneath tho 
 
 upper sandy beds on Little Belle Island, Conception Bay, Newfoundland. U. S. Nat. Mus. Cat. No. 
 
 27307a. 
 2a. Cast of the interior of a ventral valve, associated with specimen represented by figure 2, but which is 
 
 more strongly marked by concentric and radiating striae. U. S. Nat. Mus. Cat. No. 27307b. 
 2b. Cast of the interior of a dorsal valve, the area of which, owing to fracture, slightly resembles the area of a 
 
 ventral valve. From the same bed and locality as specimen represented by figure 2. Y. S. Nat. 
 
 Mus. Cat. No. 27307c. 
 2c. A somewhat broader dorsal valve than that represented by figure 2b, but associated in the same bed with 
 
 it. U. S. Nat. Mus. Cat. No. 27307d. 
 2d. Cast of the interior of a ventral valve from Locality 114b, Lower Ordovician sandstone 1 mile north of 
 
 Lance Cove, Great Belle Island, Conception Bay, Newfoundland. U. S. Nat. Mus. Cat. No. 27308a. 
 2e. Finely preserved dorsal valve, associated in the same bed with specimen represented by figure 2d. U. S. 
 
 Nat. Mus. Cat. No. 27308b. 
 2f. Cast of the interior of a convex ventral valve from Locality 114, Upper Cambrian upper sandstone beds 
 
 of Little Belle Island, Conception Bay, Newfoundland. IT. S. Nat. Mus. Cat. No. 57081a. 
 2g. Enlargement of a cast of the area of a dorsal valve, associated in the bed with specimens represented by 
 
 figures 2d and 2e. U. S. Nat. Mus. Cat. No. 27308c. 
 2h. Finely preserved ventral and dorsal valves from which the thin outer surface has been exfoliated, the 
 
 type specimen, associated in the same bed with specimen represented by figure 2d. U. S. Nat. Mus. 
 
 Cat. No. 27308d. 
 2i. Dorsal valve from Locality 114b, see figure 2d. U. S. Nat. Mus. Cat. No. 27308e. 
 2j. Cast of the interior of a ventral valve, natural size, from Locality 114b, see figure 2d. U. S. Nat. Mus. 
 
 Cat. No. 27308f. 
 2k and 21. Exterior of ventral valves from Locality 114b, sec figure 2d. U. S. Nat. Mus. Cat. Nos. 27308g 
 
 and 27308h, respectively. 
 2m. Dorsal valve. U. S. Nat. Mus. Cat. No. 27308i. 
 2n. D.irsal valve. V. S. Nat. Mus. Cat. No. 27308J. 
 2o. Dorsal valve. U. S. Nat. Mus. Cat. No. 27308k. 
 2p. Dorsal valve. U. S. Nat. Mus. Cat. No. 27.308 1. 
 2q. Dorsal valve. U. S. Nat. Mus. Cat. No. 27308m. 
 
 Figures 2i, 2m-q illustrate variations in the size and outline of dorsal valves from LiH-ality 114b, Lower Ordovician 
 sandstone, 1 mile north of Lance Cove, Great Belle Island, Conception Bay, Newfoundland. 
 08 
 
o S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XIX 
 
 FRANCES WIE3ER DEL. 
 
 
PLATE XIX. 69 
 
 LiNGULELLA ELLSI (Walcott) (j). 49.5). 
 
 Figure 3. Ventral valve, the type specimen, slightly distorted by compressidn, showing the area. 11. S. Nat. Miis. <]at. 
 
 No. 2731.5a. 
 3a. Cast of a ventral valve, .showing the area and outlines of the visceral cavity. U. S. Nat. Mus. Cat. No. 
 
 27315b. 
 3b. Dorsal valve crushed down into the ventral valve. U. S. Nat. Mus. Cat. No. 2731.5c. 
 3c. Dorsal valve slightly distorted by compression. U. S. Nat. Mus. Cat. No. 2731.5d. 
 
 The specimens represented are all from Locality 220a, Ordovician .siliceou.s shales at the Grand Trunk railroad 
 bridge over Chaudiere River, Quebec, Canada. 
 
 LiNGULELLA L^vis Mattliew (p. 512). 
 
 Figure 4. A large dorsal valve, the type specimen. University of Toronto, Canada. Specimen figured by Ma'thew 
 
 [1892, PI. XII, fig. 4b], 
 4a. Ventral valve flattened in .shale. University of Toronto, Canada. Specimen figured by Matthew [1892, 
 
 PI. XII, fig. 4a]. 
 4b. Ventral valve flattened in the shale. University of Toronto, Canada. 
 
 The specimens represented are all from Locality 301n, Upper Cambrian shales near the falls at St. John, New 
 Brunswick. 
 
 LiNGULELLA L^vis GRANDis Matthew (p. .512). 
 
 Figure 4c. Ca.st of the interior of a dorsal valve from Locality 325b, Upper Cambrian shale at Escasonie Shore, East 
 Bay, Cape Breton, Nova Scotia. University of Toronto, Canada. Specimen figured by Matthew 
 [1903, PI. XV, fig. Id]. 
 
 LiNGULELLA (LiNGULEPis) SPATULA (Walcott) (]). 5.58). 
 
 Figure .5. Nearly perfect ventral valve, the type specimen, from which the outer surface has been exfoliated. U. S. 
 
 Nat. Mus. Cat. No. 35290a. 
 5a. Dorsal valve preserving concentric and radiating stria? beneath the outer stirface. U. S. Nat. Mus. Cat. No. 
 
 35290b. 
 5b. Cast of the dorsal valve, showing cast of median ridge and pits on the inner surface. U. S. Nat. Mus. Cat. 
 
 No. 35290c. 
 
 The specimens represented are all fr<]ni Locality 74d, Middle (^ambrian sandstones in Bass (."anyon. Grand Canyon 
 of the Colorado, Arizona. 
 
PLATE XX. 
 
 71 
 
PLATE XX. 
 
 h. Central muscle scar. v. Visceral cavity. 
 
 j. Anterior lateral muscle scar. • vs. Main vascular sinus. 
 
 8. Median septum. x. Ilearl-sliaped cavity. 
 
 LlNGULELLA MANTICULA (Wllite) (p. 517). 
 
 Figure 1. Cast of the interior of a ventral valve from Locality 313f, Upper Cambrian limestone at Schellboume, 
 
 Schell Creek Range, Nevada. U. S. Nat. Mus. Cat. No. 8569a. 
 la. Dorsal valve associated on the same hand specimen with the valve represented by figure 1. I'. .S. Xat. 
 
 Mus. Cat. No. 85G9b. 
 lb. <'a8t showing part of the interior of a more elongate dorsal valve than that represented by figure la, but 
 
 associated on the same hand specimen with it. U. S. Nat. Mus. Cat. No. 8569c. 
 Ic. Type specimen, the ventral valve, from the locality represented by figures 1, la-l>. l'. S. Nat. Mus. 
 
 Cat. No. 8569d. When the plates were made up this specimen could not be located and the original 
 
 drawing prepared for White [1877, PL III, fig. 2b] was used. The specimen has been found on the 
 
 same hand specimen with the type of Acrotreta pyxidicula. 
 
 Obolus rotundatus (Walcott) (p. 411). 
 
 Figure 2. A ventral valve, the type specimen, from Locality 313d, Lower Ordovician limestone near Schellboume, 
 
 Schell Creek Range, Nevada. U. S. Nat. Mus. Cat. No. 27337a. 
 2a. Cast of the interior of a dorsal valve associated with the shell represented by figure 2. U. S. Xat. Mus. 
 
 Cat. No. 27337b. 
 2b. Ventral valve from Locality 160a, I'pper Cambrian limestone, west of Bear Creek, south of (Jallatin 
 
 Valley, Montana. IT. S. Nat. Mus. Cat. No. 27338a. 
 2c. A small but very perfect ventral valve associated with the valve represented by figure 2b. V . S. Nat. 
 
 Mus. Cat. No. 27338b. 
 2d. A small and characteristic dorsal valve associated with the valves represented by figures 2b and 2c. U. iS. 
 
 Nat. Mus. Cat. No. 27338c. 
 2e. Dorsal valve from Locality 302b, Middle Cambrian limestones near Crowfoot Ridge, Yellowstone National 
 
 Park, Wyoming. U. S. Nat. Mus. Cat. No. 35207a. Specimen figured by W'alcott [1899, PI. LX, 
 
 fig. 2a] as the dorsal valve of Obolus (Lingulella) desideratus. (See description of fig. 4, below.) 
 
 LiNGULELLA POGONIPENSIS (Walcott) (p. 525). 
 
 Figure 3. Ventral valve, the type specimen, showing cast of the area and the pedicle furrow. U. S. Xat. Mus. 
 Cat. No. 27332a. 
 3a. Small, partly exfoliated ventral valve. U. S. Nat. Mus. Cat. No. 27332b. 
 3b. Partly exfoliated dorsal valve. U. S. Nat. Mus. Cat. No. 27332c. 
 3c. Partly exfoliated ventral valve. U. S. Nat. Mus. Cat. No. 27332d. 
 The specimens represented are all from Locality 201, passage beds between the Upper Cambrian and the 
 Ordovician, in the ridge east of Hamburg Ridge, Eureka district, Nevada. 
 
 Lingulella desiderata (Walcott) (p. 492). 
 
 Figure 4. Partly exfoliated ventral valve from Locality 302 I, Upper Cambrian limestone, Gallatin Range, Yellow- 
 stone National Park, Wyoming. U. S. Nat. Mus. Cat. No. 33867a. Type specimen, figured by 
 Walcott [1899, PI. LX, fig. 2] as Obolus (Lingulella) desideratus. (See description of fig. 2e, above.) 
 
 4a. Dorsal valve, associated with the specimen represented by figure 4. U. S. Nat. Mus. Cat. No. 33S67b. 
 
 4b and 4c. Ventral and dorsal valves on the ,'iamo piece of limestone from Locality 81, Upper Cambrian, near 
 the Hamburg mine. Eureka district, Nevada. U. S. Nat. Mus. Cat. Nos. 27313a an<l 27313b, 
 respectively. 
 
 5 and 5a. Ventral valves from Locality 94xx, Middle Cambrian shaly limestones at Givens Mill, on Cowan 
 Creek, Cherokee County, Alabama. U. S. Nat. Mus. Cat. Nos. 27355a and 27355b, respectively. 
 
 5b. Ventral valve from Locality 93o, Upper Cambrian shales near Jordans, on Cowan Creek, Cherokee 
 Covmty, Alabama. U. S. Nat. Mus. Cat. No. 56990a. 
 
 5c. Dorsal valve, slightly distorted in outline, from Locality 94o, Upper Cambrian shale near Givens Ford, 
 on Cowan Creek, Cherokee County, Alabama. U. S. Nat. Mus. Cat. No. 56991a. 
 72 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XX 
 
 FRANCES WIESER DEL. 
 
 L'OTVPt CO 006TON 
 
PLATE XX. 73 
 
 LiNGXiLELLA DESIDERATA (Walcott) — Continued. 
 
 Figure 5d. X'entral valve from Locality 96, Upper Cambrian limestone near Rome, Floyd County, Georgia, marked 
 
 by unusually strong concentric striae. U. S. Nat. Mus. Cat. No. 51823a. 
 5e. Dorsal valve associated with the ventral valve illustrated by figure 5d. U. S. Nat. Mus. Cat. No. 51823b. 
 5f and 5g. Dorsal valves from Locality 107a, Upper Cambrian shaly limestone near Copper Ridge, 11 miles 
 
 northwest of Knoxville, Tennessee. U. S. Nat. Mus. Cat. Nos. 27312a and 27312b, respectively. 
 5h. Large ventral valve from Locality 93, I'pper Cambrian shales near Jordans on Cowan Creek, Cherokee 
 
 County, Alabama, referred to this species with some doubt. U. S. Nat. Mus. Cat. No. 56990b. 
 5i. Broad dorsal valve from Locality 93a, Upper Cambrian shales on the Terrapin Creek road from Center to 
 
 Amberson, Cherokee County, Alabama, that is doubtfully referred to this species, although there 
 
 is considerable difference in the form of the shell in most localities at which it occurs. U. S. Nat. 
 
 Mus. Cat. No. 51841a. 
 5j. Form similar to that in figure 5i, from Locality 302b, Upper Cambrian limestone near Crowfoot Ridge, 
 
 Yellowstone National Park, Wyoming. U. S. Nat. Mus. Cat. No. 27311a. Specimen figured by 
 
 Walcott [1899, PI. LX, fig. 3] as Dicellomus nanus. 
 
 LlNGULELLA PUNCTATA (Walcott) (p. 528). 
 
 Figure 6. Partly exfoliated ventral valve from Locality 58, Middle Cambrian Secret Canyon shale, Secret and New 
 York canyons, Eureka district, Nevada, showing cast of part of the interior surface of the shell. U. S. 
 Nat. Mus. Cat. No. 27335a. Type specimen, figured by Walcott [1884b, PL IX, fig. 3] as Lingulaf 
 manticula. 
 6a. Parti v exfoliated dorsal valve associated in the same piece of limestone with the specimen represented 
 by figure 6. U. S. Nat. Mus. Cat. No. 27335b. Specimen figured by Walcott [1884b, PL XI, fig. 8] 
 as Lingula ? manticula. 
 
PLATE XXI. 
 
 75 
 
PLATE XXI. 
 
 f. Flexure line of area. p. Pedicle groove. 
 c. ITmbonal muscle scar. s. Median septum, 
 
 h. Central muscle scar. v. Visceral cavity. 
 
 j. Anterior lateral muscle scar. vs. Main va.scular sinus. 
 
 LiNGULELLA PERATTENUATA (Whitfield) (p. 523). 
 
 Figure 1. Cast of the interior of a ventral valve from Locality 355, Middle (anibriaii .sandstones on Red Canyon Creek, 
 
 Black Hills, South Dakota. U. S. Nat. Mus. Cat. No. 27423a. 
 la. Cast of the interior of a ventral valve from Locality 74, Middle Cambrian sandstone, head of Nunkowf ap 
 
 Valley, Grand Canyon of the Colorado, Arizona. U. S. Nat. Mus. Cat. No. 51796a. 
 lb. Narrow, partly exfoliated ventral valve, with the apex rounded, from Locality 355, Middle Cambrian 
 
 sandstones on Red Canyon Creek, Black Hills, South Dakota. U. S. Nat. Mus. Cat. No. 24589a. 
 
 Type specimen, figured by Whitfield [1880, PI. II, fig. 9] as Lingulepis peratlenuatiis. 
 Ic. Cast of the interior of a ventral valve associated with the valve represented by figure 1. U. S. Nat. Mus. 
 
 Cat. No. 27423b. This specimen occurs on the same hand specimen with figured specimens of Lin- 
 
 gulella (Lingulepis) acuminata. 
 Id. Cast of the interior of a dorsal valve associated with the valves represented by figures 1 and Ic. U. S. Nat. 
 
 Mus. Cat. No. 27423c. 
 le. Cast of the interior of a ventral valve from Locality 67c, Upper Cambrian sandstone, Tatur Hill, Burnet 
 
 County, Texas. U. S. Nat. Mus. Cat. No. 27424a. 
 If. Partly exfoliated dorsal valve from Locality 68y, Upper Cambrian .sandstone, Packsaddle Mountain, Llano 
 
 County, Texas. U. S. Nat. Mus. Cat. No. 27422a. 
 Ig. Partly exfoliated dorsal valve a-ssociated with the valve represented by figure If. U. S. Nat. Mus. Cat. 
 
 No. 27422b. 
 Ih. Cast of the interior of a dorsal valve associated on the same hand specimen with the valve represented by 
 
 figure lb. U. S. Nat. Mus. Cat. No. 24589b. Specimen figured by Whitfield [1880, PI. II, fig. 8] a.s 
 
 Lingulepis perattenuatus. 
 li. Cast of the interior of a dorsal valve associated with the valves represented by figiu-es lb and Ih. U. S. Nat. 
 
 Mus. Cat. No. 24.589c. Specimen figured by Whitfield [1880, PI. II, fig. 7] as Lingulepis perattenuatus. 
 
 LiNGXJLELLA SIMILIS (Walcott) (p. 532). 
 
 FIGURE 2. Cast of the interior of a ventral valve, the type specimen, from Locality 88a, Middle Cambrian limestone, 
 near Dcadwood, Black Hills, South Dakota. U. S. Nat. Mus. Cat. No. 27.339a. 
 
 2a. Cast of the interior of a dorsal valve a.ssociated with the specimen represented by figure 2. U.S. Nat. Mus. 
 Cat. No. 27339b. 
 
 2b and 2c. Partly exfoliated ventral and dorsal valves, respectively, associated with the specimens repre- 
 sented by figures 2 and 2a. IT. S. Nat. Mus. Cat. Nos. 27339c and 27339d, respectively. 
 
 2d. Small, strongly convex dorsal? valve doubtfully referred to this species, from same locality and bed of 
 limestone as the specimens represented by figures 2, 2a-c. U. S. Nat. Mus. Cat. No. 27339e. 
 
 2e. Cast of the interior of an unusually convex, elongate ventral valve. U. S. Nat. Mus. Cat. No. 27340a. 
 
 2f. Cast of the interior of a ventral valve that narrovTs toward the frontal margin. U. S. Nat. Mus. Cat. No. 
 27340b. 
 
 2g and 2h. Casts of two dorsal valves that show variation in outline. U. S. Nat. Mus. Cat. Xo.s. 27340c and 
 27340d, respectively. 
 
 2i and 2j. Casts of associated ventral and dorsal valves that approach most closely the typical forms from the 
 Black Hills. U. S. Nat. Mus. Cat. Nos. 27340e and 27340f, respectively. 
 
 The specimens from which figures 2e to 2j are drawn are all from Locality 97a, I "pper Cambrian sandstone, at ^^'in- 
 field, Wisconsin. 
 
 Figures 3 and 3a. Casts of the interior of ventral valves from Locality 106, .Middle Cambrian .shaly s;indstones of the 
 Rome formation, in Bays Mountains, 10 miles (16.1 km.) southeast of Knoxville, Tennessee. U. S. Nat. 
 Mus. Cat. Nos. 27367a and 27367b, respectively. 
 3b. Cast of the interior of a ventral valve from Locality 10a, Middle Cambrian, at the same general locality as 
 
 the specimens represented by figures 3 and 3a. U. S. Nat. Mus. Cat. No. 27326a. 
 3c and 3d. Casts of the int; rior of dorsal valves associated with the ventral valves represented by figures 3 and 
 3a. U. S. Nat. Mus. Cat. Nos. 27367c and 27367d, respectively. 
 76 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XXI 
 
 vy 
 
 
 ^1 
 
 V 
 
 ''/j'-t-J «s.^^V» 
 
 
 y^^Vt^ 
 
 
 4a 
 
 hNCES 
 
 WIESER DEL. 
 
 HCklOTVPC CO BOSTON. 
 
PLATE XXI. 77 
 
 LiNGULELLA (LiNGULEPIS) ROWEI (Walcott) (p. 558). 
 
 Figure 4. Exfoliated ventral valve, the type specimen. U. S. Nat. Mus. Cat. No. 51897a. 
 4a. Exfoliated dorsal valve. U. S. Nat. Mius. Cat. No. 51897b. 
 4b. Enlargement of the outer surface of another specimen. U. S. Nat. Mus. Cat. No. 51897c, 
 
 The three specimens from which figures 4, 4a-b are drawn are from Locality 14p, Lower Cambrian limestone near 
 Resting Springs, Inyo County, California. 
 
 LiNGULELLA RANDOMENSIS (Walcott) (p. 530). 
 
 Figure 5. Ventral valve, the type specimen, showing the cast of the area and pedicle groove. U. S. Nat. Mus. Cat. 
 No. 35208a. 
 5a. Dorsal valve associated with specimen represented by figure 5. U. S. Nat. Mus. Cat, No. 35208b, 
 
 The specimens represented are both from Locality 6y, Upper Cambrian, on the north side of Random Island, be- 
 tween Birch and Sandy points. Smith Sound, Trinity Bay, Newfoundland, 
 
 LiNGULELLA SCHUCHERTI (Walcott) (p. 530). 
 
 Figure 6. Cast of a ventral valve, the type specimen, showing the area and pedicle furrow, from Locality 367, Low^r 
 Cambrian limestone, Troy, Rensselaer County, New York, U, S, Nat, Mus, Cat, No, 51775a, 
 
PLATE XXII. 
 
 79 
 
PLATE XXII. 
 
 a. Central lateral space of area, 
 a'. Outer lateral space of area, 
 c. Trapezoidal area, including central, middle 
 
 lateral, and outside lateral inascle scars. 
 f. Flexure line of area, 
 h. Central muscle scar. 
 
 i. Transmedian mu-scle scar. 
 
 j. .\nterior lateral rnascle scar, 
 ps. Parietal band. 
 
 V. Visceral cavity. 
 vs. Main vascular sinas. 
 
 X. Heart-shaped cavity. 
 
 LiNGULELLA GRANVILLEN.SI.S Walcott (p. 504). 
 
 Figure 1. Exterior of partly exfoliated ventral valve from Locality 38a, Lower Cambrian limestone, 2 miles south of 
 North Granville, Washington County, New York. U. S. Nat. Mus. Cat. No. 17440a. Type speci- 
 men, figured by Walcott [1887, PI. I, fig. 15b; and 1891a, PI. LXVII, fig. 4b]. The specimen 
 figured by Walcott [1887, PI. I, fig. 15c; and lS91a, PI. LXVII, fig. 4c] is not refigured in this mono- 
 graph. It is in the collections of the I'nited States National Museum, Catalogue No. 17440e. 
 
 la. Exterior of partly exfoliated ventral valve associated with the valve represented by figure 1. U. S. 
 Nat. Mus. Cat. No. 17440b. 
 
 lb. Interior of a small ventral valve from Locality 37b, Lower Cambrian, one-fourth mile ea.-<t of Salem, Wash- 
 ington County, New York, showing the visceral cavity and main vascular sinuses. U. S. Nat. Mus. 
 Cat. No. 52036a. 
 
 Ic. Exterior of a partly exfoliated dorsal valve associated with the valve represented by figure.-) 1 and la. 
 U. S. Nat. Mus. Cat. No. 17440c. Specimen figured by Walcott [1887, PI. I, fig. 15; and 1891a, PI. 
 LXVII, fig. 4]. 
 
 Id. Cast of the interior of a dorsal valve associated with the valves represented by figures 1, la, and Ic, showing 
 the visceral area with its muscle scars, and an unusually complex system of vascular canals. U. S. 
 Nat. Mus. Cat. No. 17440d. Specimen figured by Walcott [1887, PI. I, fig. 1.5a: and 18^a, PI. 
 LXVII, fig. 4a]. 
 
 Obolus lamborni (Meek) (p. 393). 
 
 Figure 2. Interior of a flattened ventral valve from Locality llj. Middle Cambrian shale at Mine Lamotte, Madison 
 
 County, Missouri. V. S. Nat. Mus. Cat. No. 51553a. 
 2a. Cast of the interior of a ventral valve associated with the valve represented by figure 2. L"^. S. Nat. Mus. 
 
 Cat. No. 51553b. 
 2b. Very fine cast of the interior of a ventral valve from Locality 121, Middle Cambrian Rogersville shale, road 
 
 just east of Harlan Knob, 4 miles northeast of Rogersville, Hawkins County, Tennessee. U. S. 
 
 Nat. Mus. Cat. No. 51558a. 
 2c. Cast of the interior of a ventral valve associated with the specimen represented by figure 2b, which has 
 
 very much the same appearance as the specimen represented by figure 2a from the shale in Missouri. 
 
 U. S. Nat. Mus. Cat. No. 51558b. 
 2d. Cast of the outer surface of a ventral valve associated with the valves represented by figures 2b and 2c, 
 
 showing the strong concentric stride and fine radiating striie. V. S. Nat. Mus. Cat. No. 515.58c. 
 2e and 2f. Casts of the interior of compressed ventral valves associated with those represented by figures 
 
 2b-d, illustrating variation in form, figure 2f being the result of distortion. -U. S. Nat. Mus. Cat. 
 
 Nos. 51558d and 51558e, respectively. 
 2g and 2h. Very fine interior casts of dorsal valves associated with the ventral valves illustrated by figures 
 
 2b-f. The variation in the character of the inner surface is well illustrated by the.'»e two figures; in 
 
 figure 2h there are only faint indications of papilke, while in figure 2g they are abundant. U. S. 
 
 Nat. Mus. Cat. Nos. 51558f and 51558g, respectively. The area of figure 2h is represented in figure 2m. 
 2i and 2j. Casts of the interior of two dorsal valves associated with the two ventral valves represented by 
 
 figures 2 and 2a, at Locality llj, near Mine Lamotte, Missouri. U. S. Nat. Mus. Cat. Nos. 51553c 
 
 and 51553d, respectively. Figure 2j represents the type specimen. 
 2k. Cast of a dorsal valve associated with the valves represented by figures 2b-h (Locality 121 1, tliat illustrates 
 
 variation in form. U. S. Nat. Mus. Cat. No. 51558h. 
 21. Cast of largo dorsal valve from Locality 124a, Middle Cambrian shales on Big Creek, southeast of Harlan 
 
 Knob, 4 miles northeast of Rogersville, Hawkins County, Tennessee. I'. S. Nat. Mus. Cat. No. 
 
 51557a. 
 2m. Enlargement and partial restoration of the area of the dorsal valve represented by figure 2h. I'. S. Nat. 
 
 Mus. Cat. No. 51558g. 
 2n. Cast of a dorsal valve associated with the valves represented by figures 2b-h. U. S. Nat. Mus. Cat. No. 
 
 51.558i. 
 80 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XXII 
 
 2" 
 
 FRANCES WIESER DEL. 
 
 .iELlOTVPC CO BOSTrtll 
 
PLATE XXIII. 
 
 62667°— VOL 51, pt 2—12 6 81 
 
PLATE XXIII. 
 
 a. Central lateral space at area, 
 a'. Outer lat<!ral space of area. 
 f. Flexure lines of area, 
 h. Central muscle scar, 
 i. Transinedian muscle scar. 
 
 j. Anterior lateral muscle scar, 
 p. Pedicle ktoovc. 
 s. Median septum. 
 V. Visceral cavity, 
 vs. Main vascular sinus. 
 
 Obolus willisi (Walcott) (p. 420). 
 
 Figure 1. Cast of a ventral valve, the type specimen, compressed in shale, Locality 140a, .Mi<lille CamVjrian, near 
 
 Cave Spring, Floyd County, Georgia. U. S. Nat. Mus. Cat. No. 27.345a. 
 la. Cast of a ventral valve compressed in shale, Locality 107b, Middle Cambrian, near Copiier Ridge, 11 miles 
 
 northwest pf Knoxville, Tennessee. U. S. Nat. Mus. Cat. No. 27343a. 
 lb. Cast of a ventral valve compressed in shale, that shows the pitted or punctate character of the interior of the 
 
 shell. Same locality as specimen represented by figure la. U. S. Nat. Mus. Cat. No. 27343b. 
 Ic. Cast of the outer surface of a ventral valve, from same band of shale as specimen represented by figure la. 
 
 U. S. Nat. Mus. Cat. No. 27343c. 
 Id. Cast of the outer surface of a dorsal valve associated with specimen represented by figure la. U. S. Nat. 
 
 Mus. Cat. No. 27343d. 
 le. Cast of a ventral valve distorted by compression in the same band of shale as the specimen represented by 
 
 figure la. U. S. Nat. Mus. Cat. No. 27343e. 
 If. Cast showing part of a ventral valve, the outline of which is restored from associated specimens. It occurs 
 
 in the calcareous sandstone embedded in the shales of Locality 107b, Middle Cambrian, near Copper 
 
 Ridge, 11 miles northwest of Knoxville, Tennessee. U. S. Nat. Mus. Cat. No. 27343f. 
 Ig. Cast of the interior of a dorsal valve associated with the specimen represented by figure If. V. S. Nat. 
 
 Mus. Cat. No. 27343g. 
 Ih. Cast of the interior of a dorsal valve a.ssociated with specimen represented by figure If but which is more 
 
 transverse. U. S. Nat. Mus. Cat. No. 27343h. 
 li. Distorted cast of a ventral valve from Locality 101b, Middle Cambrian shale 3.5 miles southwest of Rogers- 
 
 ville, Tennessee. U. S. Nat. Mus. Cat. No. 27344a. 
 Ij. Flattened ventral valve, showing the strong interrupted radiating lines and the strong concentric rugose 
 
 lines of growth. Locality 93, Upper Cambrian shale, near Jordans on (.'owan Creek, Cherokee County, 
 
 Alabama. IT. S. Nat. Mus. Cat. No. 27346a. 
 
 LiNGULELLA TAEPA (Walcott) (p. 584). 
 
 Figure 2. Exfoliated ventral valve from sandy shales, which shows general outline and some of the markings of the 
 
 interior of the shell. U. S. Nat. Mus. Cat. No. 27342a. 
 2a. Compressed, slightly distorted ventral valve, the type specimen, from argillaceous shales interbedded 
 
 with the sandy shales in which "the specimen represented by figure 2 occurs. V. S. Nat. Mus. Cat. 
 
 No. 27342b. 
 2b. Cast of a dorsal valve, from calcareous layers in the sandy shale in which specimen represented by figure 2 
 
 occurs. U. S. Nat. Mus. Cat. No. 27342c. 
 2c. Somewhat more elongate shell than that represented by figure 2b, with which it is associated, and which 
 
 is somewhat doubtfully identified as a dorsal valve. U. S. Nat. Mus. Cat. No. 27342d. 
 
 The specimens represented are all from Locality 11, Middle Cambrian, 1 mile east of Post Oak Springs, Roane 
 County, Tennessee. 
 
 Obolus mcconnelli (Walcott) (p. .396). 
 
 Figure 3. Interior of a crushed and broken ventral valve, the type specimen, from Locality 14s, Middle Cambrian 
 Ogygopsis zone on Mount Stephen, British Columbia. U. S. Nat. Mus. Cat. No. 51572a. 
 3a. Interior of an associated fragmentary ventral valve of the broad form. U. S. Nat. Mus. Cat. No. 51572b. 
 Copied from Walcott [1908c, PI. I, fig. 2]. (See note under fig. 3d, below.) 
 
 Obolus mcconnelli pelias (Walcott) (p. 398). 
 
 (PI. XXXIX, figs. 5, 5a-c.l 
 
 Figure 3b. Interior of a broad form of dor,«al valve, the type specimen, from Locality llq, Mi(l<lle Cambrian Marjuni 
 limestone, ridge east of Wheeler Amphitheater, House Range, L'tah. U. S. Nat. Mus. Cat. No. 51592a. 
 3c. Interior of an associated dorsal valve. U. S. Nat. Mus. Cat. No. 51592b. 
 82 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH Lt PL. XXIII 
 
 FRANCES WIESER DEL. 
 
 MELIOTTPE CO BOSTOM 
 
PLATE XXIII. 83 
 
 Obolus septalis (Walcott) (p. 414). 
 
 [PI. XXXIV, n«.s. 2, 2a.l 
 
 Figure 3d. Dorsal valve from Locality 14s, Middle Cambrian Ogygopsis zone on Mount Stephen, British Columbia. 
 U. S. Nat. Mus. Cat. No. 24069a. Copied from Walcott [lOOSc, V\. I, fit;. 2a], where it was figured 
 as Obolus mcconnelli. 
 
 Obolus mcconnelli decipiens Walcott (p. 398). 
 
 Figure 4. Compressed ventral valve, the type specimen, from Locality 7v, Upper Cambrian shales 4.25 miles south- 
 southeast of Emigrant Peak, Esmeralda County, Nevada. U. S. Nat. Mus. Cat. No. 51.586a. 
 
 4a. Compressed ventral valve from Locality 8m, Middle Cambrian limestone 4 miles northeast of Osceola, 
 White Pine County, Nevada. U. S. Nat. Mus. Cat. No. 51585a. 
 
 4b. Ventral valve associated with specimen represented by figure 4a. U. S. Nat. Mus. Cat. No. 51585b. 
 
 Obolus fragilis (Walcott) (p. 392). 
 
 Figure 5. Cast of the interior of a ventral valve, the type specimen, from Locality 1, Middle Cambrian shales on 
 
 Manuels Brook, Conception Bay, Newfoundland. U. S. Nat. Mus. Cat. No. 27317a. 
 5a. Dorsal valve associated with the specimen represented by figure 2. U. S. Nat. Mus. Cat. No. 27317b. 
 5b. Outline of the dorsal valve, showing area, from Locality 2, Middle ('ambrian .shale from a higher horizon 
 
 than that represented by figure 5, on Manuels Brook, Conception Bay, Newfoundland. U. S. Nat. 
 
 Mus. Cat. No. 569na. 
 5c. Cast of the interior of a dorsal valve associated with the specimen represented by figure 5. U. S. Nat. 
 
 Mus. Cat. No. 27317c. 
 5d. Cast of the interior of a dorsal valve, showing concentric and radiating stri*, as.sociated with specimen 
 
 represented by figure 5b. U. S. Nat. Mus. Cat. No. 56911b. 
 5e. Broad dorsal valve associated with specimen represented by figure 5. U. S. Nat. Mus. Cat. No. 27317d. 
 
PLATE XXIV. 
 
 85 
 
PLATE XXIV. 
 
 a. Central lateral space of area. p. Pedicle groove, 
 
 a'. Outer lateral space of area. , s. Median septum, 
 
 f. Flexure line of area. v. \Tsceral cavity, 
 
 h. Central muscle scar. vs. Main vascular sinus, 
 j. Anterior lateral muscle scar. 
 
 LiNGULELLA NANNO (Willcott) (p. 521). 
 
 Figures 1 and la. Ventral valves, preserving natural form and convexity, from Locality 16, Middle Cambrian 
 limestones in Blountsville Valley, Blount County, Alabama. U. S. Nat. Mus. Cat. Nos. 27328a and 
 27328b, respectively. Figure la represents the type specimen, 
 lb and Ic. Dorsal valves associated with the specimens represented by figures 1 and la. U. S. Nat. Mus. 
 
 Cat. Nos. 27328c and 27328d, respectively. 
 Id. Unusually large and convex dorsal valve from Locality 91, Middle Cambrian limestone at Cedar 
 Bluff, Cherokee County, Alabama. U. S. Nat. Mus. Cat. No. 57005a. 
 
 LiNGULELLA LEGS (WalcOtt) (p. 513). 
 
 Figure 2. Partly exfoliated ventral valve. U. S. Nat. Mus. Cat. No. 27323a. 
 
 2a. Cast of the interior of a ventral valve, the type specimen. U. S. Nat. Mus. Cat. No. 27323b. 
 2b and 2c. Casts of interior of two dorsal valves. 2c is strongly convex and unusually narrow and elongate. 
 T'. S. Nat. Mus. Cat. Nos. 27323c and 27323d, respectively. 
 
 The specimens represented are all from Locality 96, Upper Cambrian limestone, 1.5 miles south of Rome, Floyd 
 County, Georgia. 
 
 LiNGULELLA HELENA (Walcott) (p. 506). 
 
 Figure 3. Exterior of a slightly distorted ventral valve from Locality 302s, Middle Cambrian siliceous shale 1.5 miles 
 
 south of Helena, Lewis and Clark County, Montana. U. S. Nat. Mus. Cat. No. 27320a. 
 3a and 3b. Casts in siliceous shale of the interior of two ventral valves that differ in outline, from the locality 
 
 represented by figure 3. V. S. Nat. Mus. Cat. Nos. 27320b and 27320c, respectively. Figure 3a 
 
 represents the type specimen. 
 3c. Cast of the interior of a.dorsal valve showing area, from the locality represented by figure 3. U. S. Nat. 
 
 Mus. Cat. No. 27320d. 
 3d. Small ventral valve doubtfully referred to the species, from Locality 30a, Middle Cambrian shale in 
 
 Big Cottonwood Canyon, near Salt Lake City, Utah. U. S. Nat. Mus. Cat. No. 51819a. 
 
 LiNGULELLA DUBIA (Walcott) (p. 494). 
 
 Figure 4. Cast of interior of ventral valve, the type specimen, associated with Obolus (Westonia) ella at Locality 31, 
 Middle Cambrian shales at Pioche, Nevada. V. S. Nat. Mus. Cat. No. 27314a. 
 4a. Cast of interior of dorsal valve on same piece of shale with the specimen represented by figure 4. U. S. 
 Nat. Mus. Cat. No. 27314b. 
 
 LiNGULELLA ARGITA (Walcott) (p. 478). 
 
 Figure 5. Perfect ventral valve, the type, from Lmality 3131, Upper Cambrian limestone at Schellbourne, Schell 
 Creek Range, Nevada. U. S. Nat. Mu.-s. Cat. No. 27305a. DrawTi from specimen represented by 
 White [1877, PI. Ill, fig. 2a] as LinguUi f maiiliada. 
 5a. Dorsal valve that is doubtfully referred Ifi this species from Locality 313a, Mi<ldle Cambrian limestone 
 
 at Schellbourne, Nevada. U. S. Nat. Mus. Cat. No. 51845a. 
 5b. Partly exfoliated dorsal valve from Locality lOy, Middle Cambrian Marjum iimeatone, near Marjum 
 Paas, House Range, Utah. U. S. Nat. Mus. Cat. No. 58303. 
 86 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XXIV 
 
 FRANCES VvieSER DEL. 
 
 LiOTvpe CO eosTOH 
 
PLATE XXIV. 87 
 
 LiNGULELLA AUGA (Walcott) (p. 480). 
 
 FiouREs 6 and 6a. Casts in shaly limcstune (if interior of two ventral valves. U. S. Nat. Mu.s. Cat. Nos. 27306a and 
 
 27306b, respectively. 
 6b. Cast of the posterior portion of the interior of a distorted ventral valve, the type specimeri. U. S. Nat. 
 
 Mus. Cat. No. 27306c. 
 6c. Cast of the posterior portion of the interior of a ventral valve, showing a trace of the vi.sceral area. U. S. 
 
 Nat. Mus. Cat. No. 27306d. 
 6d and 6e. Casts of the interior of two dorsal valves. U. S. Nat. Mus. Cat. Nos. 27306e and 27306f 
 
 respectively. 
 
 The specimens illustrated by figures 6, 6a-e are from Locality 10a, Middle Cambrian shaly sandstones at Shooka 
 Gap, 10 miles southeast of Knoxville, Tennessee. 
 
 Figures 6f and 6g. Ventral and dorsal valves from Locality 10b, a siliceous limestone interbedded in the Middle 
 Cambrian shaly sandstones at Shocks Gap, 10 miles southeast of Knoxville, Tennessee. The outer 
 surface with strong concentric stria? is finely preserved. U. S. Nat. Mus. Cat. Nos. 27306g and 27306h, 
 respectively, 
 
 LiNGULELLA TUMiDA Mattliew (p. 537). 
 
 Figure 7. Exterior of ventral valve from Locality 13i, Middle Cambrian sandy shales on Ciillis Brook, Cape Breton, 
 
 Nova Scotia. U. S. Nat. Mus. Cat. No. 51769a. 
 7a. Cast of the interior of a ventral valve associated with the shell represented by figure 7, showing the high 
 
 area and strong vascular sinuses. U. S. Nat. Mus. Cat. No. 51769b. 
 7b. Cast of the interior of a ventral valve from Locality 13r, a little different horizon from that represented 
 
 by Locality 131, Middle Cambrian sandy shales on Gillis Brook, Cape Breton, Nova Scotia. U. S. 
 
 Nat. Mus. Cat. No. 57011a. 
 7c. Exterior of ventral valve a,ssociatcd with the shell represented by figure 7. U. S. Nat. Mus. Cat. No. 
 
 51769c. 
 7d. Cast of the interior of a ventral valve associated with the shell represented by figure 7b, retaining a 
 
 portion of the shell on the umbo. U. S. Nat. Mus. Cat. No. 57011b. 
 
PLATE XXV. 
 
 89 
 
PLATE XXV. 
 
 a. Central lateral space of are<i. p. Pedicle ktootc. 
 
 a'. Outer lateral space of area. ps. Parietal l)aad. 
 f. Flexure line of area. s. Median septum, 
 
 h. Central muscle scar. v. Visceral cavity, 
 
 i. Transmedian mu.scle scar. vs. Main vascular sinus, 
 j. .\nterior lateral muscle scar. 
 
 LiXGULELLA IIAYESI (Walcott) (p. 505). 
 
 Figure 1. Cast of the interior of a ventral valve, showing the area and portions of the visceral cavity. I'. S. Xat. 
 
 Mus. Cat. No. 27319] . 
 la. Interior of a partly weathered ventral valve. U. S. Nat. Mus. Cat. No. 27319a. 
 lb and Ic. Casts of the interior of the ventral valve, showing the position of the main vascular sinuses, the 
 
 visceral cavity, and the area. U. S. Nat. Mus. Cat. Nos. 27310b and 27319c, respectively. Figure 
 
 lb represents the type specimen. 
 Id. Enlargement of the cast of the area i>f the ventral valve, showing the pedicle groove, the flexure line, and 
 
 the central and outer lateral spaces of the area. U. S. Nat. Mus. Cat. No. 27319d. 
 le. Cast of the interior of a dorsal valve showing the position of the central (h) and anterior lateral (j) muscle 
 
 scars, the scar of the parietal band (ps), also the arching forward of the center of the area. U. S. Nat. 
 
 Mus. Cat. No. 27319e. 
 If, Ig, Ih, and li. Casts of the interior of dorsal valves, showing variation in form of the valve and in the posi- 
 tion of the parietal band and main vascular sinus. The latter is especially well shown by figure Ig. 
 
 U. S. Nat. Mus. Cat. Nos. 27319f, 27319g, 27319h, and 273191, respectively. 
 Ij. Enlargement of the area of the dorsal valve represented by figure If. U. S. Nat. Mus. Cat. No. 27319f. 
 
 All of the specimens represented occur on the exterior of siliceous nodules, or on breaks across them, from Locality 
 90x, Middle Cambrian Conasauga shale, Coosa Valley, Cherokee County, Alabama. 
 
 Obolus (Westoxia) chuarensis (Wiilcott) (p. 454). 
 
 Figures 2 and 2a. Partly exfoliated ventral valves from Locality 73a, Middle Cambrian sandstone, Chuar Valley, 
 
 Grand Canyon of the Colorado, Arizona, showing some variation in form. V. S. Nat. Mus. Cat. Nos. 
 
 57020a and 57020b, respectively. Figure 2 represents the type specimen. 
 2b. Crushed ventral valve from Locality 74b, Middle Cambrian sandstone in Nunkoweap Valley, Grand 
 
 Canyon of the Colorado, Arizona. U. S. Nat. Mus. Cat. No. 57021a. 
 2c. Exterior of a rather large dorsal valve from Locality 74, Middle Cambrian sandstone at the head of Nimko- 
 
 weap Valley, Grand Canyon of the Colorado, Arizona. V. S. Nat. Mus. Cat, No. 27310a. 
 2d. Cast of part of the interior of a dorsal valve associated with the shells represented by figures 2 and 2a, 
 
 showing a median depression and the area. V. S. Nat. Mus. Cat. No. 57020r. 
 2e. Strongly marked cast of the interior of a dorsal valve associated with the shell represented by figure 2c, 
 
 showing the depression filled by the ridges adjacent to the main vascular sinuses, a strong central 
 
 groove corresponding to the median septum, and the central muscle scars (h). U. S. Nat. Mus. 
 
 Cat. No. 27310b. 
 
 Obolu.s zExrs (Walcott) (p. 4_'l). 
 
 Figures 3, 3a, and 3b. Partly exfoliated ventral valves, showing the external form and something of the character 
 of the different layers forming the shell. V. S. Nat. Mus. Cat. Nos. 27347a, 27347b, and 27347c, 
 respectively. Figure 3a represents the type specimen. 
 3c. Partly exfoliated dorsal valve. V. S. Nat. Mus. Cat. No. 27347d. 
 
 The specimens represented are all fmni Locality 74, Middle Cambrian sandstone, near the head of Nunkoweap 
 Valley, Grand Canyon of the Colorado, .Vrizona. 
 
 Obolus lamborni minimus (Walcott) (p. 395). 
 
 Figures 4 and 4a. Casts of ventral valves that were comprc.«.sed in the shale, l'. S. Nat. Mus. Cat. Nos. 27322a and 
 27322b, respectively. Figure 4 represents the type specimen. , 
 
 4b. Dorsal valve associated with the ventral valves represented by figures 4 and 4a. U. S. Nat. Mus. Cat. 
 No. 27322c. 
 
 The specimens illustrated are all from Locality 101a. Middle Cambrian Rogersville shale, 3.5 miles southwest of 
 Rogersville, Ilawkiivs County, Tennessee. 
 90 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XXV 
 
 t) 
 
 2b 
 
 ?" 
 
 FRANCES WIESER DEL. 
 
 cLiOTVPE CO e=si 
 
PLATE XXVI. 
 
 91 
 
PLATE XXVI. 
 
 c. Trapezoidal area, including central, middle 
 lateral, and outside lateral muscle scars. 
 
 f. Fle.xure line of area. 
 
 g. Umbonal muscle scar. 
 h. Central muscle scar. 
 
 1. Transmedian muscle scar. 
 
 j. Anterior lateral muscle scar, 
 m. Pedicle muscle, 
 p. Pedicle groove, 
 s. Median septum. 
 V. Visceral cavity, 
 vs. Main vascular sinus. 
 
 LiNGULELLA PHAON (Walcott) (p. 525). 
 
 Figure 1. A'entral valve from Locality 84a, Upper Cambrian sandstone at River Junction, Houston County, Minne- 
 sota, the exterior of which has been slightly injured by abrasion. U. S. Nat. Mus. Cat. Xo. 27406a. 
 
 la. Dorsal valve associated with the specimen represented by figure 1. U. S. Nat. Mus. Cat. No. 27406b. 
 
 lb. Strongly marked cast of the interior of a ^•entral valve from Locality 98x, L^pper Cambrian sandstone near 
 Eau Claire, Wisconsin. This specimen shows the broken edge of the undercut that extended back 
 under the area and the deeply impressed character of t,he channels of the main vascular sinuses; also 
 the large size of the pits or punctae on the interior of the .shell. U. S. Xat. Mus. Cat. Xo. 27331a. 
 
 Ic. Cast of the interior of a ventral valve, the type specimen, associated with the specimen represented by fig- 
 ure lb, showing more definitely the interior features of the shell. The divided umbonal muscle scars 
 and the pedicle muscle scar are drawn from an associated ventral valve. The central, middle lateral, 
 and outside lateral muscle scars are not differentiated in the deeply impressed trapezoidal area (c); 
 the anterior lateral muscle sears (j) are well shown. U. S. Xat. Mus. Cat. Xo. 27331b. 
 
 Id. Interior cast of a dorsal valve associated with the specimen represented by figure lb, having the same 
 strongly marked characteristics as the casts of the ventral valve. The cast of the central ridge is very 
 pronounced, and it is ditHcult to say just where the central muscle scars (h) were located. They 
 appear to be, however, as indicated on the ilra^ving, which brings them very close to the small 
 anterior lateral scars. U. S. Nat. Mus. Cat. No. 27331c. 
 
 le. Interior cast of a very strongly marked dorsal valve associated with the specimen represented by figure 
 lb, in which the detailed characters are lost. The general effect of this cast is much like that of 
 the interior cast of the dorsal valve of Lirigulella grandis (PL XXXVIII, fig. 2d). U. S. Nat. Mus. 
 Cat. Xo. 27331d. 
 
 Obolus sixoe (Walcott) (p. 415). 
 
 Figure 2. Interior cast of a veritral valve. U. S. Xat. Mus. Cat. Xo. 27341a. 
 
 2a. Interior of a ventral valve preserving the area and showing the undercut beneath the area. The impres- 
 sions of the visceral cavity are indistinct. U; S. Nat. Mus. Cat. Xo. 27341b. Another specimen 
 (Cat. Xo. 27341c) was used to restore parts of the drawing. 
 
 2b.. Cast of the interior of a ventral valve, showing a portion of the shell and the posterior ])ortion of the main 
 vascular sinuses. L'. S. Nat. Mus. Cat. Xo. 27341d. 
 
 2c. Dorsal valve from which the exterior layer has been removed so as to .show the edges of the oblique interior 
 lamellae. U. S. Xat. Mus. Cat. No. 27341e. 
 
 2d. Cast showing part of the interior of a ventral valve. U. S. Xat. Mus. Cat. Xo. 27.341f. 
 
 The specimens represented by figures 2, 2a-d are from Locality 68y, L'pper Cambrian reddish brown sandstone on 
 Packsaddle Mountain, Llano County, Texas. 
 
 Figure 2e. Cast of an interior of a ventral valve. The strongly marked channel of the parietal scar and the elevated 
 ridge in front of it is very characteristic of Obolus apollinis (PL VII). The posterior portion toward 
 the area is restored from a second specimen. U. S. Nat. Mus. Cat. No. 51627a. 
 
 2f. Cast showing part of the interior of a dorsal valve, the type specimen. The anterior lateral .scars are well 
 shown on another specimen. U. S. Nat. Mus. Cat. X"o. 51627b. 
 
 2g. An elongate dorsal valve preserving the outer surface of the shell. V. S. Nat. Mus. Cat. No. 51627c. 
 
 2h. Enlai^ement of the anterior portion of a .shell to illustrate tlie obli(|ue lamcllie forming the strong shell. 
 IT. S. Nat. Mus. Cat. No. 5I627.1. 
 
 The specimens represented by figures 2e-h are from Locality 70, L'pper Cambrian limestone near Morgans Creek, 
 Burnet County, Texas. 
 92 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XXVI 
 
 FRANCES WIESER DEL. 
 
 HELIOTyfe CO BOSTON 
 
PLATE XXVI. 93 
 
 LiNGULELLA FKANKLINENSIS (Walcott) (p. 501). 
 
 Figure 3. Somewhat crushed ventral valve, the type, from which most nf the shell has been exfoliated. Locality 87, 
 Lower Cambrian limestone near Ilighgate Falls, Franklin County, Vermont. U. S. Nat. Mus. Cat. 
 No. 27318a. 
 
 3a. Dorsal (?) valve from the locality represented by figure 3, preserving the outer surface. This may be. how- 
 ever, a distorted ventral valve. U. S. Nat. Mus. Cat. No. 27318b. 
 
 3b. Largest ventral valve in the collection. Locality 28a, Middle ? Cambrian, near Parker's quarry, Georgia, 
 Vermont. U. S. Nat. Mus. Cat. No. 52454a. 
 
 LiNGULELLA INO (Walcott) (j). 507). 
 
 Figure 4. Cast of the interior of a ventral valve, the type specimen, showing somewhat imperfectly the \-isceral 
 
 cavity and main vascular sinuses. U. S. Nat. Mus. Cat. No. 27321a. 
 4a. Ventral valve preserving a portion of the shell, showing the area, pedicle groove, and flexure lines very' 
 
 clearly. U. S. Nat^ Mus. Cat. No. 27321b. 
 4b. Cast of the interior of a dorsal valve, showing a relatively large area and portions of the shell adhering to the 
 
 cast. U. S. Nat. Mus. Cat. No. 27321c. 
 
 The specimens represented are all from Locality 13b, Middle Cambrian sandstones northeast of Rhea Springs, 
 Roane County, Tennessee. 
 
PLATE XXVII. 
 
 95 
 
PLATE XXVII. 
 
 c. Trapezoidal area, IncliKiinK central, middle J. \nterior lateral muscle scar. 
 
 lateral, and outside lateral muscle scars. m. Pedicle muscle. 
 
 g. Umlional muscle scar. v. Visceral cavity, 
 
 h. Central muscle sear. vs. Main vascular sinus. 
 
 LiNGULELLA PRIMA (Conrad MS.) (Hall) (p. 526). 
 
 FiGt'RE 1. Cast of the interior of a ventral valve, .showing the pestle-shaped ridge that filled the median groove of the 
 interior of the shell. U. S. Xat. Mils. Cat. No. 27435a. 
 la. Exterior of a ventral valve, showing rather strong undulations of growth. U. S. Xat. Mus. Cat. No. 2743.5 
 lb. Fragment of a ventral valve, showing the cast of the area, the di\ided umlicnial muscle scar (g), and the 
 
 pedicle scar (m). U. S. Nat. Mus. Cat. No. 27435c. 
 Ic. Partly exfoliated dorsal valve. U. S. Nat. Mus. Cat. No. 27435(1. 
 
 The specimens represented are all from Locality 77, I'pper Cambrian sandstone, Ausable Chasm, Essex County, 
 New York. 
 
 LiNGXJLELLA IRIS (Billings) (p. 509). 
 
 Figure 2. Dorsal valve, the type specimen, from Locality 319d, L'pper Cambrian, Point Levis, Quebec, Canada. 
 Geol. Survey Canada. Redrawn from the specimen described and figured by Billings [lS65a, p. 301, 
 fig. 290] as Lingula iris. 
 
 Obolus prindlei (Walcott) (p. 409). 
 
 Figure 3. Ventral valve, the type, from Locality 72a, Lower Cambrian. 1 mile southwest of W'ynantskill, Rensselaer 
 County, New York, showing the character of the outer surface and also of the surface of the inner 
 layers where the shell Ls exfoliated over its umbonal portion. U. S. Nat. Mus. Cat. No. 27333a. 
 
 3a. Cast of the interior of a ventral valve which is broken away a little at the beak. This specimen Ls associated 
 on the same hand specimen with the valve represented in figure 3. V. S. Nat. Mus. Cat. No. 27333b. 
 
 3b. Portionof a ventral valve from Locality 72a, Lower Cambrian, 1 mile southwest of Wynantskill, Rensselaer 
 County, New York, showing the cast of the finely punctate inner surface and the peculiar lamellose- 
 like striae of growth upon the area. U. S. Nat. Mus. Cat. No. 27333c. 
 
 3c. Cast of the interior of a dorsal valve, associated on the same hand specimen with the \alve represented by 
 figure 3, showing the area. U. S. Nat. Mus. Cat. No. 27333d. 
 
 3d. Exterior of a dorsal valve from Locality 72, Lower Cambrian limestone 5 miles west of Albany, ReiLsselaer 
 County, New York, illustrating the character of the outer surface. U. S. Nat. Mus. Cat. No. 27334a. 
 
 3e. Cast of the interior of a dorsal valve that is more conve.x and more oval in outline than the specimen repre- 
 sented by figure 3, which is associated on the same hand specimen with it. U. S. Nat. Mus. Cat. 
 No. 27333e. 
 
 Obolus ctane (Billings) (p. 3SS). 
 
 Figure 4. Cast of the interior oi a ventral valve, the type specimen, which preserves a portion of the inner layers 
 
 of the shell over the visceral area. 
 4a. Imperfect cast of a ventral valve, showing the lamellated shell structure. 
 4b. Cast of the interior of a dorsal valve. The muscle scars are obscured in the specimen from which the figure 
 
 has been drawn, and those that appear in the figure are from another specimen occurring in the same 
 
 fragment of limestone. 
 
 The specimens represented are all from Locality 314d, Lower Ordovician limestone 4 miles northeast of Portland 
 Creek, Newfoundland, and are now in the collections of the Geological Survey of Canada. These specimens were 
 illustrated by Billings [18G5a, figs. 20a-d, p. 215], but further identification of his figures with those in this monograph 
 Ls impossible. 
 
 LiNGULELLA lOLE (Billillgs) (p. 50S). 
 
 Figures Sand 5a. Ventral and dorsal valves, respectively, from Locality 314d, Lower Ordovician limestone 4 miles 
 • northeast of Portland (reek, Newfoundland. Geol. Survey Canada. Redrawn from the two speci- 
 mens figured by Billings [ISGoa, figs. 199a-e, p. 215] as Lingula iolc. The ventral may be taken as 
 the type. 
 96 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XXVII 
 
 3' 
 
 3" 
 
 •') 
 
 
 FRANCES WIE8ER DEL. 
 
 MCLioTvpE cc eo3roN 
 
PLATE XXVII. 97 
 
 LiNGTXLELLA IRENE (Billings) (p. 50S). 
 
 Figure 6. Interior of a flattened ventral valve, preserving the area and portions of the shell. The confenlric striatum 
 of the exterior of the shell is shown at the place where the shell is broken away. 
 6a. Partly exfoliated outer surface of a dorsal valve that is compressed in the shale. 
 
 The specimens represented are both from Locality 315a, Lower Ordovician Levis shale at Point Levis, Quebec, 
 Canada, and are in the collection of the Geological Survey of Canada. They were described and fiirured by I'illings 
 [18C2d, pp. 71-72, figs. 64a-b] as Lingula irene. Figure 6 may be take:i as the type. 
 
 LiNGTJLELLA CUNEOLA (Whitfield) (p. 4SS). 
 
 FiGiRE 7. Cast of a ventral valve from Locality 355, Middle Cambrian sandstone. Red Canyon Creek, Black Hills, 
 
 South Dakota. U. S. Nat. Mas. Cat. No 24587a. Type specimen, figured by Whitfield [1S80, PL I, 
 
 fig. 6] as Lingulepis cuneolus. The specimen figured by Whitfield [1880, PI. I, fig. 5] is not figured in 
 
 this monograph. 
 
 7a. Cast of the interior of a ventral (?) valve, associated with the valve represented by figure 7, preserving a 
 
 portion of the shell on the outer margins. V. S. Nat. Mus. Cat. No. 33S73a. 
 7b. Cast of the interior of a dorsal valve, asseciated with specimens represented by figures 7 and 7a. V. S. 
 Nat. Mus. Cat. No. 33873b. 
 62667°— VOL 51, pt 2—12 7 
 
PLATE XXVIII. 
 
 99 
 
PLATE XXVIII. 
 
 a. Cfintral lateral space of area. p. Pedicle groove. 
 a'. Outer lateral sjiace of area. s. Median-septum. 
 
 f. Flexure line of area. V. Visceral cavity. 
 
 h. Central muscle scar. vs. Main vascular sinus. 
 i. TranS7nedian muscle scar. y. See text (p. 478). 
 
 j. -Vnterior lateral muscle scar. 
 
 LiNGULELLA AMPLA (OwCIl) (p. 477). 
 
 Figure 1. Ventral valve partly broken away near the apex, from Locality 339e, Middle Cambrian sandstone on 
 Mountain Island, Minnesota. U. S. Nat. Mus. Cat. No. 17S59b. Type specimen, figured by Owen 
 [1852, PI. IB, fig. 5] as Lingula ampla. The specimen represented by figure 12 of the same plate 
 (Catalogue No. 17859a) is not figured in this monograph. 
 
 la. Ventral valve, from Locality 84s, Middle Cambrian sandstone near Dakota, Winona County, Minnesota. 
 U. S. Nat. Mus. Cat. No. 35241a. 
 
 lb. Dorsal valve, associated with specimen represented by figure la. L'. S. Nat. Mus. Cat. No. 35241b. 
 
 Ic. Cast of the interior of a ventral valve associated with the specimen represented by figure la. U. S. Nat. 
 Mus. Cat. No. 35241c. 
 
 Id. Cast of the interior of the ventral valve represented in figure If, enlarged. Locality 84s, Middle Cambrian 
 sandstone near Dakota, Winona County, Minnesota. U. S. Nat. Mus. Cat. No. 35241d. 
 
 le. Cast of the interior of the posterior portion of a ventral valve associated with the specimen represented by 
 figure la. U. S. Nat. Mus. Cat. No. 3.5241e. 
 
 If. Cast of the interior of a ventral valve showing an unusual feature at y. This sijccimen is enlarged in 
 figure Id. U. S. Nat. Mus. Cat. No. 35241d. 
 
 Ig. Cast of the interior of a dorsal valve associated with the specimen represented by figure la. U. S. Nat. 
 Mus. Cat. No. 3o241f. 
 
 Ih. Cast of the interior of a dorsal valve associated with the specimen represented by figure la. L^. S. Nai. 
 Mus. Cat. No. 35241g. 
 
 li. Enlargement of the area shown in figure Ih. L'. S. Nat. Mus. Cat. No. 35241g. 
 
 Ij. Ventral valve tentatively referred to this species, from Locality 88a, Middle Cambrian limestone at Dead- 
 wood, Black Hills, South Dakota. U.S. Nat. Mus. Cat. No. 51784a. 
 
 Obolus (Westonia) stoneanus (Wliitfield) (p. 465). 
 
 [I'l. XLIX.figs. 2and2a.l 
 
 Figure 2. Cast of the interior of a compressed ventral valve. LT. S. Nat. Mus. Cat. No. 51727a. 
 
 2a. Cast of the interior of a ventral valve, showing a few traces of the interior markings of the shell, t'. S. 
 
 Nat. Mus. Cat. No, 51727b. 
 2b. Enlargement of a cast of the area of a ventral valve. U. S. Nat. Mus. Cat. No. 51727c. 
 2c. Cast of the posterior portion of the interior of a ventral valve. U. S. Nat. Mus. Cat. No. 51727d. 
 2d. Enlargement of a portion of the outer surface of a ventral valve. U. S. Nat. Mus. Cat. No. 51727e. 
 2e. Cast of the interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 51727f. 
 2f. Posterior half of a cast of the interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 51727g. 
 2g. Cast of the outer surface of a dorsal valve. V. S. Nat. Mus. Cat. No. 51727h. 
 
 The specimens represented are all from Locality 85s, Ujjper Cambrian sandstone at Prairie du Sac, Sauk County, 
 Wisconsin. 
 
 100 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XXVIII 
 
 FRANCES WIESER DEL. 
 
 LIOTVPE CO BOSTON 
 
PLATE XXIX. 
 
 101 
 
PLATE XXIX. 
 
 h. Central muscle sear. s. Median septum, 
 
 i. TraiisirieJian muscle scar. v. Visceral cavity.- 
 
 j. Anterior lateral muscle scar. vs. Main vascular sinus. 
 
 LiNGULELLA FEKRUGiNEA Salter (p. 496). 
 
 [ri. XXX, fig. 1: PI. XXXI, ngs. 3, 3a-c; and PI. XXXV, figs. 4, 4a-b.l 
 
 Figure 1. Cast of (he interior of a ventral valve compressed in the shale of Division Ic of Matthew [1886, p. 82], 
 
 in New Brunswick (locality not given). University of Toronto, Canada. Specinicii fi{;urcd by 
 
 Matthew [1886, PI. V, fig. 9d] as Limjuldla dawsoni. 
 la. Ventral and dorsal valves from Locality 3011, Middle Cambrian .shales of Division Id of Matthew on 
 
 Porters Brook, St. John County, New Brunswick. University of Toronto, Canada. Specimens 
 
 figured by Matthew [1880, PI. V, figs. 8, 8a-b] as Linguhlla lingnloides. 
 lb and Ic. Ventral and dorsal valves shown in figure la. University of Toronto, Canada. 
 Id. Ventral valve from Locality 301k, Middle Cambrian, St. John formation in St. John, Xew Brunswick. 
 
 Cornell University, Ithaca, N. Y. Specimen figured by W'alcott [1884a, PI. V,Tig. 8J as Lingulaf 
 
 dawsoni. 
 le. Small exfoliated ventral valve from Locality la. Middle Cambrian shale on Manuels Brook, Conception 
 
 Bay, Newfoundland. U. S. Nat. Mus. Cat. No. 51757a. 
 If. Distorted ventral valve from Localitj- 2, Middle Cambrian shales on Manuels Brook, Conception Bay, 
 
 Newfoundland. U. S. Nat. Mus. Cat. No. 56997a. 
 Ig. Cast of the exterior of a distorted ventral valve, associated with the specimen represented by figure If. 
 
 U. S. Nat. Mus. Cat. No. 56997b. 
 Ih. Interior of part of a dorsal valve, associated with specimen represented by figure If. U. S. Nat. Mus. Cat. 
 
 No. 56997c. 
 li. Slightly distorted dorsal valve as.sociated with specimen represented by figure If. U. S. Nat. Mus. Cat. 
 
 No. 56997d. 
 ]j. Unusually convex and well-preserved ventral A'alve associated with specimen represented by figure If. 
 
 U. S. Nat. Mus. Cat. No. 56997e. 
 Ik. Exfoliated, slightly distorted ventral valve, associated with specimen represented by figure If. U. S. 
 
 Nat. Mus. Cat. No. 56997f. 
 11. Partly exfoliated ventral valve from the limestones int<'rbedded in the shales of Locality 1, Middle 
 
 Cambrian, Manuels Brook, Conception Bay, Newfoundland. The peculiar appearance of what is 
 
 shown of the interior of the shell is partly explained by figure lo, which is compressed in the shale. 
 
 U. S. Nat. Mus. Cat. No. 51756c. 
 Im. Ventral valve, associated with specimen represented by figure 11. A portion of the outer surface is 
 
 exfoliated so as to show the characteristic markings of the inner surface. U. S. Nat. Mus. Cat. 
 
 No. 51756d. 
 In. Cast of a dorsal valve showing the cast of a median septum and area, from Locality la, Middle Cambrian 
 
 sandy .shale 50 feet lower in the .section than specimens represented by figures 1 1 and 1 in, on Manuels 
 
 Brook, Conception Bay, Newfoundland. L". S. Nat. Mus. Cat. No. 517o7b. 
 lo. Cast of the interior of a ventral valve showing the area of a portion of the ^'isceral cavity. From Locality 
 
 1, Middle Cambrian shale, Manuels Brook, Conception Bay, Newfoundland. V . S. Nat. Mus. Cat. 
 
 No. 51756a. 
 Ip. Very nearly perfect dorsal valve, a.ssocialed with the specimen represented by figure I 1. U. S. Nat. 
 
 Mus. Cat. No. 51756e. 
 Iq. Cast of Ihe interior of a dorsal valve associated with the specimen represented by figure 1 1. U. S. Nat. 
 
 Mus. Cat. No. 5175Gf. 
 Ir. Interior of a dorsal valve, .showing vascular sinus and median septum; also the ridges bounding the path of 
 
 advance of the central scars. .\,ssociated with the specimen represented by figure 1 1. I'. S. Nat. 
 
 Mus. Cat. No. 51756g. 
 Is. Cast of the interior of a dorsal valve from Locality 1, Middle Cambrian .shale on Manuels Brook, Concep- 
 tion Bay, Newfoundland. U. S. Nat. Mus. Cat. No. 51756b. 
 It. Ventral valve, laterally compressed, preserving the fine surface markings <lescribed in the text. Collected 
 
 from Locality 6g, Middle Cambrian limestone, Chappie Arm, Trinity Bay, Newfoundland. U. S. Nat. 
 
 Mus. Cat. No. 51759a. 
 lu. Cast showing part of the interior of a ventral valvr fnmi Locality 308, Upper Cambrian shales of Division 
 
 C3c of Matthew's section at Navy Island, St. John Harbor. NewBrtuiswick. I'niversity of Toronto. 
 
 The specimen represented by figure lu was illustrated by Matthew [1892, PI. XII, fig. 8bJ as Obulcltaf 
 
 (jemmula. 
 102 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XXIX 
 
 FRANCES WIESER DEL. 
 
 MELlOTVPE CO BOSTON 
 
PLATE XXIX. 103 
 
 LiNGULELLA FERRUGiNEA Salter — Continued. 
 
 Figure Iv. Cast showing part of the interior of a dorsal valve associated with the specinn-n n-iiresenled by figure lu. 
 
 The outlines of a pedicle groove were produced by accidental fractures in the shell. University of 
 
 Toronto. Specimen illustrated by Matthew [1892, PI. Xll, fig. 8c] as Obolella? gemmula. 
 Iw. Compressed ventral valve associated with Obolus refidgens in Locality 308, Upper Cambrian shales of 
 
 Division C3c of Matthew's section, Navy Island, St. Juhn Harbor, New Brunswick. University of 
 
 Toronto. 
 2. ^■eut^al ? valve from Locality 318h, Middle Cambrian shales at St. Da\ids, South Wales. Copied from 
 
 Ilicks's figure [Salter and Hicks, 18G7, fig. 2, p. 340] of Lingulella femiginea oralis. 
 2a. Enlarged view of the valve represented by figure 2. Copied from Salter and Hicks [1867, fig. 3, p. 340]. 
 2b. Ventral valves from Locality 318j, Middle Cambrian at Pen-y-pleidiau, St. David.s, South Wales. Copied 
 
 from Salter's figure [Salter and Hicks, 1867, fig. 1, p. 340] of Limjitlclla/a-niginea. It represents the 
 
 type specimen. 
 2c. Ventral? valve from Locality 318v, Upper Cambrian, Rhiwfelyn, North Wales. Copied from Davidson 
 
 [1868, PI. XV, fig. 7a]. " 
 2d. Ventral valve from Locality 318u, Upper Cambrian, Gwerny-y-Barcud, Norlh Wales. Cupied from David- 
 son [1868, PI. XV, fig. 6a]. 
 2e. Distorted ventral valve from Locality 366b, Middle Cambrian at Porlhclais Harbor, .south of St. Davids, 
 
 South Wales. Copied from Davidson [1871, PI. XLIX, fig. 3.5a]. 
 2f. Distorted veptral valve from Locality 318h, Middle Cambrian Menevian shales at St. Davids, South Wales. 
 
 Copied from Davidson [1871, PI. XLIX, fig. 33a]. 
 
 Lingulella billingsiana (Whiteaves) (j). 4S3). 
 
 Figure.? 3 and 3a. Ventral valves, from Locality 314a, Upper Cambrian shales on Kelleys Island, Conception Bay, 
 Newfoundland. Drawn from the type material in the Museum of the Geological Survey of Canada. 
 Whiteaves [1878, p. 226] did not figure the specimens on which he based his species. Figure 3a 
 may be taken as the type. 
 
 Lingulella buttsi Walcott (p. 484). 
 
 Figure 4. Dorsal valve, the type specimen, from Locality 90c, Middle Cambrian Conasauga limestone near Kimbrel, 
 Bibb County, Alabama, showing the slight median flattening of the surface and backward curvature 
 of the concentric striae. U. S. Nat. Mus. Cat. No. 51779a. Copied from Walcott [1908d, PI. VIII, 
 fig. 6]. 
 
 4a and 4a'. Exterior view and side outline of ventral valve from Locality 90b, Middle Cambrian Conasauga 
 limestone near Woodstock, Bibb County, Alabama. U. S. Nat. Mus. Cat. No. 51778a. 
 
 4b and 4b'. Partly exfoliated ventral valve associated with the shell represented by figure 4a, showing the 
 cast of the ridges along the path of advance of the muscle scars on each side of the \'isceral area. 
 U. S. Nat. Mus. Cat. No. 51778b. 
 
 Delgadella lusitanica (Delgado) (p. 500). 
 
 Figure 5. Cast of the interior of a ventral valve, the type specimen. The marginal rim indicates the thickness of 
 the shell. 
 5a. Cast of the interior of a ventral valve. 
 5b. Cast of a ventral valve. 
 
 The specimens represented are all from Locality 351, Lower Cambrian shales at Monte de Valbom, northeast of 
 Villa Boim, Province of Alemtejo, Portugal. The figures (5, 5a, and 5b) are reproduced from photographs sent to me 
 by M. Delgado of the specimens figured by him [1904, PI. IV, figs. 34, 31, and 32, respectively] under the name of 
 Lingulepis lusitanica. Each of the views in this monograph is the reverse of the corresponding one given by Delgado. 
 
 Lingulella delgadoi Walcott (p. 491). 
 
 Figure 6. Cast of exterior of ventral valve, the type specimen. 
 6a. Cast of interior .of ventral valve. 
 
 Figures 6 and 6a are reproduced from photographs sent to me by M. Delgado of the specimens figured by him 
 [1904, PL IV, figs. 16 and 18, respectively] under the name of Lingulella granvillensis. 
 
 Figure 6b. Cast of dorsal valve showing exterior surface. Reproduced from a photograph sent to me by M. Delgado 
 of the specimen figured by him [1904, PI. IV, fig. 27] under the name of Lingulepis acuminata meeki. 
 The -^dew in this monograph is the reverse of that given by Delgado. 
 6c. Cast of shell of dorsal valve partly broken away. Reproduced from a photograph sent to me by M. Delgado 
 of the specimen figured by him [1904, PL IV, fig. 14] under the name of Lingulella cf. liyiguloides. 
 The view in this monograph is the re\'erse of that given by Delgado. 
 
 The specimens represented by figures 6, 6a-c are from Locality 351, Lower Cambrian shales at Monte de Valbom, 
 northeast <if Villa Boim, Province of Alemtejo, Portugal. 
 
PLATE XXX. 
 
 105 
 
PLATE XXX. 
 
 LixGULELLA FERKUGixEA Salter? (p. 496). 
 
 |M. XXIX, figs. 1, la-w, 2, 2a-f; I'l. XXXI, figs. :!, 3a-c-; and I'l. X.KXV, fiKS. 4, Ja-b.] 
 
 FiGURK i. \enlral valv&s from Locality 389d, Upper Cambrian, at Iruya, Salta, Argentina. Copied from Kayser'e 
 figure [1897, PI. VII, fig. 7] of LinguhUn ci./erruginea. 
 
 LiNGULELLA DAVLSI (McCov) (]). 489). 
 [PI. XX.XI, figs. 6. la-h.) 
 
 Figure '.;. Dorsal valve, from Locality 389d, Upper Cambrian, at Iriiya, Salta, Argentina. Copied from Kayser [1897, 
 PI. VII, fig. 6]. 
 2a. Ventral and dorsal valves from Locality 332, I'lipor Cambrian limestone at Saimaki, Liaotung, China. 
 Copied from Kayser [1883, PI. Ill.'fig. 3]. 
 
 LixGULELLA NiCHOLSONi Callawav (p. 522). 
 
 Figure .3. Ventral valve, the type specimen, from Locality 3041, Upper Cambrian Shineton shales in South Shrop- 
 shire, England. Copied from Callaway [1877, PI. XXIV, fig, 11]. 
 3a. Enlargement of the area of a ventral valve from one of the localities mentioned in Locality 3041, South 
 
 Shropshire, England. Copied from Callaway [1877, PI. XXIV, fig. lib]. 
 3b. Dorsal valve with outer shell exfoliated except over the area. V. S. Xat. Mus. Cat. Xo. 5174Sa. 
 3c. Exfoliated dorsal valve. The central and transmedian muscle scars are drawn from another specimen. 
 
 U. S. Nat. Mus. Cat. Xo. 5174Sb. 
 3d. A small ventral valve showing outline of area. L^. S. Xat. Mus. Cat. Xo. 51748c. 
 3e. A small elongate dorsal valve. U. S. Nat. Mus. Cat. No. 5174Sd. 
 
 3f . A small ventral valve resting on the dorsal valve which has been pushed backward out of its natural 
 position. U. S. Nat. Mus. Cat. Xo. 51748e. 
 The specimens represented by figures 3b-f are from Locality 304 1, I'pper Cambrian Shineton shale, on Shineton 
 Brook and vicinity, South Shropshire, England. 
 
 LiNGtTLELLA cf. FEREUGIXEA (]). 500). 
 
 Figure 4. \'entral valve from Locality 345, Middle Cambrian shale on the Dlouhd Ilora, near Skrej, Bohemia. Copied 
 from Pompeckj's figure [189(ib, PI. XIV, figs. 16a-b] of " Lingulella {?) sp." 
 
 LiNGULELLA KltJEENSIS (WaagCIl) (p. 511). 
 
 Figure 5. Type specimen of Waagen's species "Lingula warthi." Geol. Survey India Cat. Xo. 3/79.5. Specimen 
 figured by Waagen [18S5, PI. LXXX^'I, figs. 9a-b] as Lingula (?) tfarlhi. The same specimen 
 is figured by Waagen [1891, PI. II, figs. 17a-b] as Lingula (f) Hurensis, hut from his description 
 [1885, pp. 769-770] this is the form to which he intended to give the name uarthi. I think it is the 
 dorsal valve of Lingulella Hurensis. 
 
 5a. Copy of the figures given by Waagen [1891, PI. II, figs. 17a-b] of the specimen represented by figure 5. 
 The cardinal slopes are crushed in, which gives the depressed slopes described by '\^'aagen [1885, 
 p. 769]. The front is also restored. 
 
 6. Type specimen of Lingula (f) hiurensis Waagen. Geol. Survey India Cat. Xo. 3794. Specimen figured 
 by Waagen [1SS5, p. 768, PI. LXXXVI, figs. Sa-b] as Lingula (?) hiurensis. The same specimen is 
 figured by Waagen [1891, PI. II, figs. ISa-b] as Lingula (f) warthi, but from his description [1885, 
 p. 768] this is the form to which he intended to give the name Hurensis. 
 
 6a. Copy of the figures given by Waagen [1891, PI. II, figs. 18a-b] of the specimen represented in figure 6. The 
 front of the shell is restored in \\'aagen's figures, and the cardinal slopes widened out so as to make a 
 diagrammatic figure. 
 The specimens represented are both from Locality 357. Middle Cambrian limestones in the Xeobolus beds of the 
 Khussak group, near Kiiira, Salt Range, India. 
 
 LiXGILELLA AVIRTHI (BaiTaiicle) (p. 541). 
 
 Figure 7. \'entral valve from Locality 303c, passage beds between the Upper ('aml)rian and Ordovician near Hof, 
 Bavaria. Enlarged one-third. Type specimen, copied from Barrande [1868a, fig. 63]. 
 
 LiNGULELLA CEDENS (BaiTande) (p. 485). 
 
 Figure 8. Ventral valve from Locality 303c, passage beds between the Upper Cambrian and (Jrdnvician near Hof, 
 liavaria. Enlarged unc-third. Tvpe specimen, copied from Barrande [lS6Sa, fig. CO]. 
 106 ■ 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XXX 
 
 19' 
 
 FRANCES WtESER DEL. 
 
 rtELIOTVoe CO BOSTON 
 
PLATE XXX. 107 
 
 LiNGULELLA? (LiNGULEPIS ?) SQUAMOSA (Holl; (p. 559). 
 
 Figure 9. Ventral valve from Locality 304g, Upper Cambrian Hollybush sandstones, Malvern Hills, England. Copied 
 from Davidson's figure [1S6G, PI. II, fig. 7] of Lingula squamosa. 
 
 LiNGULELLA (LiNGULEPIS?) PYGM^A (Salter) (p. 556). 
 
 Figure 10. Ventral? valve from Locality 304f, Upper Cambrian "Black shales," Malvern Hills, England. Copied 
 from Salter [186.5, figs. 8a-b, p. 101]. 
 
 LiNGULELLA siGNATA (Barraiide) (p. 532). 
 
 Figure 11. Dorsal? valve from Locality 303c, passage beds between the Upper Cambrian and Ordovician near Ilof, 
 Bavaria. Enlarged one-third. Copied from Barrande [1868a, fig. 73]. 
 
 LiNGULELLA? IIUMILLIMA (BaiTaiide) (p. 507). 
 
 Figure 12. Dorsal valve from Locality 303c, passage beds between the Upper Cambrian and Ordovician near Hof, 
 Bavaria. Enlarged one-third. Copied from Barrande [1868a, fig. 70]. 
 
 LiNGULELLA sp. undt. a Walcott (p. 541). 
 
 Figure 13. Dorsal valve from Locality 310k, Upper Cambrian limestone on Oeland Island, Sweden. IT. S. Nat. Mus. 
 Cat. No. .517-19a. 
 
 LiNGULELLA LINNARSSONI (Walcott) (p. 516). 
 
 Figure 14. Ventral valve, the type specimen, with the outer shell partly exfoliated. U. S. Nat. Mus. Cat. No. 3.52.57a. 
 14a. Enlargement of the exterior surface on the anterior portion of a ventral valve. L". S. Nat. Mus. Cat. No. 
 3.5257b. 
 The specimens represented are both from Locality 320n, Middle Cambrian limestone at Lovened, Djupadal, 
 Province of Skaraborg, Sweden. 
 
 LiNGULELLA AGNOSTORUM (WalleHus) (p. 476). 
 
 Figure 15. Ventral valve greatly enlarged, and longitudinal outline of valve, from Localitj- 3101, passage beds between 
 the Middle and Upper Cambrian, at Borgholm, Oeland Island, Sweden. U. S. Nat. Mus. Cat. No. 
 51747a. 
 
 Obolus ? zoppi Walcott (p. 422). 
 
 Figure 16. Ventral valve, the type specimen, from Locality 354f, Middle Cambrian sand.stone nrar Canal Grande, on 
 the road to Punta Pintau, Sardinia, Italy. Copied from Bornemann [1891, PI. XIX, fig. 17a]. 
 
 16a. Dorsal valve associated w-ith the shell represented by figure 16. Copied from Bornemann [1891, PI. XIX, 
 fig. 16]. 
 
 16b. Side \'iew of the shell represented in figure 16. Copied from Bornemann [1891, PI. XIX, fig. 17b]. 
 
 Obolus ? meneghinii Walcott (p. 403). 
 
 Figure 17. A small exfoliated ventral valve, the type specimen, from Locality 354c, Middle Cambrian .sandstone at 
 Punta Pintau (Canal Grande), Sardinia. Copied from Bornemann's figure [1891, PI. XIX, fig. 14a] of 
 Lingula pctalon. 
 17a. A large ventral valve from Locality 354e, Middle Cambrian shale at Porto Canal Grande, Sardinia. 
 Copied from Bornemann's figure [1891, PI. XIX, fig. 18] of OboleUa sp. 
 
 LiNGULELLA BORNEMANNI (Walcott) (p. 483). 
 
 Figures 18, 18a, and 18b. More or less distorted and compressed ventral valves from Localil y 354, Middle ? Cambrian, 
 Canal Grande, Sardinia. 
 Figures 18, 18a, and ISb are copied from Bornemann's figures [1891, PI. XIX, figs. 10a, 4, and 8, respectively] of 
 Lingula attenuata. Figure 18 represents the type specimen. 
 
 Figure 18c. Dorsal ? valve from Locality 354, Middle ? Cambrian, Canal Grande, Sardinia. Copied from Bornemann's 
 figure [1891, PI. XIX, fig. 7] of Lingula attenuata. 
 
108 PLATE XXX. 
 
 Obolus schmalenseei (Walcott) (p. 412). 
 
 Figure 19. Broad form of the ventral valve, showing cast of pedicle furrow and a portion of the visceral cavity. U. S. 
 
 Nat. Mus. Cat. No. 35291a. 
 19a. Exterior of dor.sal valve. U. S. Nat. Mu.s. Cat. No. 35291b. 
 19b. An elongate ventral valve. U. S. Nat. Mus. Cat. No. 35291c. 
 19c. Cast of a dorsal valve, showing the strongly marked area and niarginsof the posterior portion of the visceral 
 
 ca\-ity. U. S. Nat. Mus. Cat. No. 3529Jd. 
 19d. Partly exfoliated ventral and dorsal valves, the type specimen. U. S. Nat. Mu.s. Cat. No. 3529Ie. 
 19e. A small ventral valve. U. S. Nat. Mus. Cat. No. 3.5291f. 
 
 The specimens represented are all from Locality 8w, Middle Cambrian limestone at Andrarum, Province of 
 Christianstad, Sweden. 
 
 Elkania IDA (Billings) (p. 56.3). 
 
 [PI. Ll, figs. 4, 4a-c.l 
 
 Figure 20. A probable ventral valve, from Locality 319, Lower Ordo^^cian limestone of No. 1 of Billings's section, Point 
 Le\as, Quebec, Canada. Geol. Survey Canada. 
 20a. Dorsal valve from the locality represented by figure 20. Geol. Survey Canada. 
 
PLATE XXXI. 
 
 109 
 
PLATE XXXI. 
 
 a. Central lateral space of area, 
 a'. Outer lateral space of area. 
 c. Trapezoidal area, including central, middle 
 
 lateral, and outside lateral muscle scars. 
 f. Flexure line of area, 
 h. Central muscle scar. 
 
 I. Transmedian muscle scar. 
 
 j. Anterior lateral muscle scar. 
 
 1. Outside lateral muscle scar, 
 p. Pedicle groove. 
 V. Visceral cavity, 
 vs. Main vascular sinus. 
 
 LixGULELLA NATHORSTi Linnarssoii (p. 521). 
 
 Figure 1, Cast of the interior of ventral valve, from Locality 320x, Lower Cambrian lime.stonn at Andrariim, Province 
 
 of Christ ianstad, Sweden. U. S. Nat. Mtis. Cat. No. 18109a. 
 la and lb. Casts of the interior of dorsal valves associated with (he speeimen represented by figure 1. U. S. 
 
 Nat. llus. Cat. Nos. 18199b and 18199c, respectively. 
 Ic. Ventral valve preserving most of the shell, from I-ocality 8y, Lower Cambrian limestone at Skirosen, 
 
 Dalarne, Sweden. U. S. Nat. Mus. Cat. No. 517;»a. 
 Id and le. Dorsal valves associated with the ventral valve represented by figure Ir. IT. S. Nat. Mus. Cat. 
 
 Nos. 51739b and 51739c, respectively. 
 If. Ventral valve associated with the ventral valve represented by figure Ic. U. S. Nat. Mus. Cat. No. 51739d- 
 Ig and Ih. Dorsal valves associated with the ventral valve represented liy figure Ic. U. S. Nat. Mus. Cat. Nos. 
 
 51739eand 517301, respectively. 
 
 LiNGULELLA SIEMIKADZKII (W^alcott) (p. 5.31). 
 
 Figure 2. Ventral valve, the type specimen, showing; portion of the outer surface and the finely striated inner layer 
 of shell. U. S, Nat. Mus. Cat. No. 3525Sa. 
 2a. Cast of part of a dorsal valve. U. S. Nat. Mus. Cat. No. 3525Sb. 
 
 The specimens represented are both from Locality 368, Middle Cambrian quarlzitic sandstones in the Pepper Moun- 
 tains, near Sandomierz, on the Vistula, Russian Poland. 
 
 LiNGULELLA FEREUGINEA Salter (p. 406). 
 [PI. XXIX. tigs. 1, la-w, 2, 2a-f; PI. XXX, fig. 1: and PI. XXXV, figs. 4, Ja-b.J 
 
 Figure 3. Ventral valve from Locality 310p, Middle Cambrian limestone at Borgholm, Oeland Lsland, Sweden, 
 U. S. Nat. Mus. Cat. No. 51752a. 
 
 3a. Dorsal valve from Locality 310y, Middle Cambrian limestone of Kiviks Esperod, Province of Malmohus, 
 Sweden. V. S. Nat. Mus. Cat. No. 18205a. 
 
 3b. Short ventral valve from Locality 310z, Middle Cambrian limestone at Brantevik, Sweden, that is doubt- 
 fully referred to this species. U. S. Nat. Mus. Cat. No. 51750a. 
 
 3c. Ventral valve doubtfully referred to the species from Locality 330m, Middle Cambrian at Kinnekulle, 
 Province of Skaraborg, Sweden. Copied from Linnarsson's figure [1876, PL III, fig. 28]of "Xtn^u^a 
 or Ling'ileUa sp." 
 
 LixGi'LELLA LEPi.s (Salter) (p. 514). 
 
 Figure 4. Ventral valve from Locality 366k, Upper Cambrian shales, Penmorfa, Jlerioneth.shire, North Wales. 
 
 Enlarged drawing of the specimen represented in figure 4a. Copied from Davidson [1871, PL XLIX, 
 
 fig. 31a]. 
 4a. The ventral valve figured in figure 4, natural size. Copied from Davidson [1871, PI. XLIX, fig. 31]. 
 4b. Cast of the interior of a ventral valve from Locality 8x, pas.sage beds between the I'jiper Cambrian and the 
 
 Ordovician, at Slemmestad, near Chrisliania, Norway, showing area, cast of pedicle groove, and 
 
 visceral cavity. U. S. Nat. Mus. Cat. No. 51741a. 
 4c. Exterior of a strongly convex, highly polished ventral valve associated with tlie shell represented in figure 
 
 4b. . Traces of radiating ribs, so strongly developed in figure 4d,are visible with a strong lens. U. S. 
 
 Nat. Mus. Cat. No. 51741b. 
 4d. Dorsal valve associated with the shell represented in figure 4b. marked by strong radiating ribs and fine 
 
 concentric slriie. I^. S. Nat. Mus. Cat. No. 51741c. 
 4e. Narrow form of donsal valve, showing outline of elongate visceral cavity, from Locality 9f, Upper Cambrian 
 
 limestones at Ncrrsnies, west of Christiania, Norway. U. S. Nat. Mus. Cat. No. 51742a. 
 4f. Cast of part of a broad form of a dorsal valve associated with the shell represented by figure 4b. U. S. 
 
 Nat. Mus. Cat. No. 51741d. 
 110 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XXXI 
 
 FRANCES WIESER DEL. 
 
 riCLlOTVPE ;0 SSSTON 
 
PLATE XXXI. Ill 
 
 LiNGULKLLA? PRIM^VA Hicks (p. 527). 
 
 Figures 5 and 5a. Ventral? valves from the Middle? Cambrian Cacrfai group (see Locality 366c), soulh of ,Si. 
 Davids, South Wales. Copied from Davidson [ISKIi, PI. XVII, figs. .31 and 3.3, respectively]. Figure 
 oa represents the type specimen, Davidson's figure being a copy of the one given by liicks [1871, 
 PI. XV, tig. 1-1]. 
 
 LiNGXJLELLA DAVisi (McCoy) (p. 489). 
 
 [PI. XXX, figs. 2 and 2a.] 
 
 Figures 6 and 6a. Distorted ventral valves from "Lingula flags, Penmorfa, Tremadoc" (see localities 366k and 366 1;, 
 Merionethshire, North Wales. Copied from Davidson [IStiG, PI. IV, figs. 10 and 11, respectively]. 
 
 6b. Distorted ventral valve from Locality 317b, Middle Cambrian, at Bellewstown, County Meath, Ireland. 
 Copied from Davidson [1866, PI. IV, fig. 12]. 
 
 6c. Enlargement of the area of a cast of a ventral valve from Locality 366a, Upper Cambrian shales, 6 miles east 
 of Ffestiniog, Merionethshire, North Wales. U. S. Nat. Mus. Cat. No. 51740a. 
 
 6d. Cast of the interior of a distorted ventral valve associated with the specimen represented by figure 6c. 
 r. S. Nat. Mus. Cat. No. 51740b. Specimen figured by Walcott [189Sb, PI. XXVII, fig. 2] asObobjs 
 [Lingulella) davisii. 
 
 Be. Cast of the interior of a dorsal valve, showing the characteristic muscle scars of the genus. Locality 366n, 
 Upper Cambrian shales at Portmadoc, Merionethshire, North Wales. U. S. Nat. Mus. Cat. No. 
 35239a. Specimen figured by Walcott [1898b, PI. XXVII, fig. 4] as Obolus {Lingulella) davisii. 
 
 6f. Cast of the interior of a ventral valve a.ssociated with the shell represented in figure 6e, showing the out- 
 lines of the visceral cavity and the vascular sinuses. U. S. Nat. Mus. Cat. No. 35239b. Specimen 
 figured by Walcott [1898b, PI. XXVII, fig. 1] as Obolus (Lingulella) davisii. 
 
 6g. Cast of the interior of a ventral valve in which the characteristic punctate surface of the interior of the shell 
 is shown by the large pajjillae scattered over the surface. Locality 366a, Upper Cambrian shales 6 
 miles east of Ffestiniog, Merionethshire, North Wales. U. S. Nat. Mus. Cat. No. 51740c. 
 
 6h. Cast of a distorted dorsal valve associated with the shell represented in figure 6g, preserving the impressions 
 of the transmedian and outside lateral muscle scars. U. S. Nat. Mus. Cat. No. 51740d. Specimen 
 figured by W'alcott [1898b, PI. X'XVII, fig. 5] as Obolus (Lingulella) davisii. 
 
PLATE XXXII. 
 
 62667°— VOL 51, pt 2—12 8 113 
 
PLATE XXXII. 
 
 h. Central muscle scar. j. Anterior lateral muscle scar. 
 
 LiNGULELLA DAViDSONi (Barrancle) (p. 489). 
 Figure 1. Partly exfoliated ventral valve, the type specimen, showing lamellated shell, from Locality 303m, 
 
 Ordovician, Etage d4, at Lieben, Bohemia. Enlarged one-third. Copied from Barrande [1879b, 
 
 PI. CIV, fig. vni:lA]. 
 la. Side view of the specimen represented by figure 1. Copied from Barrande [1879b, PI. CIV, fig. viii:lb]. 
 lb. Less elongate ventral valve than that represented by figure 1, from Locality 303n, Ordovician, Etage 
 
 d4, at Wraz, Bohemia. Enlarged one-third. Copied from Barrande [ISTOb, PI. CIV, fig. vin:.3A]. 
 Ic. Side view of the specimen represented by figure lb. Copied from Barrande [1879b, PI. CIV, fig. viii:3b]. 
 Id. Enlargement of the area and posterior portion of figure le. Copied from Barrande [1879b, PI. CIV, fig. 
 
 vm:4E]. 
 le. Interior of a ventral valve from Locality 303o, Ordovician, Etage d4, at Lodenitz, Bohemia. Copied from 
 
 Barrande [1879b, PI. CIV, fig. vni:4]. 
 
 LiNGULELLA? iNsoNS (Barrande) (p. 508). 
 
 Figure 2. Interior of ventral valve from Locality 303d, Lower Ordovician, Etage dl, at Swarow, Bohemia. Copied 
 from Barrande [lS79b, PI. CV, fig. .x:4A]. 
 
 2a. Partly exfoliated dorsal valve from same bed as specimen represented by figure 2. Copied from Bar- 
 rande [1879b, PI. CV, fig. x:3A]. 
 
 2b and 2c. Interior of ventral valves, showing area, from Locality 303e, Lower Ordovician, Etage dl, at Sta. 
 Benigna, Bohemia. Copied from Barrande [1879b, PL CV, figs. x:5A and x:CA, respectively]. 
 Figure 2c represents the type specimen. 
 
 2d. Enlargement of the area of figure 2c. Copied from Barrande [1879b, PL CV, fig. x:6E]. 
 
 2e. Enlargement of surface of shell and impression of interior surface from the anterior portion of the valve. 
 Locality 303d, Lower Ordovician, Etage dl, at Swarow, Bohemia. Copied from Barrande [lS79b, 
 PL CV, fig. x:lf]. 
 
 LiNGULA? EXiMiA Barrande (p. 301). 
 Figure 3. Fragment of the shell greatly enlarged to show complex character of the surface ornamentation. Inserted 
 for comparison. Locality 3031, Lower Ordovician, Etage dl, at Libetschov, Bohemia. Copied from 
 Barrande [lS79b, PI. CV, fig. i:f]. 
 
 LiNGULELLA? SIMPLEX (BaiTaiide) (p. 534). 
 
 Figure 4. Ventral valve showing portion of area where the tliin shell has been pressed down into it. Locality 303p, 
 Lower Ordovician, Etage d3, near Beraun, Bohemia. Copied from Barrande [lS79b, PI. CIV, fig. 
 vi:lA]. 
 
 4a. Dorsal valve from Locality 303a, Lower Ordovician, Etage d3, at Trubin, Bohemia. Copied from Bar- 
 rande [1879b, PL CIV, fig. vi:4A]. 
 
 4b. Side view of specimen represented by figure 4a. Copied from BarnuKle [lS79b, PI, t'lV, fig. vi:4B]. 
 
 Obolus (Paljeobolu.'^ ) BRETONENSis (Matthew) (p. 426). 
 
 Figure 5. Cast of the interior of a flattened ventral vah-e, the type specimen, slightly compressed laterally. I'niversity 
 of Toronto, Canada. Reproduced from a photograph of one of Matthew's. specimens; it may be the one 
 used by him in drawing figure 2b of his paper [1903, PI. IX], but closer identification is impossible. 
 5a. Cast of part of the interior of a ventral valve. University of Toronto, Canada. 
 
 5b. Exterior of a nearly entire dorsal valve. University of Toronto, Canada. Reproduced from a photograph 
 of one of JIatthew's specimens; it may be the one used by him in drawing figure 2(1 of his paper 
 [1903, PL IX]. 
 5c. Exterior of a dorsal valve, showing finely preserved outer surface. University of Toronto, Canada. Repro- 
 duced from a photograph of one of Matthew's specimens; it may be the one used by him in drawing 
 figure 2a of his paper [1903, PI. IX]. 
 5d. Cast of part of a broken dorsal valve in which the area is preserved. University of Toronto, Canada. 
 5e. Enlargement of a cast of the interior of a dorsal valve. L^niversity of Toronto, Canada. Reproduced from 
 a photograph of one of Matthew's specimens; it may be the one used by him in drawing figure 2e of his 
 paper [1903, PI. IX]. 
 The exact locality represented by the specimens figured is not known. It is probable, however, that ihey were 
 all collected at the type locality (344b), Middle Cambrian shales of Division E3d of Matthew's Etcheminian, Dugald 
 Brook, Cape Breton, Nova Scotia. 
 
 Figures .Sf and og. Exterior of nearly perfect ventral and dorsal valves, from Locality lOp, Middle Cambrian sand- 
 stones of Division E2b of Matthew on Dugald Brook, Cape Breton, Nova Scotia. U. S. Nat. Mus. 
 Cat. Nos. 51664a and ■■)1664b, respectively. 
 114 
 
U, S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XXXII 
 
 FRANCES WIESER DEL. 
 
 LIOTVPC CO BOS1 
 
PLATE XXXIII. 
 
 115 
 
PLATE XXXIII. 
 
 LiNGULELLA LENS (Matthew) (p. 512). 
 
 Figure 1. ^"entral valve broken and embedded in limestone. University of Toronto, Canada. TjTie epecimen, 
 
 figured by Matthew [1901, PI. V, fig. 3a] as Lingula f lens. 
 la. Ventral valve showing outline of a smaller shell than that rf'jire.^ontcd by figure 1. U. S. Nat. Mus. Cat. 
 
 No. 51767a. 
 lb, Ic, and Id. Partly e.xfoliated dorsal valves varying somewliat iii oulliue and size. V. S. Nat. Mus. 
 
 Cat. Nos. 517G7b, 5]7f)7c, and 51767d, respectively. 
 
 The specimens represented are all from Locality lOr, Upper Camlirian slialcs of Division C3a? of Matthew, at 
 McAdam Shore, East Bay, Cape Breton, Nova Scotia. 
 
 LiNGULELL.v coNCixx.A. Mattliew (p. 4S6). 
 
 (PI. XXXIV, figs. 1, la-r.] 
 
 Figure 2. Ventral valve broadened by movement in the fine shalo of Locality 3h, Upper Cambrian, McNeil Brook, 
 
 Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. No. 51762s. 
 2a. Ventral valve that occurs on the same hand specimen with the shell represented by figure 2. It has been 
 
 elongated by the movement which broadened figure 2. V. S. Nat. Mus. Cat. No. 51762t. 
 2b. ^'entral valve associated with the shell represented by figure 2, preserving its original outline. U. S. 
 
 Nat. Mus. Cat. No. 51762u. (See note following description of fig. 2h.) 
 2c. Small dorsal valve associated with the specimen represented by figure 2. U. S. Nat. Mus. Cat. No. 51762v. 
 2d. Dorsal valve, the type specimen, slightly broadened by compression; from Locality 307, Upper Cam- 
 brian, McLeod Brook, Cape Breton, Nova Scotia. University of Toronto, Canada. Drawn from one 
 
 of the specimens figured by Matthew [1901, PI. V, figs. 2a-b], but closer identification is impossible. 
 2e. Dorsal valve associated with the specimen represented by figure 2, slightly broadened by compression. 
 
 U. S. Nat. Mus. Cat. No. 51762w. 
 2f. Dorsal valve associated with the specimen represented by figure 2, more or less distorted by compression in 
 
 the shale. U. S. Nat. Mus. Cat. No. 51762x. 
 2g. Distorted dorsal valve from Locality 372, Upper Cambrian shale at Upper Lcitches Creek, Cape Breton, 
 
 Nova Scotia. U. S. Nat. Mus. Cat. No. .52449a. 
 2h. Dorsal valve associated with the ventral valve represented by figures 2 and 2b. U. S. Nat. Mus. Cat. 
 
 No. 51762y. Figures 2b and 2h preserve the original convexity and outline of the shell more 
 
 perfectly than those compressed in the fine shales. 
 
 Obolus (Westonia) ELt.A (Hall and Whitfield) (p. 455). 
 
 (PI. XLVir, figs. 1, la-p.) 
 
 Figures 3 and 3a. Associated dorsal valves distorted by movement in shale, one being broadened, and the other 
 elongated. U. S. Nat. Mus. Cat. Nos. 51684a and 51684b, respectively. 
 3b and 3c. Dorsal and ventral valves compressed and distorted in fine shale. U. S. Nat. >Ius. Cat. Nos. 
 51684c and 51684d, respectively. 
 
 The figures all represent specimens from Locality 3c, Middle Cambrian shales near Ophir, Utah, and are intro- 
 duced to illustrate the forms this species may often take where the fine shells have been more or less compressed and 
 stretched. They should be compared with the prevailing form of the species as shown on Plate XLVIL 
 
 LiNGULELLA (LiNGULEPIS) EXIGCA (Mattlll'W) (p. 551). 
 
 [PI. XLHI, figs. 1, la-z.] 
 
 Figure 4. Group of young shells occurring in fine, arenaceous shale, Locality 31, Middle Cambrian on McLean Brook, 
 1.5 miles west of Marion Bridge, Cape Breton, Nova Scotia, in which the adult specimens represented 
 on Plate XLIII occur. U. S. Nat. Mus. Cat. No. 34761s. 
 4a. Specimen in which the substance of the shell has been etched by acid so as to leave in relief the siliceous 
 matter filling the fractures in the shell. Locality 10s, Middle Cambruin sandstone on McLean 
 Brook, near Marion Bridge, Cape Breton, Nova Scotia. \J. S. Nat. Mus. Cat. No. 5246Sa. The 
 original specimen is 12 mm. in length. The system of fractures is very complicated within the two 
 main lines of fracture which cross each other obliquely, forming rhomboidal spaces. 
 IIG 
 
MONOGRAPH LI PL. XXXIII 
 
 U. 3. GEOLOGICAL SURVEY 
 
 FRANCES WIESER DEL. 
 
 MELIOTVPE CO eOSTOM 
 
PLATE XXXIV. 
 
 117 
 
PLATE XXXIV. 
 LiNGULELLA coNCiNNA Matthew (p. 486). 
 
 [I'l. XXXIII, figs. 2, 2a-h.) 
 
 Figure 1. This ventral valve is somewhat doubtfully referred to this species. The specimen from which the figure 
 was drawn occurs in Locality 310h, Upper? Cambrian shales in the Province of Skane, Sweden, and 
 is more nearly related to some forms of Lingulella concinna than to other species from the Upper 
 Cambrian and Lower Ordovician. U. S. Nat. Mus. Cat. No. 14932a. 
 
 la-h. Ventral valves illustrating variations in outline, convexity, etc., from Locality 3h, Ujiper Cambrian 
 shale on McNeil Brook, Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. Nos. 517G2a-h, re.spectively. 
 
 li-q. Dorsal valves associated with the ventral valves represented by figures la-h. L'. S. Nat.Mua. Cat. Nos. 
 51762i-q, respectively. 
 
 Ir. Three ventral valves and fragments of a dorsal valve associated with the shells represented by figures la-q 
 (X 2). U. S. Nat. Mus. Cat. No. 51762r. 
 
 Obolus septalis (Walcott) (p. 414). 
 
 [I'l. XXIII, fie. 3d.] 
 
 Figure 2. Exterior of dorsal valve. Collection of Mr. Byron E. Walker, Toronto, Canada. 
 
 2a. Cast of interior of dorsal valve, the type specimen. V. S. Nat. Mus. Cat. No. 51612a. 
 
 The specimens are both from Locality 14s, Middle Cambrian Ogygopsis zone on Mount Stephen, British Columbia. 
 Lingulella (Lingulepis) acuminata (Conrad) (p. .545). 
 
 [PI. XL, figs. 1, la-s; PI. XLI, figs. 1, la-n; and PI. XLII, figs. 1, la-o.] 
 
 Figure 3. Ventral valve with the apex worn off, from Locality 7z, Upper Cambrian limestone about 3 miles southeast 
 
 of Emigrant Pass, Esmeralda County, Nevada. IT. S. Nat. Mus. Cat. No. 51884a. 
 3a. Ventral valve intermediate in form between specimens represented by figures 3 and 3b, from Locality 7y, 
 
 Upper Cambrian limestones 2.5 miles southeast of Emigrant Pass, Esmeralda County, Nevada. U. S. 
 
 Nat. Mus. Cat. No. 56967a. 
 3b. Broad form of ventral valve with apex broken off, from Locality 7x, L'pper Cambrian limestones 2.5 milca 
 
 southeast of Emigrant Pass, Esmeralda County, Nevada. L'. S. Nat. Mus. Cat. No. 56967b. 
 3c and 3d. Dorsal valves associated with the shell represented by figure 3. U. S. Nat. Mus. Cat. Nos. 51884b 
 
 and 51884c, respectively. 
 3e. A small, slender ventral valve associated with the shell represented by figure 3. U. S. Nat. Mus. Cat. No. 
 
 51884d. 
 118 
 
U, S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XXXIV 
 
 ^V.! 
 
 FflANCES WIESER OEL. 
 
 MELtOTVPE CO BOSTOM 
 
PLATE XXXA 
 
 T 
 
 119 
 
PLATE XXXV. 
 
 a. Central lateral space of area. p. Pedicle groove, 
 
 a'. Outer lateral space of area. s. Median septum. 
 
 f. Flexure line of area. v. Visceral cavity. 
 
 h. Central muscle scar. vs. Main vascular sinus, 
 j. Anterior lateral muscle scar. 
 
 LiNGtXELLA coLLiciA (Matthew) (p. 486). 
 
 Figure 1. Exterior of an imperfect ventral valve, the type gpecimen. University of Toronto, Canada. 
 
 la. Partly exfoliated ventral valve, showing ^-isceral area and vascular sinuses. University of Toronto, 
 Canada. 
 
 lb. Crushed and broken cast of the interior of a ventral valve. University oi Toronto, Canada. 
 The specimens represented by figures 1, la-b are from Locality 13n', Middle Cambrian sandy shales of Division 
 E3e, Dugald Brook, Cape Breton, Nova Scotia. The figures are drawn from three of the specimens illustrated by Mat- 
 thew [1899b, PI. I, figs. 3a-e], but closer identification is impossible. 
 
 Figure Ic. Exterior of a dorsal \alve broadened and distorted by compression. Locality 13m, Middle Cambrian 
 
 sandstones of Division E3f, Gillis Brook, Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. No. 51772a. 
 Id. Imperfect cast of interior of a dorsal valve from Locality 13n', Middle Cambrian sandy shales of 
 
 Division E3e, Dugald Brook, Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. No. 524.53a. 
 le. Imperfect cast of interior of a flattened dorsal valve from Locality lOp, Middle Cambrian sandy shales 
 
 of Division E2b, Dugald Brook, Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. No. 35294a. 
 If. Cast of the interior of a ventral valve associated with the shell represented in figure le. U. S. Nat. Mus. 
 
 Cat. No. 3.5294b. 
 2. Cast of interior of ventral valve from Locality ISm, Middle Cambrian sandstones of Division E3f, Gillis 
 
 Brook, Cape Breton, Nova Scotia, showing area and position of vascular sinuses. U. S. Nat. Mus. 
 
 Cat. No. 57084a. 
 2a. Exterior of a slightly distorted ventral valve associated with the specimen represented by figure 2. U. S. 
 
 Nat. Mus. Cat. No. 57084b. 
 2b. Broad ventral valve, doubtfully referred to this species, from Locality lOp, Middle Cambrian sandy shales 
 
 of Di\dsion E2b, Dugald Brook, Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. No. 57083a. 
 2c. Dorsal valve associated with the specimen represented by figure 2a. U. S. Nat. Mus. Cat. No. 57084c. 
 2d. Interior of a dorsal valve associated with the specimen represented by figure 2a, showing a strong median 
 
 ridge and the position of the central muscle scars. U. S. Nat. Mus. Cat. No. 57084d. 
 
 Figures 2, 2a-d represent forms corresponding to those referred by Matthew [1903, pp. 114-115] to Leptobolus 
 collicia collis. 
 
 LiNGULELLA CANIA (Walcott) (p. 484). 
 
 Figures 3 and 3b. Casts of the interior of ventral valves from Locality 3i, Middle Cambrian sandy shale on McLean 
 Brook, 1.5 miles west of Marion Bridge, Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. Nos. 52451a 
 and 52451c, respectively. Figure 3 represents the type specimen. 
 3a. Partly exfoliated ventral valve associated with the shells represented in figures 3 and 3b. U. S. Nat. 
 
 Mus. Cat. No. •52451b. 
 3c. Exterior of dorsal valve from Locality IDs, Middle Cambrian sandstone on McLean Brook, near Marion 
 Bridge, Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. No. 35295a. 
 • 3d. Cast of interior of dorsal valve associated with the specimens represented by figures 3 and 3b. U. S. Nat. 
 ilus. Cat. No. 52451d. 
 
 LiNGULELLA FERRUGixEA Salter (p. 496). 
 
 [PI. XXIX, tigs. 1, la-w, 2, 2a-f: PI. XXX, fig. 1; and PI. XXXI, figs. 3, 3a-c.l 
 
 FiGURE.s 4 and 4a. Partly exfoliated ventral valves, showing cast of the area and pedicle ftirrow, from Locality 3h, 
 Middle Cambrian arenaceous shales, McNeil Brook, 1.5 miles east of Marion Bridge, Cape Breton, 
 Nova Scotia. U. S. Nat. Mus. Cat. Nos. 517.58a and 517.5.Sb, respectively. 
 4b. Dorsal valve associated with the ventral valves represented by figures 4 and 4a. U. S. Nat. Mus. Cat. 
 No. 517.58c. 
 120 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XXXV 
 
 FRANCES WIESER DEL. 
 
 neuiOTvpe ro bcston 
 
PLATE XXXV. 121 
 
 LiNGULELLA ATAVA (Miltthow) (p. 479). 
 
 Figure 5. Exterior of ventral valve from Locality 13n', Middle Cambrian sandstones of Division E3e, Dugald Brook, 
 
 Cape Breton, Nova Scotia. Type specimen, figured by Matthew [1899b, PI. II, fig. la] as Leplobolus 
 
 atavus. 
 5a and 5b. Partly exfoliated ventral valves, showing area, pedicle furrow, and outline of visceral cavity. 
 
 Locality lOp, Middle Cambrian sandstones of Division E2b, Dugald Brook, Cape Breton, Nova Scotia. 
 
 U. S. Nat. Mus. Cat. Nos. 35293a and 35293b, respectively. 
 5c. Dorsal valve associated with the specimens represented by figure 5. University of Toronto, Canada. 
 
 Specimen figured by Matthew [1899b, PI. II, fig. Id] as Leplobolus alarus. 
 5d. Cast of interior of dorsal valve, showing outline of visceral area, position of anterolateral muscle scars, 
 
 vascular sinuses, and area. Locality 13n', Middle Cambrian sandy shales of Division E3e, Dugald 
 
 Brook, Cape Breton, Nova Scotia, "u. S. Nat. Mus. Cat. No. 524.50a. 
 5e. Dorsal valve. The specimen can not now be located. It was in the collections of the United States 
 
 National Museum, but the locality is unknown. 
 5f, 5g, and 5h. Casts of laterally compressed dorsal valves associated with the ventral valves represented by 
 
 figures 5a and 5b. U. S. Nat. Mus. Cat. Nos. 35293c, 35293d, and 35293e, respectively. 
 
 LiNGULELLA FLUMENis (Matthew) (p. 500). 
 
 Figure 6. Exterior of imperfect ventral valve. University of Toronto, Canada. Type specimen, figured by Matthew 
 
 [1903, PI. XI, fig. 7a] as Leplobolus flumenis. 
 Ga. Interior of dorsal valve. University of Toronto, Canada. Specimen figured by Matthew [1903, PI. XI, 
 
 fig. 7b] as Leplobolus flumenis. 
 6b. Cast of interior of dorsal valve. University of Toronto, Canada. Specimen figured by Matthew [1903, 
 
 PI. XI, fig. 7e] as Leplobolus flumenis. 
 
 The specimens represented are all from Locality 325a, Middle Cambrian shales of Division C2c on McNeil Brook, 
 Cape Breton, Nova Scotia. 
 
 LiNGULELLA TORRENTis (Matthew) (p. 5.35). 
 
 Figure 7. Ventral valve from Locality 344f , Middle Cambrian shales of Matthew's Coldbrook gioup, Dugald Brook, Cape 
 Breton, Nova Scotia. University of Toronto, Canada. Type specimen, figured by Matthew [1903, 
 PI. VI, lig. 1] as Leplobolus lorrentis. 
 
 LiNGULELLA ATAVA INSULA (Matthew) (p. 4S0J. 
 
 Figures 8 and Sa. Ventral and dorsal valves from Locality 307d, Middle Cambrian sandy limestone ot Division E2a?, 
 at Youngs Point near George River Station, Cape Breton, Nova Scotia. Universitj' of Toronto, Canada. 
 Specimens figured by Matthew [1903, PI. VI, figs. 4a and lb] as Leplobolus alavus insutiv. Figure 8 
 represepts the type specimen. 
 
 LiNGULELLA ORA (Walcott) (p. 522). 
 
 Figure 9. Exterior of a broken \entral valve, the type specimen, from Locality 9p, Upper Cambrian limestone, 15 
 
 miles northwest of Fort Sill, Comanche County, Oklahoma. U. S. Nat. Mus. Cat. No. 51794a. 
 9a and 9a'. Top and side \'iew3 of a partly exfoliated ventral valve which illustrates the thickness of the 
 
 shell, from Locality 9q, Upper Cambrian limestone, 15 miles northwest of Fort Sill, (_'omanche County, 
 
 Oklahoma. U. S. Nat. Mus. Cat. No. 51795a. 
 9b and 9b'. Top and side views of a ventral valve associated with the shell represented in figure 9, showing 
 
 the outer surface of one of the inner layers of the shell. U. S. Nat. Mus. Cat. No. 51794b. 
 9c and 9c'. Top and side views of an elongate dorsal valve as.sociated with the shell represented in figure 9. 
 
 U. S. Nat. Mus. Cat. No. 51794c. 
 9d. Short broad form of dorsal valve associated with the shell represented in figure 9. U. S. Nat. Mus. Cat. 
 
 No. 51794d. 
 
PLATE XXXVI. 
 
 123 
 
PLATE XXXVI. 
 
 c. Trapezoidal area, including central, middle p. Pedicle groove, 
 
 lateral, and outside lateral muscle scars. .s. Median scjitum. 
 
 g. Umbonal muscle scar. v. Visceral cavity, 
 
 h. Central muscle scar. vs. Main vascular sinus, 
 
 i. Transmedian muscle scar. ivs. Lateral branches of vascular system, 
 
 j. -\nterior lateral muscle scar. pvs. Peripheral branches of vascular system. 
 
 k. Middle lateral muscle scar. x. Ilcart-shapeil cavity. 
 1. Outside lateral muscle scar. 
 
 Obolus selwyni (^^atthe\v) (p. 413). 
 
 [PI. .K.KXVII. figs. 1, la-f.] 
 
 Figure 1. luterior of a dorsal valve, showing a portion of the visceral area and adjoining parts; al.so the striation of 
 
 one of the inner layers of the shell. University of Toronto, Canada. Redrawn (with fig. If) from the 
 
 specimens on which Matthew [1903] based the diagrammatic figures in the left-hand figure on page 
 
 117 and figures la and Ic of Plate VII of his paper, 
 la. Exfoliated ventral valve, showing the visceral area and adjoining portions of the interior of the shell. 
 
 University of Toronto, Canada, 
 lb. Side outline of specimen represented by figure la. 
 Ic. Interior of a ventral valve, longitudinally compressed, which emphasizes the main vascular sinuses and 
 
 the lateral branches of the vascular system. University of Toronto, Canada. Redrawn (mth fig. I) 
 
 from the specimens on which Matthew [1903] based the diagrammatic figures in the left-hand figure 
 
 on page 117 and figures la and Ic of Plate VII of his paper. 
 Id. Interior of a dorsal valve, shomng portions of the vascular system. University of Toronto, Canada. 
 le, If, and Ig. Interior of dorsal valves, showing variation in position of the central and anterior lateral muscle 
 
 scars. University of Toronto, Canada. 
 Ih. Dorsal valve longitudinally compressed, giving it a very broad form. This may he compared with figures 
 
 Ic and If of Plate XXXVII. University of Toronto, Canada. 
 2. Cast of interior of a ventral valve, broadened by compression. University of Toronto, Canada. Specimen 
 
 figured by Matthew [1902c, PI. I, fig. 4b] as Oholus iequiputeis. 
 2a. Cast of interior of a dorsal valve. University of Toronto, Canada. Specimen figured by Matthew [1902c, 
 
 PI. I, fig. 4d] as Obolus a:quiputeis. 
 2b. Cast of the interior of a dorsal valve. University of Toronto, Canada. 
 
 The specimens represented are all from Locality 307d, Middle Cambrian sandy limestone of Division E2a? on Youngs 
 
 Point, near George River Station, Cape Breton, Nova Scotia. 
 
 LiNGULELL.v t'pi.s (Walcott) (p. .538). 
 
 Figures 3 and 3'. Top and side views of partly exfoliated ventral valve, the type specimen, from Locality 14i, Upper 
 Cambrian limestone 1 mile west of Cherokee, San Saba County, Texas. U. S. Nat. Mus. Cat. JIo. 
 51804a. 
 3a. Fragmentary dorsal valve associated with the ventral \al\-e represented by figure 3. U. S. Nat. Mus. 
 Cat. No. 51S04b. 
 
 LlXGUI>KI.LA BELL.V (Walcott) fp. 4.S1). 
 
 |1>1. XIX, figs. 2. 2a-(i.] 
 
 Figure 4. Slab of arenaceous shale with numerous well-preserved shells from Locality H4b, Lower Ordnvician sand- 
 stone 1 mile north of Lance Cove, Great Belle Island, Conception IJay, Newfoundland. L'. S. Mat. 
 Mus. Cat. No. 2730Sn. 
 124 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XXXVI 
 
 ' < .''X^J __.ji'^ 
 
 t^RANCES W>ESER DEL. 
 
 BLioTVPC :c eo 
 
PLATE XXXVII. 
 
 125 
 
PLATE XXXVII. 
 
 c. Trapezoidal area, including central, p. Pedicle groove. 
 
 middle lateral, and outside lateral ps. Parietal band. 
 
 muscle scars. s. Median septum. 
 
 g. TJmbonal muscle scar. v. Visceral cavity. 
 
 h. Central muscle scar. vs. Main va.scular sinus, 
 
 i. Transmedian muscle scar. ivs. Lateral branches of the vascular sj'.stein. 
 
 j. .\nterior lat;'ral muscle scar. x. Heart-shaped cavity. 
 1. Outside lateral muscle scar. 
 
 Obolus selwyni (Mattliew) (p. 41.3). 
 
 [PI. XXXVI, figs. 1. la-h, 2, L'a-b.] 
 
 Figure 1. Exterior of a distorted ventral valvo. University of Toronto, Canada. Possibly one of the specimens used 
 by Matthew in preparing the diagrammatic figures mentioned under figure Ic. 
 
 la. Cast of an interior of a ventral valve. University of Toronto, Canada. 
 
 lb. Cast of an interior of a ventral valve that has been compressed laterally. Univetsity of Toronto, Canada. 
 Possibly one of the specimens used by Matthew in preparing the diagrammatic figures mentioned 
 under figure Ic. 
 
 Ic. Cast of an interior of a dorsal valve. University of Toronto, Canada. Redrawn from the specimen upon 
 which Matthew [1903] based the diagrammatic figures in the right-hand figure on page 117 and in 
 figure lb of Plate VII of his paper. It may be taken as the type. 
 
 Id. Finely preserved interior of a ventral valve. University of Toronto, Canada. Possibly one of the speci- 
 mens used by Matthew in preparing th e diagrammatic figures mentioned under figure Ic. 
 
 le. Interior of the posterior portion of a dorsal valve. University of Toronto, Canada. 
 
 If. Cast of an interior of a dorsal valve. University of Toronto, Canada. Possibly one of the specimens used 
 by Matthew in preparing the diagrammatic figures mentioned under figure le. 
 
 The specimens represented are all from Locality 307d, Middle Cambrian sandy limestone of Divi.-ion E2a? on 
 Youngs Point, near George River Station, Cape Breton, Nova Scotia. 
 
 LiNGULELLA (LiNGULEPis) STARRi (Matthew) (p. 5.59). 
 
 Figure 2. Poorly preserved ventral valve. University of Toronto, Canada. 
 
 2a. Dorsal valve preserving a portion of the shell. University of Toronto, Canada. 
 2b. Cast of a portion nf the interior of a ventral valve. T'niversity of Toronto, Canada. 
 
 The specimens represented are all from Lmalit y 308c, Upp< r < 'ambrian shales of Matthew's Johannian at St. John, 
 New Brunswick. According to Matthew the type .specimens have been <ilh( r miflaid (<i lost. -Ml the fifrurr.s are 
 drawn from new material collected by him at the type locality. 
 
 LixGULELLA MixoR (Matthtnv) (p. .510). 
 
 Figure 3. Cast of the exterior id' a ventral valve slightly compres.sed and distorted in the .shale. University of Toronto, 
 
 Canada. Type specimen, figured by Matthew [1892, PI. XII, fig. .5a] as LingnleUa starri minor. 
 3a. Dorsal valve from which nearly all of the shell is exfoliated. University of Toronto, Canada. Specimen 
 
 figured by Matthew [1892, PI. XII, fig. 5b] as Lingulella starri viinor. 
 3b. Enlargement of the outer surface of the shell. University of Toronto, Canada. 
 3c. Ventral valve from siliceous -shale. U. S. Nat. Mus. Cat. No. 517(i.5a. 
 3d and 3e. Small ventral and dorsal valves from a fine arenaceous shale. U. S. Nat. Mus. Cat. Xos. 51765b 
 
 and 51765c, respectively. 
 3f and 3g. Small broad form of ventral and dorsal valves associated with narrower forms represented by figures 
 
 3d and 3e. V. S. Nat. Mus. Cat. Nos. 517G5d and 5I7G.5e, respectively. 
 
 The specimens are all frum Locality 2x, Upper Cambrian sandstones on Long Island, Kennebecasis Bay, St. John 
 County, New Brunswick. 
 126 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH U PL. XXXVII 
 
 t^RANCeS WtESER OEl. 
 
 MELIOTVPC CO eCSTOH 
 
PLATE XXXVII. 127 
 
 LiNGULELLA ROTUNDA (Mattliew) (]). 530, 
 
 Figure 3h. Exterior of a small ventral valve. U. S. Nat. Mus. Cat. No. 51770a. 
 3i. Cast of interior of ventral valve. U. S. Nat. Mus. Cat. No. 51770b. 
 3j and 3k. Casts of interior of dorsal valves. U. S. Nat. Mus. Cat. Nos. 51770c and 51770d. 
 
 The specimens represented are all from Locality 3i, Middle Cambrian sandy shale on McLean Brook, 1,5 miles west 
 of Marion Bridge, Cape Breton, Nova Scotia. 
 
 LiNGULELLA (LiNGXJLEPis) ROBERTi (Matthew) (p. 557). 
 
 Figure 4. Ventral valve preserving a portion of the outer surface. University of Toronto, Canada. 
 
 4a. Cast of the interior of a ventral valve, the type specimen. University of Toronto, Canada. (See note 
 
 following 4d.) 
 4b. Cast of the interior of a dorsal valve, preser\-ing outline and convexity of val\-e and impressions of muscle 
 
 scars. University of Toronto, Canada. (See note following 4d.) 
 4c. Enlargement of a portion of the outer surface of the antericir portion of a dorsal valve. University of 
 
 Toronto, Canada. 
 4d. Dorsal valve distorted by compre.ssion. University of Toronto, Canada. 
 
 The figures are all drawn from specimens in Matthew's type material. It is possible that the specimens represented 
 by figures 4a and 4b are the ones figured by Matthew [1895b, PI. I, figs. 2a and 2b, respectively], but closer identification 
 is impossible. The specimens represented are all from Locality 307d, Jliddle Cambrian sandy limestone of Division 
 E2a? at Youngs Point, near George River Station, Cape Breton, Nova Scotia. 
 
PLATE XXXVIII. 
 
 62667°— VOL 51, PT 2— 12 9 129 
 
PLATE XXXVIII. 
 
 a. Central lateral space of area. s. Median septum, 
 
 a'. Outer lateral space of area. v. Visceral cavity, 
 
 f. Fle-xure line of area. vs. Main vascular sinus, 
 
 h. Central muscle .scar. ivs. Lateral branches of the vascular system. 
 
 , j. Transmedian muscle scar. pvs. Periplieral branches of the vascular system. 
 
 p. Pedicle groove. x. Heart-shaped cavity. 
 
 LiNGULELLA MARTINENSIS MattlieW (p. 51 S^. 
 
 Figure 1. E.xterior of an unusually well-prcsorved ventral valve. University of Toronto, Canada, Drawn from 
 a specimen in Matthew's type and fi},'ured material, but closer identification is impossible, 
 la. Cast of the interior of a ventral valve. University of Toronto, Canada. Type specimen figured by 
 
 Matthew [1895a, PI. II, fig. 6d]. 
 lb. Interior of a ventral valve from which nearly all of the inner layers of the shell have been exfoliated. 
 University of Toronto, Canada. Drawn from a specimen in Matthew's type and figured material, but 
 closer identification is impossible. 
 Ic. Interior of a dorsal valve. University of Toronto, Canada. Drawn from a specimen in Matthew's typeand 
 
 figured material, but closer identification is impossible. 
 Id. Cast of the interior of a dorsal valve. University of Toronto, Canada. Specimen figured by Matthew 
 
 [189.5a, PI. II, fig. 6b]. 
 le. Enlargement of the area of the specimen represented by figure id. 
 The specimens represented by figures 1, la-e are from Locality 2f, Middle Cambrian sandstones of Division Ibl, 
 on Ilanford Brook, St. John County, New Brunswick. 
 
 Figures If and Ig. Ventral and dorsal valves which occur in the collection of the University of Toronto, Canada, 
 labeled by Matthew as Linguldla dciwsoni from Division Ic of the St. John slate. They appear 
 to be more nearly related to LinguleUa martinensis. They may or may not be the specimena 
 illustrated by Matthew [1880, PI. V, figs. 9, 9a-c]. 
 
 LiNGULELLA GRANDIS (Mattliew) (p. 50"2). 
 
 Figure 2. Partly exfoliated dorsal valve. University of Toronto, Canada. 
 
 2a. Cast of the interior of the posterior portion of a ventral valve. University of Toronto, Canada. 
 Figures 2 and 2a (with 2c and 2d ) are drawn from specimens in Matthew's type material of LinguleUa f cuneata, but 
 it is impossible to tell which of these he figured [1894, PL XA'I, figs. .5a-b]. 
 
 Figure 2b. Slightly imperfect cast showing the greater part of the interior of a ventral valve. University of 
 Toronto, Canada. Type specimen, figured by Matthew [1894, PL XVI, fig. 7a] as Leptobolus grandis. 
 2c. Cast of the interior of a ventral valve. University of Toronto, Canada. 
 2d. Cast of the interior of a dorsal valve. University of Toronto, Canada. 
 Figures 2c and 2d (with 2 and 2a) are drawn from specimens in Matthew's type material of LingukUa f cuneata, but 
 it is impossible to tell which of these he figured [1894, PL XVI, figs. 5a-b]. 
 
 Figure 2e. Posterior portion of a dorsal valve, showing cast of the area. L'niversity of Toronto, Canada. Labeled 
 by Matthew as Leptobolus grandis. 
 2f. Part of the interior of a dorsal valve. University of Toronto, Canada. Specimen figured by Matthew 
 [1894, PL XVI, fig. 7b] as Leptobolus grandis. 
 The specimens represented by figures 2, 2a-f are all from Locality 30Is, Lower Ordovician sandstone at McAphee's 
 Comer, Hardingville, St. John County, New Brunswick. 
 
 Obolus belli (Billintrs) (p. 386). 
 
 Figures 3 and 3a. Ventral valves from Locality 319n, Ordovician, on the island of Montreal. Canada. Geol. Survey 
 Canada. Redrawn from the specimens figured by Billings [18.59, pp. 431-432, figs. 7 and 8], but closer 
 identification is impossible. Figure 3 may be taken as the type. 
 3b. Dorsal valve associated with the specimens represented by figures 3 and 3a. Geol. Survey Canada. 
 
 LiNGULELLA WELLERI (Walcott) (p. 539). 
 
 Figure 4. Compressed and somewhat crushed ventral valve, the type specimen, showing only the general outline 
 and the outer surface. V. S. Nat. Mus. Cat. No. 35292a. 
 4a. Apex and posterior portion of the ventral valve, preserving the convexity. U. S. Nat. Mus. Cat. No. 
 
 35292b. 
 4b. A compressed dorsal valve. U. S. Nal. Mu.«. <'at. No. 35292c. 
 The specimens represented are all from Locality lie, Upper Cambrian sandstone, O'Donnell and McManniman's 
 quarry, Newton, New Jersey. 
 130 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XXXVIII 
 
 / 
 
 J^^<. 
 
 Z" 
 
 HELIOTYPE CO.. BOSTON 
 
PLATE XXXIX. 
 
 131 
 
PLATE XXXIX. 
 
 a. Central lateral space of area, 
 
 a'. Outer lateral space of area. 
 
 f. Flexure line of area, 
 
 h. Central muscle scar, 
 
 i. Transmedian muscle scar, 
 
 j. Anterior lateral muscle scar. 
 
 1. Outside lateral and middle lateral muscle 
 
 scars on dorsal valve, 
 p. Pedicle groove, 
 s. Median septum. 
 V. Visceral cavity, 
 vs. Main vascular sinus. 
 
 LiNGULELLA WANNiECKi RedUch (p. 538). 
 
 Figure 1. Elongate form of the ventral valve. U. S. Nat. Mils. Vat. No. 51744o. 
 
 la, lb, and Ic. Short, broad, subtriangular forms of the ventral valve. U. S. Nat. Mus. Cat. Nos. 51744a, 
 
 5i744b, and 51744(", respectively. 
 Id. Cast of the interior of a ventral valve, showing the area, visceral area, and \asciilar sinuses. U. S. Nat, 
 
 Mus. Cat. No. 51744d. 
 le. Imperfect interior of a ventral valve. U. S. Nat. Mus. Cat. No. 51744e. 
 If. Dorsal valve in position against the ventral valve, showing the area of the ventral valve. U. S. Nat. Mus. 
 
 Cat. No. 51744f. 
 Ig, Ih, and li. Exteriors of dorsal valves, varying somewhat in outline. U. S. Nat. Mus. Cat. Nos. 51744g, 
 
 51744h, and 51744i, respectively. 
 Ij and Ik. Interiors of imperfect dorsal valves. U. S. Nat. Mus. Cat. Nos. 51744J and 51744k, respectively. 
 1 1. Interior of a remarkably well preserved dorsal valve. U. S. Nat. Mus. Cat. No. 51744 1. 
 Im. Cast of the interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 51744m. 
 In. Interior of a dorsal valve, showing anterior lateral scars and narrow ridges in the position of the main 
 
 vascular sinuses. U. S. Nat. Mus. Cat. No. 51744n. 
 
 The specimens represented are all from Locality 15r, Middle Cambrian argillaceous shale at Khussak, Salt Range, 
 India. 
 
 LiNGULELLA FiiCiisi ReclHch (p. 502). 
 
 FiGUKE 2. Narrow elongate form which may be compared with figure 3. U. S. Nat. Mus. Cat. No. 51746a. 
 2a. Cast of a very small dorsal valve. U. S. Nat. Mus. Cat. No. 51746b. 
 
 2b and 2c. Dorsal valves referred to this species. U. S. Nat. Mus. Cat. Nos. 51746c and 51746d, respectively. 
 3. Ventral valve, the type specimen. Copied from Redlich [1899, PI. I, fig. 10c]. 
 
 The specimens represented are all from Locality 15r, Middle Cambrian argillaceous shale at Khussak, Salt Range, 
 India. 
 
 LiNGULELLA issE (Walcott) (p. 509). 
 
 [Text figs. 4:iA-F, p. 5I0.I 
 
 Figures 4 and 4a. Narrow and broad forms of ventral valves, with e.xterior shell partly exfoliated. U. S. Nat. Mus. 
 Cat. Nos. 51808a and 51808b, respectively. Figure 4a represents the type specimen. 
 4a'. Side outline of specimen represented by figure 4a. 
 4b and 4b'. Exfoliated dorsal valve and side outline. U. S. Nat. Mus. Cat. No. 51808c. 
 
 The specimens represented are all from Localil>' 15d, ITpper Cambrian limestone near Cave Spring, Fish Spring 
 Range, Utah. 
 
 Obolits mcconnelli pelia.s (Walcott) (p. 398). 
 
 [PI. XXIII, figs. Sb-c.] 
 
 Figure 5. Ventral valve with outer layer of shell exfoliated, from Locality 15p, Middle Cambrian limestones near the 
 north end of the Fish Spring Range, Utah. U. S. Nat. Mus. Cat. No. 51597a. 
 5a and 5b. Partly exfoliated dorsal valves as.sociated with the specimen repre.senled by figure 6. U. S. 
 
 Nat. Mus. Cat. Nos. 51597b and 51597c, respectively. 
 5c. A dorsal valve doubtfully referred to this species, from Locality 7s, Upper Cambrian shale 4 miles south- 
 southeast of Emigrant Peak, Silver Peak quadrangle, Nevada. U. S. Nat. Mus. Cat. No. 51593a. 
 132 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XXXIX 
 
 MELIOTYPE CO.. BOSTON, 
 
PLATE XXXIX. 133 
 
 LiNGULELLA QUADRILATERALIS (Walcott) (p. 528). 
 
 Figure G. Ventral valve with outer layer of shell exfoliated, the type Bpecimen, from I-ocality 91, Middle < aiiilirian 
 shales at Cedar Bluff, Cherokee County, Alabama. U. S. Nat. Mus. Cat. No. 51777a. 
 Ga. I>ursal valve and side outline of united valves, associated with the specimen represented by figure 6. 
 U. S. Nat. Mus. Cat. No. 51777b. 
 
 Obolus chinensis (Walcott) (p. 387). 
 
 Figure 7. Partly exfoliated ventral valve, the type specimen. U. S. Nat. Mus. Cat. No. 52532a. 
 
 7a. Interior of a ventral valve. U. S. Nat. Mus. Cat. No. 52532b. Another specimen (Cat. No. 52532c) was- 
 
 used to restore certain parts of this drawing. 
 7b. Exfoliated dorsal valve, showing visceral area. U. S. Nat. Mus. Cat. No. 52532d. 
 
 The specimens represented are all from Locality C62, Middle Cambrian limestones 2.5 miles south of Yenchuang, 
 Sintai district. Shantung, China. 
 
 LiNGULELLA DAMESI (Walc'Ott) (]). 489). « 
 
 Figure 8. Top and side view of a partly exfoliated ventral valve, showing outline of posterior portion of visceral 
 area and position of the main vascular sinuses. U. S. Nat. Mus. Cat. No. 52529a. 
 8a. Partly exfoliated ventral valve, the type siiecimen. U. S. Nat. Mus. Cat. No. 52529b. 
 8b. Exterior of a ventral ? valve. U. S. Nat. Mus. Cat. No. 52529c. 
 8c. Partly exfoliated dorsal valve. U. S. Nat. Mus. Cat. No. 52529d. 
 
 The specimens represented are all from Locality CIO, Middle Cambrian limestone about 3 miles southwest of 
 Yenchuang, Sintai district, Shantung, China. 
 
 LiNGULELLA (LiNGULEPIs) EROS (Walcott) (p. 551). 
 
 Figures 9 and 9a. Ventral and dorsal valves restored in outline from other specimens. Locality C7, Middle Cambrian 
 limestone 2.2 miles southwest of Yenchuang, Sintai district. Shantung, China. U. S. Nat. Mus. 
 Cat. Nos. 52527a and 52527b, respectively. Figure 9 represents the type specimen, 
 
 Obolus (Westonia) blackwelderi Walcott (p. 453). 
 
 Figure 10. An elongate ventral valve, the type specimen, with posterior portion broken away, from Locality C6, 
 
 Middle Cambrian shaly limestone 2.5 miles southwest of Yenchuang, Sintai district. Shantung, 
 
 China. U. S. Nat. Mus. Cat. No. 52540a. 
 10a. Short form of ventral valve as.sociated with the shell represented by figure 10. U. S. Nat. Mus. Cat. No. 
 
 52540b. 
 10b. Exterior of a dorsal valve from Locality C2, Middle Cambrian limestone 2 miles south of Yenchuang, 
 
 Sintai district. Shantung, China. IT. S. Nat. Mus. Cat. No. 52541a. 
 10c. Enlargement of surface of a shell associated with the ventral valve represented by figure 10. L'. S. Nat. 
 
 Mus. Cat. No. 52.540c. 
 
 LiNGULELLA HEBERTI BaiTois (p. 505). 
 
 11. Exterior of ventral valve. 
 
 11a. Exterior of dorsal valve. 
 
 lib. Cast of interior of ventral valve, the type specimen. 
 
 lie. Enlargement of the outer surface. 
 
 Figures 11, lla-c are copied from Barrois [1882, PI. IV, figs. 3a-d, respectively]. The specimens represented 
 are all from Locality 350a, Ordovician sandstone at Cape Vidio, Province of Oviedo, Spain. 
 
 u Now referred to Obolus ; see p. 489. 
 
PLATE XL. 
 
 135 
 
PLATE XL. 
 
 V. Visceral cavity. 
 
 LiNGULELLA (LiNGULEPIS) ACUMINATA (Conrad) (p. 545). 
 
 [PI. XXXIV, figs. 3, 3a-e; Pi. XLI, figs. 1, la-n; and PI. XLII, fljs. 1, la o.) 
 
 Figure 1. Ventral valves, the type specimens, from Locality 338s, Upper Cambrian sandstone at High Bridge on 
 Ausable River, Essex County, New York. Copied from Hall [1847, text fig., p. 9], who states that the 
 figure is copied from a drawing made by Conrad, 
 la. Ventral valves from Locality 338s, llpper Cambrian sandstone at High IJridge on Ausable River, Essex 
 
 County, New York. Copied from Emmons's figure [1842, text fig. 68, p. 2G8] of Lingula anliqua. 
 lb. Partly exfoliated ventral valve, showing the visceral cavity, from Locality 110, Upper Cambrian sand- 
 stone, east side of the town of Whitehall, New York. U. S. Nat. Mus. Cat. No. 51877a. 
 Ic. Narrow ventral valve associated on the same slab of rock with figure lb. U. S. Nat. Mus. Cat. No. 51877b. 
 Id and le. Dorsal valves associated with the ventral valves represented by figures lb and Ic. U. S. Nat. 
 
 Mus. Cat. Nos. 51877c and 51877d, respectively. 
 If and Ig. Small ventral and dorsal valves, from Locality 109, Upper Cambrian sandstone 1.5 miles south of 
 
 Deweys Bridge on the Champlain Canal, Washington County, New York. U. S. Nat. Mus. Cat. 
 
 Nos. 51879a and 51879b, respectively. 
 Ih. Ventral valve from Locality 76a, Upper Cambrian arenaceous limestone 1 mile north of Saratoga Springs, 
 
 New York. U. S. Nat. Mus. Cat. No. 52469a. 
 li, Ij, and Ik. Ventral valves, from Locality 76, Upper Cambrian impure limestones 4 miles west of Saratoga 
 
 Springs, New York. U. S. Nat. Mus. Cat. Nos. 51S78a, 51878b, and 51878c, respectively. 
 1 1, Im, and In. Dorsal valves associated with the specimens represented by figures li, Ij, and Ik. I'. S. 
 
 Nat. Mus. Cat. Nos. 51878d, 51878e, and 51878f, respectively, 
 lo. A broad ventral valve, from Locality 392, Upper Cambrian Potsdam sandstone. Burgess, Canada. U. S. 
 
 Nat. Mus. Cat. No. 17999a. 
 Ip and Iq. Narrow and broad form of the ventral valve, from Locality 105, Upper Cambrian limestone at 
 
 Bishops Mill, Hancock County, Tennessee. U. S. Nat. Mus. Cat. Nos. 51881a and 51881b, 
 
 respectively. 
 Ir and Is. Dorsal valves associated with the ventral valves represented by figures Ip and Iq. U. S. Nat. 
 
 Mus. Cat. Nos. 51881c and 51881d, respectively. 
 136 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XL 
 
 FRANCES WieSER DEL. 
 
 MCL10T*Pe CO I 
 
PLATE XLI. 
 
 137 
 
PLATE XLI. 
 
 k'. Outer lateral space of area. p. Pedicle groove, 
 
 h. Central muscle scar. v. \'i5ceral cavity. 
 
 J. .\nterior lateral muscle scar. vs. Main vascular si[iu5. 
 
 LiNGULELLA (LiNGULEPis) ACUMINATA (Conrad) (p. 545). 
 
 [PI. XXXIV, figs. 3, 3a-e; PI. XL, figs. 1, la-s; and I'l. XLII, figs. 1, la-o.] 
 
 Figure 1. Slab figured by Owon [1852, PI. IB, fig. 8] as Lingula plnnaformis. U. S. Nat. Mus. Cat. No. 17860a. 
 
 Locality 328h, Upper Cambrian sandstone at the falls of the St. Croix, Polk County, Wisconsin, 
 la, lb, and Ic. Partly exfoliated ventral valves, sho\ring more or less of the area and interior vascular 
 
 markings. These occur in Locality 82s, Upper Cambrian sandstone at St. Croix Falls, Wisconsin. 
 
 U. S. Nat. Mus. Cat. Nos. 51888a, 51888b, and 51888c, respectively. 
 Id and le. Ventral valves associated ivith the shells represented by figs. la-c. L'. S. Nat. Mus. Cat. No3. 
 
 51888d and 51888e, respectively. 
 If. Dorsal valve associated with specimen represented by figure la. U. S. Nat. Mus. Cat. No. 51888f. 
 Ig. Dorsal valve associated with the specimen represented by figure la, showing the area and the central 
 
 muscle scars. U. S. Nat. Mus. Cat. No. 51888g. 
 Ih. Exfoliated dorsal valve associated with specimen represented by figure la. U. S. Nat. Mus. Cat. No. 
 
 51888h. 
 li. Ventral valve, from Locality 79b, Upper Cambrian sandstone near Hudson, St. Croix County, Wisconsin. 
 
 U. S. Nat. Mus. Cat. No. 51889a. 
 Ij, Ik, and 1 1. Exfoliated dorsal valves associated with the ventral valve reprgsented by figure la. U. S. 
 
 Nat. Mus. Cat. Nos. 518881, 51888J, and 51888k, respectively. 
 Im. Dorsal valve associated with the specimen represented by figure li. U. S. Nat. Mus. Cat. No. 51889b. 
 In. Small exfoliated ventral valve, from Locality 84, Middle Cambrian sandstone at Dresbach, Winona County, 
 
 Minnesota. U. S. Nat. Mus. Cat. No. 51885a. 
 
 LiNGULELLA (LiNGULEPIs) ACUMINATA MEEKI (Walcott) (p. 550). 
 
 Figures 2 and 2a. Ventral and dorsal valves fnun Locality 302b, Middle Cambrian limstone near Crowfoot Ridge 
 Yellowstone National Park, Wyoming. U. S. Nat. Mus. Cat. Nos. 35206a and 35206b, respectively. 
 Figure 2 represents the type specimen. 
 138 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XLI 
 
 =;*ANCE8 WIESER DEL. 
 
 HEUOTVPE CO.. BOSTON. 
 
PLATE XLII. 
 
 139 
 
PLATE XLII. 
 
 a. Central lateral space of area, 
 a'. Outer lateral space of area. 
 c. Trapezoidal area, including central, middle 
 
 lateral, and outside lateral muscle scars, 
 g. ITmbonal muscle scar. 
 
 h. Central mu.scle scar. 
 j. Anterior lateral muscle scar, 
 p. Pedicle groove. 
 V. Visceral cavity, 
 vs. Main vascular sinus. 
 
 LiNGULELLA (LiNGULEPIs) ACUMINATA (C'oniad) (p. 545). 
 
 |I1. XXXIV, figs. 3. 3a-e; PI. XI,. figs. 1, la-s: and IM. XLI. 
 
 . 1. la-n.] 
 
 FiGUBES 1 and Id. Narrow, oxfciliated ventral valve .showing the visceral area. The .-^ide view, figure Id, shows the 
 
 outline of the area and the cast of the pedicle groove. Locality 355, Middle Cambrian sandstones on 
 
 Red Canyon Creek, Black Hills, South Dakota. U. S. Nat. Mus. Cat. No. 51894a. 
 la and lb. Broad ventral and dorsal valves, identified by WTiitfield as LinguUpis pinnaformis. Locality 355, 
 
 Middle Cambrian sandstones on Red Canyon Creek, Black Hills, South Dakota. U. S. Nat. Mus. 
 
 Cat. Nos. 24588a and 2458Sb, respectively. 
 Ic. Dorsal valve retaining a considerable amount of ihe laminated portion of the shell. From Locality 355d, 
 
 Upper Cambrian friable reddi.sh sandstone. Black Hills, South Dakota. U. S. Nat. Mus. Cat. No. 51898a. 
 le. Cast of the interior of a ventral valve associated with the shell represented by fig. Ic, showing area, pedicle 
 
 groove, and vascular markings. U. S. Nat. Mus. Cat. No. 51S98b. Another specimen (Cat. No. 
 
 51898c) was used to aid in restoring this figure. 
 If. Cast of the interior of a broad dorsal valve, from the friable purple sandstones of Locality 355b, Jliddle 
 
 Cambrian, on Castle Creek, Black Hills, South Dakota. IT. S. Nat. Mus. Cat. No. 1026b. 
 Ig and Ih. Casts of the interior of broad ventral and dorsal valves. From Locality 355d, Upper Cambrian 
 
 sandstone. Black Hills, South Dakota. U. S. Nat. Mus. Cat. Nos. 51898d and 51S98e, respectively. 
 li and Ij. Young shells that occur in abundance in the same layers with the specimens represented by figures 
 
 Ig and Ih. L". S. Nat. Mus. Cat. Nos. 51899a and 51899b, respectively. 
 Ik, 11, and Im. Ventral valves from Locality 70, Upper Cambrian limestones on Morgans Creek, Burnet 
 
 County, Texas. U. S. Nat. Mus. Cat. Nos. 51891a, 51891d, and 51891b, respectively. 
 In. Dorsal valve associated with the ventral valves represented by figures Ik, 11, and Im. V . S. Nat. 
 
 Mus. Cat. No. 51891c. 
 lo. Cast of interior of dorsal valve, showing position of central and lateral muscle scars. From Locality 14b, 
 
 Upper Cambrian limestone on Cold Creek, Llano County, Texas. XJ. S. Nat. Mus. Cat. No. 51892a. 
 
 Obolus (Westonia) rogeksi (Walcott) (p. 463). 
 
 Figure 2. Partly exfoliated ventral valve, the type specimen, illustrating the different layers forming the shell. 
 
 U. S. Nat. Mus. Cat. No. 27336a. 
 2a. Cast of the interior of a ventral valve, showing the area and vascular markings. U. S. Nat. Mu.s. Cat. No. 
 
 27336b. 
 2b. Cast of the interior of a ventral valve in which the area extends far down the cardinal slopes. L'. S. Nat. 
 
 Mus. Cat. No. 27336c. 
 2c. Cast of the interior of a dorsal valve, showing the central position of the central muscle scars. U. S. Nat. 
 
 Mus. Cat. No. 27336d. 
 2d. Partly exfoliated dorsal valve on which a i)or(ion of the surface of the outer shell is preserved. L^. S. 
 
 Nat. Mus. Cat. No. 27336e. 
 
 The specimens represented are all from Locality 343, Lower Ordovirian limestone pebbles on the beach near New- 
 port, Rhode Island. 
 
 Obolus (Lingulobolus) spissus (Billings) (p. 432). 
 
 [II. XVI, figs. 2. 2a-k.] 
 
 Figure 3. Enlargement of the surface of the specimen representcil by Plate X\ I, figure 2b, of this monograph. U. S. 
 Nat. Mus. Cat. No. 51678b. 
 3a. Enlargement of the outer surface of the inner layer in front of iho umbonal muscle scar, of the dorsal valve 
 represented by Plate XVI, figure 2, of this monograph. U. S. Nat. Mtis. Cat. No. 51678 1. 
 
 The specimens represented are both from Locality 114b, Upper Cambrian sandstone, 1 mile north of Lance Cove, 
 Great Belle Island, Conception Bay, Newfoundland. 
 140 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL.XLII 
 
 J_ 
 
 A 
 
 2" 
 
 sg^^ps^ 
 
 FRANCES WIESEK DEL 
 
 HELIOTVPE CO., BOSTON 
 
PLATE XLIII. 
 
 141 
 
PLATE XLIII. 
 
 a. Central lateral space of area, 
 a'. Outer lateral space of area, 
 c. Trapezoidal area, iiHliidlng central, iiiWdle 
 
 lateral, and outsiile lateral muscle scars. 
 f. Flexure line of area. 
 
 h. Central muscle scar, 
 j. -\nterior lateral muscle scar, 
 p. Pedicrle groove. 
 vs. Main vascular sinus. 
 X. Heart-shaped cavity. 
 
 If. 
 
 Ig. 
 Ih. 
 li. 
 
 LiNGULELLA (LiNGULEPIs) EXIGUA (Matthcw) (p. 551). 
 [PI. X.XXin.ligs. 4 and 4a.) 
 
 FiGUR. 1. Narrow acuminata ventral valve from Locality lot, Middle Cambrian sandstone on McLean Brook near 
 Marion Bridge, Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. No. 347G6a i^rook, near 
 
 ' S'm^^cS™ ;? S^: '-'-' ''- '''' -'--'^-" '^y '"^^- '' ^"' --'-^^ ^-^^ - U. S. 
 
 lb. Broader form of ventral valve than that represented by figure la, but a,ssociated with it Specimens 
 V """.T-f^f *'°"' "^ ^""" ^°'^^'^° '^"""'^ 1^ ^"^' ^^ "'-'■"^ ^^ 'he collections. U. S. Nat. Mus. Cat 
 
 Ic. still broader form of ventral valve intermediate between specimens represented by figures lb and If 
 Associated with the specimens represented by figures 1, la-b. U. S. Nat. Mus. Cat No 34766e 
 
 Id. S-al V , ,,th slightly roun.led instead of straight or incurved cardinal slopes, from I ocaHty 
 
 3 , Mid<Ile Cambrian ^ndstone on McLean Brook, l.r, miles west of Marion Bridge, Cape Breton 
 Nova Scotia. U. S. Nat. Mus. Cat. No. 34761a g . "^"^pe creion, 
 
 ^'''" Na^'t^Mus^CaJ^No'' "'"'"'' ^'''"'' associated with the specimen represented by figure Id. U. S. 
 Elongate and attenuate ventral valve, showing cast of the interior surface, also a portion of the outer 
 surface. It is associated with the shell represented in figure Id. U. S. Nat. Mus Cat No 34761d 
 
 ngureld. U. S. Nat. Mus. Cat. No. 34761e. 
 
 '^'"'''wftrtlf "l^T""^ ventral valve compressed and flattened in the arenaceous shale. It is associated 
 with the shell represented in figure Id. U. S. Nat. Mus. Cat No 34761f 
 Ij. Cast of interior of a broad form of ventral valve somewhat like specimen represented by figure 2c in outline 
 1 1 Sn, 1 ' "T"' "■' u'^' specimens represented by figures 1, la-c. U. S. Nat. Mus Cat. No 34766d' 
 
 "'"'''^::Tti"^S^TZS;^'''-'- — ^^-dwith.heshellrepresented 
 
 m. Fragment of arenaceous shale from Locality lOt (see fig. 1, above), with a group of small shells upon it 
 
 Natural size. U. S. Nat. Mus. Cat. No. 34766f ^ 
 
 lo. Cast ;'f the interior of ventral valve showing cast of pits and the strong ridges of the main vascular canals, 
 
 from J-"caIity 31. Middle Cambrian sandstone on McLean Brook, 1..5 miles west of Marion Bridge 
 
 tape Breton, Nova Scotia. V. S. Nat. Mus. Cat. No. 34761 j 
 Ip. Part of the interior of a ventral vah-e associated with the specimen represented by figure lo, showin<. the 
 
 strong ridges beneath the main va,srular ..inusos. U. S. Nat Mus Cat No .34761k 
 Iq. Cast of interior of a ventral valve, showing heart-shaped area (x), trapezoidal area (c), and cast of vascular 
 
 canal ridges (vs). locality 10s, Mid.lle Cambrian .xndstone on McLean Brook, near Marion BHd'e 
 
 tape Breton, Nova Scotia. U. S. Nat. Mus. Cat. No. 52468b 
 Ir. Cast of interior of a <Iors;,l valve associated «-ith the specimen represented bv figure Iq, showing area 
 
 visceral cavity, and portion of vascular canal ridges. U. S. Nat. Mus. Cat. No. 52468c \notber 
 
 1, Cast oTth "'"T ■ V ^- ''?"■; ^'■"'" ^°''^''y ^'^ '"^^ "^^ *° ^^'"'^ ^^^«*'" P^^'i"'^^ "f this figure. 
 
 of the interior o a dors.il va ve a.ssociated ^Wth the specimen represented by figure lo, showing strongly 
 marked visceral and vascular ridges. U. S. Nat. Mus. Cat. No 34761 1 " " ' ^ ^■ 
 
 142 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XLIII 
 
 i 
 
 .'■•/ 
 
 
 / 
 
 
 .A 
 
 
 -^ 
 
 y\ 
 
 • ■■ 'f^ .-'- 
 
 :h 
 
 / rr^W>-. 
 
 t 
 
 ■ i-^j% 
 
 
 y^,^\ 
 
 ■■' ^^'^-^^ 
 
 
 v'i? 
 
 
 
 '■■//■'-V 1 
 
 
 
 ' '^' .,' ' 
 
 '■':ii^^^ ' < 
 
 4% 
 
 
 y 
 
 >\ 
 
 ^ X't/^ 
 
 
 '''.■;jii'i''^ji'iU^' 
 
 
 
 f . 
 
 (^ 
 
 v\. 
 
 s.' f I '/ I •. 
 
 vA, ■yr^m^^''^i'¥' 
 
 lr\^ 
 
 A 
 
 9 
 
 Wm. 
 
 'M\k ' 
 
 FRANCES WIESER DEL. 
 
 LtOTVPE CO BCSTOM 
 
PLATE XLIII. 143 
 
 LiNGULELLA (LiNGULEPis) ExiGUA (Matthcw) — Continued. 
 
 Figure It. Large, partly exfoliated dorsal valve, of the same type as the ventral valve represented by figure 1. 
 
 Associated with the specimen represented by figure Iq. U. S. Nat. Mus. Cat. No. 52468d. 
 lu, Iw, and Ix. Casts of the interior of dorsal valves showing variation in outline, form of visceral cavity, 
 
 pitting of inner surface of valve, etc. Associated with the specimen represented by figure Iq. U. S. 
 
 Nat. Mus. Cat. Nos. 34761m, 34761o, and 34761p, respectively. 
 Iv. Interior of a dorsal valve associated with the specimen represented by figure Iq, in which the pits are 
 
 arranged like beads along the lines of growth. U. S. Nat. Mus. Cat. No. 347f)ln. 
 ly. Part of interior of dorsal valve associated with the specimen represented by figure Iq, showing ridges 
 
 on which the central muscle scars occur, main vascular canal ridges, and fine pitting of surface. U. S. 
 
 Nat. Mus. Cat. No. 34761q. 
 Iz. Cast of interior of dorsal valve in which the visceral area extends well toward the front. Locality llz, 
 
 Middle Cambrian sandstone on Big Ridge, 2 miles south of Marion Bridge, Cape Breton, Nova Scotia. 
 
 U. S. Nat. Mus. Cat. No. 51870a. 
 
PLATE XLIT 
 
 62667°— VOL 51, pt 2—12 10 145 
 
PLATE XLIV. 
 
 a. Central lateral space of area. p. Pedicle groove. 
 
 h. Central muscle scar. v. Visceral cavity. 
 
 LiNGULELLA (LiNGULEPis) GREGWA (Matthew) (p. 5.54). 
 
 Figure 1. Very perfect ventral valve preserving the entire exterior .«urfare, from Loealily lOp", Middle Cambrian 
 
 sandstones between Indian River and McPhees Brook, Cape Breton, Nova Scotia. U. S. Nat. Mus. 
 
 Cat. No. 51875a. 
 la. Cast of the interior of a ventral valve from Locality lOp, Middle Cambrian sandstones of Division E2b, 
 
 Dugald Brook, Cape Breton, Nova Scotia, showing the vascular sinuses. U. S. Nat. Mus. Cat. No. 
 
 51873a. 
 lb. Enlargement of a small ventral valve associated with the shell represented by figure la. U. S. Nat. Mus. 
 
 Cat. No. 51873b. 
 Ic. Elongate ventral valve from Locality lOp', Middle Cambrian sandstones on Gregwa Brook, Cape Breton, 
 
 Nova Scotia. U. S. Nat. Mus. Cat. No. 51874a. 
 Id. Partly exfoliated ventral valve a-ssociated with the shell represented by figure la. U. S. Nat. Mus. 
 
 Cat. No. 51873c. 
 le. Small ventral valve associated with the shell represented by figure Ic, showing the cast of a long pedicle 
 
 furrow and a portion of the area. U. S. Nat. Mus. Cat. No. 51874b. 
 If. Cast of the interior of a very broad ventral valve associated with the shell represented by figure 1, on which 
 
 a portion of the outer shell is preserved. U. S. Nat. Mus. Cat. No. 51875b. 
 Ig. Fragment of small ventral valve associated with the shell represelited by figure 1, showing the area and 
 
 the character of the outer surface of the shell. U. S. Nat. Mus. Cat. No. 51875c. 
 Ih. Cast of part of the interior of a small dorsal valve associated with the specimen represented by figure la. 
 
 U. S. Nat. Mus. Cat. No. 51873e. 
 • li. Small o\al dorsal valve associated with the specimen represented by figiu-e la. U. S. Nat. Mus. Cat. 
 
 No. 51873f. 
 Ij. Transversely oval dorsal valve, preserving the outer surface, associated with the specimen represented 
 
 by figure la. U.S.Nat.Mus. Cat. No. 51873g. The outer surface of this shell is enlarged in figure Ip. 
 Ik. Cast of the interior of a subtriangular dorsal valve, showing the -s-isceral area, associated with the shell 
 
 represented by figure la. U. S. Nat. Mus. Cat. No. 51873h. 
 11. Cast of the interi<ir of an elongate dorsal valve associated with the shell represented by figxire la. U. S. 
 
 Nat. Mus. Cat. No. 51873d. 
 Im. Cast of the interior of an elongate dorsal valve associated with the shell represented by figure Ic. U. S. 
 
 Nat. Mus. Cat. No. 51874c. 
 In. Cast of the interior of a dorsal valve associated with the shell represented by figure Ic. V. S. Nat. Mus. 
 
 Cat. No. 51874d. The concentric lines of tubercles have been drawn in from other specimens (Cat. 
 
 Nos. 518731 and 51873J from Locality lOp). 
 lo. Enlargement of a portion of surface of a very perfectly preserved dorsal valve 12 mm. in length from 
 
 Locality 13t", Middle Cambrian sandstones of Divisions Elc and Eld on Dugald Brook, Cape Breton, 
 
 Nova Scotia. V. S. Nat. Mus. Cat. No. 56792a. 
 Ip. Enlargement of the surface of the dorsal valve represented in figure Ij to t^how the irregular, concentric, 
 
 undulating ridges. V. S. Nat. Mus. Cat. No. 51873g. 
 
 LiNGULELLA (LiNGTJLEPis) LONGiNERVis (Matthew) (p. 555). 
 
 Figures 2 and 2a. Exteriors of two small ventral valves, with nearly straight cardinal margins. Locality 13p, Middle 
 
 Cambrian sandstones 40 feet above Di^•ision E2a on Dugald Brook, Cape Breton, Nova Scotia. U. S. 
 
 Nat. Mus. Cat. Nos. 51872a and 51872b, respectively. 
 2b. Partly exfoliated ventral valve, with incurved cardinal margins. Locality 13g, Middle Cambrian 
 
 sandstones 10 feet above Division E2a, Dugald Brook, Cape Breton, Nova Scotia. U. S. Nat. Mus. 
 
 Cat. No. 56977a. 
 2c. Interior of a broken ventral valve, showing visceral cavity, area of central muscle scars, etc. Locality 
 
 13f, Middle Cambrian sandstones 20 feet above Division E2a, Dugald Brook, Cape Breton, Nova 
 
 Scotia. U. S. Nat. Mus. Cat. No. 56974a. 
 2d. Exterior of a dorsal valve from Locality lOp, Middle Cambrian sandstones of Di\'ision E2b, on Dugald 
 
 Brook, Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. No. 34764a. 
 2e. Interior of a dorsal valve from Locality 344o, Middle Cambrian sandstones of Division E2b, on Dugald 
 
 Brook, Cape Breton, Nova Scotia. Univer.'^ily of Toronto, < inada. Specimen figured by Matthew 
 
 [1903, PI. VII, fig. 6f]. The two figures should be compared. 
 2f and 2g. Casts of j>arts of interiors of dorsal valves, .showing position of central scars. Locality 13d, Middle 
 
 Cambrian sandstones between Divisions E2a and E2b, Dugald Brook, Cape Breton, Nova Scotia. 
 
 r. S. Nat. Mus. Cat. Nos. 56976a and 56976b, respectively. 
 146 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XLIV 
 
 FRANCES WIE8ER DEL 
 
 'OE CO 90ST-OV 
 
PLATE XLV. 
 
 147 
 
PLATE XLV. 
 
 c. Trapezoidal area, including central, middle s. Median septum, 
 
 lateral, and outside lateral muscle scars. v. Visceral cavity, 
 
 h. Central muscle scars. vs. Main vascular sinus, 
 
 j. Anterior lateral muscle scars. x. Heart-shaped cavity 
 ps. I'arietal band. 
 
 LlNGULELLA RADULA MattlieW (p. 529). . 
 
 Figure 1. Imperfect ca.st of the interior of a ventral valve from Locality 301x, Upper Cambrian sandstones of Divi- 
 sion 2c of Matthew's section, Dunns Shore, Simonds, near St. John, New Brunswick. University 
 of Toronto, Canada. 
 
 la. Cast of an interior of a ventral valve from Locality 301y, L'pper Cambrian sandstones of Division 2c, 
 east side of Courtney Bay, St. John, New Brunswick. University of Toronto, Canada. 
 
 lb. Slightly distorted ventral valve from the same locality as specimen represented by figure la. University 
 of Toronto, Canada. 
 
 Ic. Cast of the interior of a distorted ventral valve, associated with specimen represented by figure la. Uni- 
 versity of Toronto, Canada. 
 
 Id. Cast of the interior of a dorsal valve, the type specimen, showing central scars, etc., a.ssociated with the 
 specimen represented by figiu'e 1. University of Toronto, Canada. 
 
 Figures 1, la-d, and If are drawn from the specimens upon which Matthew based his figures [1891, PI. XV, figs. 
 7a-b and 8a-e], but closer identification is impossible. 
 
 le. Cast of the interior of a distorted ventral valve from the locality represented l)y figure la. Museum of 
 Comparative Zoology, Cambridge, Massachusetts. 
 
 If. Cast showing part of the interior of a dorsal valve, associated with the specimens represented by figures 
 la-c. University of Toronto, Canada. (See note following the description of figure Id.) 
 
 Ig. Small ventral valve, preser\-ing the exterior surface and convexity of outline in an unusually perfect 
 manner. Locality same as specimen represented by figure la. Museum of Comparative Zoology, 
 Cambridge, Massachusetts. (See note in description of figures Ik and 11.) 
 
 Ih. Interior of a ventral valve, preserving the form of the heart-shaped cavity as in Obolus, Locality same 
 as specimen represented by figure la. Museum of Comparative Zoology, Cambridge, ilassachusetts. 
 
 li. Cast of the interior of a ventral valve, sho\ving the \-isceral cavity and main vascular sinuses with unusual 
 clearness. Locality same as specimen represented by figure la. Museum of Comparative Zoology, 
 Cambridge, Massachusetts. 
 
 Ij. Cast of the interior of a dorsal valve, showing muscle scars, etc., beautifully preserved. Locality same as 
 specimen represented by figiu-e la. Museum of Comparative Zoology, Cambridge, Massachusetts. 
 
 Ik and 1 1. Interior of dorsal valve and cast of same. Locality same as specimen represented by figure la. 
 Museum of Comparative Zoology, Cambridge, Mas.sachusetts. It may be that the specimens repre- 
 sented by figures Ig, Ik, and 1 1 represent a small species distinct from Lingiilella raditla. All of the 
 specimens are more or less distorted in the arenaceous shales in which (hey are embedded. 
 
 LlNGULELLA TRIPARILIS (MattllCW) (p. 536). 
 
 [Text figs. 44a-;, p. 537.] 
 
 Figure 2. Broad form of ventral valve from Locality 13t', Middle Cambrian sandstones of Division Elb on Dugald 
 
 Brook, Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. No. 57013a. 
 2a and 2a'. Narrow form of ventral valve associated with the specimen represented by figure 2. U. S. Nat. 
 
 Mus. Cat. No. 57013b. 
 2b. Ventral valve on which a portion of the exterior surface of the shell is preserved. Associated with the 
 
 specimen represented by figure 2. U. S. Nat. Mus. Cat. No. 57013c. 
 2c. Cast of interior of a dorsal valve associated with the specimen represented by figure 2. I'. S. Xat. Mus. 
 
 Cat. No. 57013d. 
 2d. Cast of interior of a dorsal valve from Locality 13t", Middle Cambrian sandstones of DiWsions Elc and Eld, 
 
 on Dugald Brook, Cape Breton, Nova Scotia. V. S. Nat. Mus. Cat. No. 57012a. 
 2e. Narrow form of dorsal valve associated with the specimen represented by figure 2, preser\-ing a portion 
 
 of the outer shell, with side outline. U. S. Nat. Mus. Cat. No. 57013e. Another specimen (Cat. 
 
 No. 51855a, from Locality 13t) was used in restoring certain portions of this figure. 
 2f. Broad form of dorsal valve, associated with the specimen represented by figure 2. U. S. Nat. Mus. Cat- 
 No. 57013f. 
 148 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XLV 
 
 PS y.i. 
 
 2"' 
 
 i 
 
 PRANCES WIESER DEL. 
 
 HELioTYPE CO eosi 
 
PLATE XLV. 149 
 
 LiNGULELLA (LiNGTJLEPis) PUMiLA (Matthew) (p. 556). 
 
 Figure 3. Exterior of ventral valve, the type specimen. University of Toronto, Canada. 
 3a. Exfoliated dorsal valve, showing muscle scars. University of Toronto, Canada. 
 
 Figures 3 and 3a are drawn from the specimens illustrated by Matthew [1903, PI. VII, figs. 5a and 5b, respectively]. 
 The specimens represented are both from Locality 344f, Middle Cambrian, shalesof the Coldbrook of Matthew, on Dugald 
 Brook, Cape Breton, Nova Scotia. 
 
PLATE XL VI. 
 
 151 
 
PLATE XLVI. 
 
 a. Central lateral space of area. f. Flexure line of area, 
 
 a'. Outer lateral space of area. p. Tedicle groove. 
 
 c. Trapezoidal area, including central, middle v. Visceral cavity, 
 lateral, and outside lateral muscle scars. 
 
 Obolus (Westo?:ia) aurora (Hall) (p. 451). 
 
 Figure 1. Compressed ventral valve, from which the outer shell has been exfoliated. Locality S85x, Upper Cambrian 
 
 sandstone near Mazomanie, Dane County, Wisconsin. U. S. Nat. Mus. Cat. No. 51681a. The area 
 
 is enlarged in figure Ic. 
 la. Cast of the interior of a compressed ventral xalve associated with the specimen represented by figure 1. 
 
 The visceral area (v) recalls the heart-shaped pit of Lingulella anitangida (PI. XVII, fig. If). The 
 
 central muscle scars were located in the area (c), but are not clearly defined. IJ. S. Nat. Mus. Cat. 
 
 No. 51681b. 
 lb. Compressed ventral valve associated with the specimen represented by figure 1, showing concentric and 
 
 radiating lines and strise as preserved on the cast of the interior of the shell. U. S. Nat. Mus. Cat. 
 
 No. 51681c. The area is enlarged in figure Id. 
 Ic. Enlargement of the area of figure 1. U. S. Nat. Mus. Cat. No. 51681a. 
 Id. Enlargement of the area of figure lb, to show the apron-like area mentioned in the text (p. 452). U. S. 
 
 Nat. Mus. Cat. No. 51681c. 
 le. Cast of the exterior of a dorsal valve associated with the specimen represented by figure 1. U. S. Nat. 
 
 Mus. Cat. No. 51681d. 
 If. Cast of the interior of a dorsal vahe associated with the specimen represented by figure 1. The shell is 
 
 compressed and the area broken at x'. U. S. Nat. Mus. Cat. No. 516Sle. 
 Ig. Enlargement of a portion of the central part of the surface of the shell figured in ]h, to show the irregular 
 
 lamellose character of the striae. Locality 85s, Upper Cambrian sandstone at Prairie du Sac, Sauk 
 
 County, Wisconsin. U. S. Nat. Mus. Cat. No. 51G80a. 
 Ih. Part of the shell represented in figure Ig, greatly enlarged by photography to illustrate the character of 
 
 the outer surface. U. S. Nat. Mus. Cat. No. 61680a. 
 1.52 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XLVI 
 
 FRANCES W'ESER DEL. 
 
 MELlOTypE CO BCSl 
 
PLATE XLVII. 
 
 153 
 
PLATE XL VII. 
 
 a. Central lateral space of area. p. Pedicle groove, 
 
 a'. OutfT lat^?ral space of area. ps. Parietal band, 
 
 f. Fle-Kure line of area. s. Median septum, 
 
 h. Central muscle scar. v. Vi.sceral cavity. 
 
 i. Transmedian muscle scar. vs. Main vascular sinus, 
 
 j. Anterior lateral muscle scar. 
 
 Obolus (Westonia) ell.\ (Hall and Whitfield) (p. 455). 
 
 |PI. XXXIII. figs. 3, 3a-c.] 
 
 Figure 1. Ventral valve laterally compressed and flattened, from Locality 30a, Middle Cambrian siliceous shale in 
 
 Big Cottonwood Canyon, southeast of Salt Lake City, Utah. V . S. Nat. Mus. Cat. No. 51691a. 
 la. Dorsal valve associated in the same bed of shale vrith specimen represented by figure 1, but it is not com- 
 pressed laterally. Neither specimen preserves any of the shell substance. V. S. Nat. Mus. Cat. No. 
 
 51691b. 
 lb. Enlarged figure of the type specimen, a dorsal valve, from Locality 329, Middle Cambrian shales near 
 
 Calls Fort, Boxelder County, Utah. U. S. Nat. Mus. Cat. No. 15321a. Specimen figured by Hall 
 
 and \\Tiitfield [1877, PI. I, fig. 8] as Lingidepis ella; and by Walcott [1886b, PI. VIII, fig. 4; and 1891a, 
 
 PI. LXVII, fig. 2b] as Lingulella ella. 
 Ic. Cast of the interior of a slightly distorted ventral valve from Locality 329e, Middle Cambrian siliceous 
 
 shales of East Canyon, above Ophir, Oquirrh Range, Tooele County, L'tah. U. S. Nat. Mus. Cat. 
 
 No. 1.5320a. 
 Id. Another cast of the interior of a ventral valve that is associated with the specimen represented by figure 
 
 Ic, but which has suffered less from distortion. U. S. Nat. Mus. Cat. No. 1.5320b. Specimen figured 
 
 by Walcott [lS98b, PI. XXVIII, fig. 7] as Oholus {Lingulella) ella. 
 le and If. Ventral and dorsal valves of young shells associated with the shells represented by figures 1 and 
 
 la. U. S. Nat. Mus. Cat. Nos. 51691c and 51691d, respectively. 
 Ig. Impression of the interior of a ventral valve from Locality 302s, Middle Cambrian shale in Last Chance 
 
 Gulch, south of Helena, Montana. U. S. Nat. Mus. Cat. No. 516S6a. Specimen figured by Walcott 
 
 [1898b, PI. XXVIII, fig. 5] as Obolus (Lingulella) ella. 
 Ih and li. Interior casts of ventral and dorsal valves flattened in argillaceous shales of Locality 31, Middle 
 
 Cambrian, at the Chisholm mine, near Pioche, Nevada. LT. S. Nat. Mus. Cat. Nos. 15319a and 1.5319b, 
 
 respectively. The specimen represented by figure li was figured by Walcott [1898b, PL XXVIII, 
 
 fig. 8] as Obolus {Lingulella) ella. 
 Ij. Cast of the interior of a small ventral valve with a very high area, from Locality 4g, Middle Cambrian shale 
 
 1 mile north of the forks of East and West Gallatin rivers, Montana. L'. S. Nat. Mus. Cat. No. 51GS5a. 
 Ik. Impression of the interior of a slightly distorted dorsal valve from the same locality as specimen repre- 
 sented by figure Ig, showing the characteristic muscular impressions. U. S. Nat. Mus. Cat. No. 
 
 51686b. Specimen figured by Walcott [1898b, PI. XXVIII, fig. 6] as Obolus (Lingulella) ella. 
 1 1. Interior of finely preserved dorsal valve from Locality 5h, Middle Cambrian shales 2 miles southeast of 
 
 Malade, Idaho. U. S. Nat. Mus. Cat. No. 51689a. 
 Im. Enlargement of a small individual associated with the shells repre.sented by figures Ih and li, showing 
 
 characteristic surface markings. V . S. Nat. Mus. Cat. No. 15319c. The counteq^art of this specimen 
 
 (Cat. No. 15319d) was used to aid in restoring certain portions of figure Im. 
 In. Cast of an interior of a ventral valve associated with the ventral valve represented by figure Ij. L^ S. 
 
 Nat. Mus. Cat. No. 5168.5b. 
 lo. Enlargement by photography of the surface of a specimen associated with the shell represented by figure 
 
 Ij. U. S. Nat. Mus. Cat. No. 51685c. 
 Ip. Distorted ventral valve from Locality 90, Middle Cambrian shales near Craigs Mountain, Cherokee County, 
 
 Alabama. U. S. Nat. Mus. Cat. No. 51634a. 
 154 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XLVII 
 
 PRANCES WIESER DEL. 
 
 : CO BOSTON 
 
PLATE XL VIII. 
 
 155 
 
PLATE XLVIII. 
 
 h. Central muscle scar. vs. Main vascular sinus. 
 
 1. Outside lateral muscle scar. x. Heart-shaped cavity. 
 
 V. Visceral cavity. 
 
 Obolus (Westonia) euglyphus (Walcott) (p. 461). 
 
 Figures 1 and la. Two aasiociatod, partly exfoliated ventral valves that illustrate variation in form, and the strong 
 lamellje of the anterior portion of the shell. Locality 74, Middle Cambrian sandstone at the head of 
 Nunkoweap Valley, Grand Canyon of the Colorado, Arizona. U. S. Nat. Mus. Cat. No. 2731Ca and 
 27316b, respectively. 
 
 lb. Exfoliated ventral valve associated with the specimens represented by figures 1 and la, showing the fine 
 radiating strise on the inner layer of the shell. U. S. Nat. Mus. Cat. No. 27316c. 
 
 Ic. Cast of the interior of a ventral valve, the type specimen, associated with the Bpecimens represented by 
 figures 1 and la, showing the character of the area, visceral cavity, and main vascular sinuses. U. S. 
 Nat. Mus. Cat. No. 273l6d. 
 
 Id. Cast of the interior of a ventral valve from Locality 74c, Middle Cambrian sandstone at the head of Lava 
 Canyon, Grand Canyon of the Colorado, Arizona. U. S. Nat. Mus. Cat. No. 57023a. 
 
 le. Cast of the interior of a dorsal valve, associated with the specimen represented by figure Id. L^. S. Nat. 
 Mus. Cat. No. 57023b. Another specimen (Cat. No. 27316e from Locality 74) was used to aid in restor- 
 ing certain portions of this figure. 
 
 If. Enlargement of a portion of the surface near the umbo, to illustrate the irregular inosculating strise. 
 Associated with the shells represented by figures 1 and la. U. S. Nat. Mus. Cat. No. 27316f. 
 
 LiNGtILELLA LIXEOLATA (Walcott) (p. 515). 
 
 FiGUBE 2. Small, obtuse ventral valve from which the shell has been largely exfoliated. Locality 73a, Middle Cam- 
 brian sandstone in Chuar Valley, CJrand Canyon of the Colorado, Arizona. U. S. Nat. Mus. Cat. No. 
 27324a. 
 
 2a. Acuminate ventral valve associated with the shell represented by figure 2, showing a portion of the inner 
 layers, marked by fine radiating stri.f. U. S. Nat. Mu.-!. Cat. No. 27324b. 
 
 2b. Very perfect dorsal valve, the type specimen, from Locality 73, Middle Cambrian sandstones in Kwagunt 
 Valley, Grand Canyon of the Colorado, Arizona. V. S. Nat. Mus. Cat. No. 27325a. 
 
 2c and 2d. Partly exfoliated dorsal valves associated with the shell represented by figure 2. U. S. Nat. 
 Mus. Cat. Nos. 27324c and 27324d, respectively. 
 
 2e and 2f . Associated ventral and dorsal valves from Locality 74, Middle Cambrian sandstones at the head of 
 Nunkoweap Valley, Grand Canyon of the Colorado, Arizona. U. S. Nat. Mus. Cat. Nos. 27326a and 
 27326b, respectively. 
 
 2g. Partly exfoliated dorsal valve, more broadly oval than usual, associated with the shell represented by 
 figure 2b. U. S. Nat. Mus. Cat. NcJ. 27325b. 
 
 2h. A very fine illustration of a rather large dorsal valve, associated with the shell represented by figure 2b. 
 U. S. Nat. Mus. Cat. No. 27325c. 
 
 2i and 2j. United ventral and dorsal valves with side view, from Locality 74d, Middle Cambrian sandstone in 
 Bass Canyon, Grand Canyon of the Colorado, Arizona. U. S. Nat. Mus. Cat. No. 51820a. 
 
 2k and 21. Casts of rather large ventral and dorsal valves that are referred to this species. They are associ- 
 ated with the shell represented by figure 2. U. S. Nat. Mus. Cat. Nos. 27324e and 27324f, respectively. 
 
 Obolus (Westonia) finlandensis Walcott (p. 462). 
 
 Figure 3. Exterior of ventral valve, the type specimen, illustrating form and surface characters. IT. S. Nat. Mus. 
 Cat. No. 35296a. 
 3a. Partly exfoliated dorsal valve. U. S. Nat. Mus. Cat. No. 35296b. 
 3b. Cast of part of interior of dorsal valve. U. S. Nat. Mus. Cat. No. 3529r)C. 
 
 The specimens represented are all from Locality 311x, Middle Cambrian limestone at Saltvik, Aland Island, 
 Finland. 
 
 156 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XLVIIl 
 
 FRANCES WIE8ER DEL. 
 
 HCLIOTVPE CC BOSTON 
 
PLATE XLVIII. 157 
 
 Obolus (Westonia) bottnicus (Wiman) (p. 454). 
 
 Figures 4 and 4'. Top and side viewM of an almoat perfectly preserved ventral valve, the type specimen. Specimen in 
 
 the collection of the University of Upsala, Sweden; cast in the United States National Musenm 
 
 (Cat. No. 57089a). 
 4a. Exterior of a partly exfoliated dorsal valve. Specimen in the collection of the University of Upsala, 
 
 Sweden; cast in the United States National Museum (Cat. No. 57089b.) 
 4b. Imperfect cast of the interior of a dorsal valve. Specimen in the collection of the University of Upsala, 
 
 Sweden; cast in the United States National Museum (Cat. No. 57089c). 
 4c. Interior of a dorsal valve. Specimen in the collection of the University of Upsala, Sweden; ca.st in the 
 
 United States National Museum (Cat. No. o7089d). 
 
 Figures 4, 4a-c are drawn from the specimens illustrated by Wiman [1902, PI. II, figs. 41^4, respectively] as 
 Lingula hottnica. The specimens represented are all from Locality 311, Middle? Cambrian drift bowlder of sandstone 
 on Eggegrund Island, Gefle Bay, Sweden. 
 
 Obolus (Westonia) wimani Walcott (p. 467). 
 
 Figure 5. Exterior of ventral valve from Locality 311c, Middle? Cambrian drift bowlder No. 7 on Biludden, 
 Gefle Bay, Sweden. Specimen in the collection of the L^niversity of Up.sala, Sweden; cast in the 
 United States National Museum (Cat. No. 57090a). Type specimen, figured by Wiman [1902, PI. II, 
 fig. 30] as Lingalella sp. No. 1. 
 
 5a. Exterior of ventral valve from Locality 311g, Middle? Cambrian drift bowlder No. 16 on Biludden, 
 Gefle Bay, Sweden. Specimen in the collection of the University of Upsala, Sweden; cast in the 
 United States National Museum (Cat. No. 57091a). Specimen figured by Wiman [1902, PI. II, fig. 
 31] as LinguleUa sp. No. 2. 
 
 5b. Partly exfoliated dorsal valve from Locality 3Ht, Middle ? Cambrian drift bowlder at Ofverby, Aland 
 Island, Finland. Specimen in the collection of the ITniversity of L'psala, Sweden; cast in the United 
 States National Museum (Cat. No. 57092a). Specimen figured by ^\■iman [1902, PI. II, fig. 32] as 
 LinguleUa sp. No. 7. 
 
 Obolus (Westonia) alandensis Walcott (p. 4,51). 
 
 Figure 6. Exterior of ventral valve from Locality 311j, Middle? Cambrian drift bowlder No. 28 on Biludden, 
 Gefle Bay, Sweden. Specimen in the collection of the University of Upsala, Sweden; cast in the 
 United States National Museum (Cat. No. 57093a). Specimen figured by Wiman [1902, PI. II, fig. 
 33] as LinguleUa? sp. No. 3. 
 6a. Exterior of a dorsal valve from Locality 311y, Middle? Cambrian drift bowlder at Ytternas, Aland Island, 
 Finland. Specimen in the collection of the ITniversity of L'psala, Sweden; cast in the United States 
 National Museum (Cat. No. 57094a). Type specimen, figured by Wiman [1902, PI. II, fig. 35] as 
 LinguleUa? sp. No. 5. 
 
 Obolus (Westonia) balticus Walcott (p. 453). 
 
 Figure 7. Partly exfoliated ventral valve from Locality 311t, Middle? Cambrian drift bowlder at Ofverby, Aland 
 Island, Finland. Specimen in the collection of the University of Upsala, Sweden; cast in the L'nited 
 States National Museum (Cat. No. 57095a). Specimen figured by Wiman [1902, PI. II, fig. 34] as 
 LinguleUa? sp. No. 6. 
 
 7a. Dorsal valve from Locality 311o, Middle? Cambrian drift bowlder on Skalstenarne Island, Gefle Bay, 
 Sweden. Specimen in the collection of the University of Upsala, Sweden; cast in the United States 
 National Museum (Cat. No. 57090a). Specimen figured by Wiman [1902, PI. II, fig. 37] as LinguleUa? 
 sp. No. 4. 
 
 7b. Dorsal valve from Locality 311h, Middle? Cambrian drift bowlder No. 26, on Biludden, Gefle Bay, 
 Sweden. Specimen in the collection of the University of Upsala, Sweden; cast in the United States 
 National Museum (Cat. No. 57097a). Type specimen, figured by Wiman [1902, PI. II, fig. 3S] as 
 LinguleUa? sp. No. 4. 
 
PLATE XLIX. 
 
 159 
 
PLATE XLIX. 
 
 a. Central lateral space of area. 
 
 c. Trapezoidal area, including central, middle 
 
 lateral, and outside lateral muscle scars, 
 h. Central muscle scar, 
 i. Transmedian muscle scar. 
 j. Anterior lateral muscle scar. 
 
 k. Middle lateral muscle scar. 
 1. Outside lateral muscle scar. 
 p. Pedicle groove. 
 V. Visceral cavity, 
 vs. Main vascular sinus. 
 X. Heart-shaped cavity. 
 
 Obolus (Westonia) escasoni (Matthew) (p. 459). 
 
 Figure 1. Cast of the interior of a ventral valve, showing continuation of cast of pedicle furrow, with the central 
 
 depres.sion of the \'isceral area. University of Toronto, Canada, 
 la. Interior of ventral valve, showing heart-shaped ca\'ity and position of central muscle scars; also a strongly 
 
 pitted and striated interior surface. University of Toronto, Canada. Type specimen, figured by 
 
 Matthew [1901a, PI. V, fig. Ig] as Lingulella if) escasoni. 
 laa. Enlargement of the central portion of figure la to show the position and size of the muscle scars, surface 
 
 pits. etc. 
 lb. Cast of the inteiior of a rather large dorsal valve. University of Toronto, Canada. Specimen is probably 
 
 the one illustrated Ijy Matthew [1901a, PI. V, fig. Id] as Lingulella (f) escasoni. 
 Ic. Id, and le. Interior of dorsal valves, showing the position, of muscle scars. University of Toronto, Canada. 
 If. Enlargement of the exterior surface of a shell 3 mm. long, to show radiating strise, lines of growth, and 
 
 transverse undulating lines. University of Toronto, Canada. 
 
 The figiues are all drawn from specimens in Matthew's figured material, but except in the cases noted (figs, la 
 and lb) identification is impossible. The specimens represented are all from Locality 325, Upper Cambrian shales on 
 McAdam Shore, East Bay, Cape Breton, Nova Scotia. 
 
 Obolus (Westoxia) stoneanus (Whitfield) (p. 465). 
 
 (PI. XXVIII, flgs. 2,2a-g.l 
 
 Figure 2. A dorsal valve from Locality lie, Upper Camlwian sandstone near Newton. New Jersey. 
 2a. Enlargement of the exterior surface of the specimen represented by figure 2. 
 
 The specimen represented was figiu'ed by Weller [1903, PI. I, fig. 6] as Lingulella stoneana. 
 
 Lingulella texana Walcott (p. 535). 
 
 Figure 3. Partly exfoliaoed doi-sal valve, showing strong radiating striae which characterize the species. Locality 
 69, LTpper Cambrian limestone near Honey Creek, Burnet County, Texas. U. S. Nat. Mus. Cat. 
 No. .51805a. 
 3a. Cast of a dorsal valve, the iype specimen, showing the area and muscle scars. Locality 70, Upper Cam- 
 brian limestone near Morgans Creek, Burnet County, Texas. U. S. Nat. Mus. Cat. No. 51806a. Copied 
 from Walcott [1908d. PI. VIII, fig. 5]. 
 
 Obolus (Westonia) iphis Walcott (p. 462). 
 
 Figures 4 and 4'. Ventral \al\e from which the outer layer of shell has been exfoliated. Locality 64, Upper Cam- 
 brian limestone near llie Bullwhacker mine. Eureka district, Nevada. V. S. Nat. Mus. Cat. No. 
 51720a. 
 
 4a and 4a'. Partly exfoliated dorsal valve from Locality 201a, Lower Ordov-ician limestone east of Ham- 
 burg Ridge, Eureka district, Nevada. L'. S. Nat. Mus. Cat. No. 51542a. 
 
 4b. Dorsal vahe preserving most of the outer layer of the shell, the type specimen, associated with the 
 shell represented by figure 4a. U. S. Nat. Mus. Cat. No. 51542b. 
 
 4c. Dorsal valve associated with the shell represented by figure 4. U. S. Nat. Mus. Cat. No. 51720b. 
 
 4d. Enlargement of a portion of the outer surface of the shell represented in figure 4b. U. S. Nat. MiLt. 
 Cat. No. 51-542b. 
 160 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XLIX 
 
 FRANCE6 WIESER 0£L. 
 
PLATE XLIX 161 
 
 Obolus (Westonia) wasatchensis Walcott (p. 466). 
 
 [Text figs. 41A~F, p. 407.] 
 
 Figure 5. Compressed and crushed ventral valve. U. S. Nat. Mum. Cat. No. 57098a. 
 
 5a. Dorsal valve flattened in the siliceous shale. U. S. Nat. Mus. Cat. No. 57098b. 
 
 The specimens represented are both from Locality 32x, Middle Oambrian shale in Wasatch Canyon, Boxelder 
 County, Utah. 
 
 Obolus (Westonua.) ella onaquiensis Walcott (p. 459). 
 
 Figure 6. Compressed, exfoliated dorsal valve, the type specimen. U. S. Nat. Mus. Cat. No. 51716a. 
 
 6a. Enlargement of the surface of another specimen to show the zigzag, transverse strise. U. S. Nat. Mus. 
 Cat. No. 51716b. 
 
 The specimens represented are both from Locality 33f, Middle Cambrian shales, Onaqui Range. Tooele County, 
 Utah. 
 
 62667°— VOL 51, pt 2—12 11 
 
PLATE L. 
 
 163 
 
PLATE L. 
 
 a. Central lateral space of area, 
 a'. Outer lateral space of area. 
 
 b. Bo.vS (see text description, p. .571). 
 
 c. Trapezoidal area, including central, middle 
 
 lateral, and outside lateral muscle scars, 
 f. Flexure line of area. 
 Umbonal muscle scar. 
 Central muscle scar. 
 
 h. 
 
 i. Transmedian muscle scar. 
 
 j. Anterior lateral muscle scar. 
 
 k. Middle lateral muscle scar. 
 
 1. Outside lateral muscle scar, 
 mr. Median ridge. 
 
 p. Pedicle groove, 
 ps. Parietal band. 
 
 s. Median septum, 
 vs. Main vascular sinus. 
 
 X. Heart-shaped cavity. 
 
 BiciA GEMMA (Billings) (p. 569). 
 
 Figures 1 aud lb. Exterior and side view of a ventral valve with the outer siu'faee parlly removed by erosion. 
 
 Locality 27, Lower Cambrian limestone near Troy, Rensselaer County, New York. U. S. Nat. Mus. 
 
 Cat. No. 15349a. 
 la. Exterior of a ventral valve associated with the specimen represented by figure 1, preserving the interrupted 
 
 radiating stride of the outer surface. U. S. Nat. Mus. Cat. No. 15349b. 
 Ic and Ic'. Exterior of two dorsal valves, associated with the specimen represented by figure 1. L'. S. 
 
 Nat. Mus. Cat. Nos. lo349c and 15349d, respectively. Specimen figured by Walcott [1886b, PI. X, 
 
 fig. 2e] as Obolella gemma. 
 Id. Posterior portion of a ventral valve associated with the shell represented by figure 1. on which the con- 
 centric and radiating lines are very strong (.«ee fig. le). U. S. Nat. Mus. Cat. No. 15349e. 
 le. Outer surface of a ventral vah'e from Locality 2b, Lower Cambrian limestone near Beman Park, Troy, 
 
 New York, greatly enlarged. This may possibly be the surface of Bicia U'hitearesi. V. S. Nat. Mus. 
 
 Cat. No. 51900a. 
 If. Natiu'al cast of interior of ventral vahe from Locality 2o, Lower Cambrian limestone bowlders at east 
 
 entrance to Bic Harbor, Quebec. U. S. Nat. Mus. Cat. No. 14889d. 
 Ig. Nattrral cast of interior of ventral valve associated with the specimen represented by figure le, at Troy, 
 
 New York. L'. S. Nat. Mus. Cat. No. 51900b. .\nother specimen (Cat. No. 51900c) was used to aid 
 
 in restoring certain portions of this figure. 
 Ih, li, and Ik. Interiors of ventral valves showing variation in area, thickening of shell, etc. They are 
 
 associated with the specimen represented by figure If, at Bic Harbor, Canada. L'. S. Nat. Mus. Cat. 
 
 Nos. 14S89C, 148S91), and 14889a, respectively. The specimens represented by figures li and Ik were 
 
 illustrated by Walcott [188Gb, PI. X, figs. 2b and 2d. respectively] as Ohohlla getnma. The specimen 
 
 illustrated by Walcott [1886b, PL X, fig. 2] is not figured in this monograph. 
 Ij. Interior of ventral valve, with thick shell growth, from Locality 27, Lower Cambrian limestone near 
 
 Tro)', New York. U. S. Nat. Mus. Cat. No. 1.5349e. Specimen figured by Walcott [1886b, PI. X, 
 
 fig. 2c] as Obolella gemma. 
 11. Natural cast of a distorted dorsal valve associated with the specimen represented by figure le, at Troy, 
 
 New York. U. S. Nat. Mus. Cat. No. 51900d. 
 Im. Interior of a dorsal valve associated with the .'ihcll represented by figure If at Bic Harbor, Canada. V.S. 
 
 Nat. Mus. Cat. No. 14889f. 
 In. Interior of dorsal valve from Locality 2b, Lower Cambrian limestone near Beman Park, Troy, New York. 
 
 U. S. Nat. Mus. Cat. No. 51900e. This drawing is based on one fairly well preserved interior, but 
 
 the anterior lateral muscle scars and some other details arc taken from five other associated specimens 
 
 (Cat. Nos. D1900f-i). 
 
 BiciA WHiTEAVESi Walcott (p. 570). 
 
 Figures 2, 2a, and 2b. Interiors of ventral valves, showing transition from short form of ventral valve of B. gemma, 
 figure Ik, to the typical ventral vaWe of B. uhilearrni, figure 2c. U. S. Nat. Mus. Cat. Nos. 35260a, 
 3.5260b. and 3.5260c, respectively. 
 
 2c. Interior of a ventral valve, the type specimen. L'. S. Nat. Mus. Cat. No. 35260d. 
 
 2d, Natural cast of the interior of the specimen represented by figure 2c. U. S. Nat. Mus. Cat. No. 35260e. 
 
 2e. Interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 35260f. 
 
 The specimens represented are all from Locality 2b. Lower Cambrian limestone near Beman Park, Troy. New 
 
 York. 
 
 164 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. L 
 
 / 
 
 y 
 
 .♦> r'\ 
 
 ■ V vs 
 
 K >> 
 
 4 
 
 r^' 
 
 2" 
 
 FRANCES W1E8ER OEL. 
 
 V VS 
 
 HELIOTYPE CO., BOSTON. 
 
PLATE LI. 
 
 165 
 
PLATE LI. 
 
 I. Flexure lines. 
 h. Central muscle scar, 
 i. Transmedian muscle scar, 
 j. Anterior lateral muscle scar. 
 1. Outside lateral muscle scar, 
 p. Pedicle groove, 
 r. Area of posterior adductor scar. 
 
 r'. Areaof anterior adductor scar 
 s. Median septum. 
 V. Visceral cavity, 
 vs. Vascular sinus. 
 
 ivs. Central lateral branches of vascular 
 system. 
 X. Ifeart-shaped cavity. 
 
 Elkania desiderata (Billings) (p. 562) 
 
 Figure 1. Interior of a ventral valve, showing reversed area and muscle scars. U. S. Nat. Mas. Cat. No. 51943a. 
 la. Cast of interior of a ventral valve. U. S. Nat. Mus. Cat. No. 51943b. 
 lb. Cast of interior of dorsal valve, showing main vascular sinuses with branches extended over central area. 
 
 U. S. Nat. Mus. Cat. No. 51943c. 
 Ic. Cast of interior of dorsal valve, showing central area defined, b"ut no traces of branches of main vascular 
 
 sinuses. This central area has been interpreted as probably the area of attachment of muscles, by 
 
 authors who have written of the species. IT. S. Nat. Mus. Cat. No. 51943d. 
 Id. Cast of interior of a dorsal valve in which the \dsceral area is beautifully defined, but the vascular sinuses 
 
 and the central area included within them are not defined. U. S. Nat. Mus. Cat. No. 51943e. 
 
 The specimens represented are all from Locality 319a, Lower Ordovician shales, at Point Levis, Quebec. 
 
 Elkania ambigua (Walcott) (p. 562). 
 
 Figure 2. Exterior of ventral valve. This specimen can not he located and the locality number Ls not known. The 
 figure, however, is a new drawing of the specimen illustrated by \Valcott [1884b, PI. I, fig. 2b] as 
 Obolellaf ambigua. 
 
 2a. Partly exfoliated dorsal valve, showing the outlines of the visceral area and main vascular sinuses on 
 the inner laraellations of the shell. U. S. Nat. Mus. Cat. No. 24554a. Type specimen, figured by 
 Walcott [1884b, PI. I, fig. 2a] as Obolellaf amUgua. 
 
 2b. Interior of a dorsal valve, showing visceral area, muscle scars, and main vascular sinuses. U. S. Nat. Mus. 
 Cat. No. 24554b. Specimen figured by Walcott [1884b, PI. I, fig. 2c] as Obolella f ambigua. 
 
 2c. Cast of the interior of a dorsal valve in which the thickening of the shell within the lines of the main vascu- 
 lar sinuses is greater than in any other specimen. The visceral area also extends farther forward 
 into the valve. This variation in the forward extension of the visceral area is not infrequent in 
 species of Obolus. U. S. Nat. Mus. Cat. No. 24554c, 
 
 The specimens represented by figures 2a-c are all from Locality 63, Lower Ordo\-ician limestone, northeast of 
 Adams Hill, Eureka district, Nevada. 
 
 Obolus (Fordinia) bellulus (Walcott) (p. 428). 
 
 Figure 3. Top and side views of a partly exfoliated ventral valve from Locality 7z, Upper Cambrian limestone, 
 about 3 miles southeast of Emigrant Pa.ss, Esmeralda County, Nevada. U. S, Nat. Mus. Cat. No. 
 51944g. 
 
 3a. Interior of a ventral valve, the type specimen, showing central trapezoidal area at x; also main vascular 
 sinuses, pedicle groove, etc. IT. S, Nat. Mus, Cat, No, 51944a. 
 
 3b and 3c. Caat.s of interior of ventral valves. V. S. Nat. Mus. Cat, Nos, 51944b and 51944c, respectively. 
 
 3d. Partly exfoliated dorsal valve. U. S. Nat. Mus. Cat. No. 51944d. 
 
 3e. Interior of dorsal valve. U. S. Nat. Mus. Cat. No, 51944c. 
 
 3f. Cast of interior of dorsal valve. U. S. Nat. Mus. Cat. No. 51944f. 
 
 The specimens represented by figures 3a-f are from Locality 7x, Upper Cambrian limestones about 2.5 miles 
 southeast of Emigrant Pass, Silver Peak quadrangle, Esmeralda County, Nevada. 
 166 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL, LI 
 
 ' r 
 
 J^^^k 
 
 nN 
 
 /I 
 
 Jf^S/ki^ 
 
 K \ 
 
 / 
 
 
 ^ 1 
 
 i' v/ 
 
 f 
 
 vl 
 
 FRANCES WIE8ER DEL. 
 
 MELtOTYPE CO ecSTON 
 
PLATE LI. 167 
 
 Elkania IDA (Billings) (p. 563). 
 
 [PI. XXX, figs. 20 and 20a.] 
 
 Figures 4 and 4a. Top and side views of a partly exfoliated ventral valve. Geol. Survey Canada. 
 
 4b. Cast of the interior of a dorsal valve, showing elevated visceral cavity and muscle scars. Geol. Survey 
 
 Canada. 
 4c. Interior of a ventral valve, preserving a portion of the reversed area. Geol. Survey Canada. 
 
 The specimens represented are all from Locality 3191. limestone No. 2 of Billings's section, at Point LevLs, Qncbec. 
 Obolus (Fordinia) gilberti Walcott (j). 429). 
 
 Figures 5, 5a, and 5c. Side and top views of ventral valves varying in outline and convexity. U. S. Nat. Mus. Cat. 
 
 Nos. 5194f)a, 51946c, and 51946d, respectively. Figure 5, the type specimen, is copied from Walcott 
 
 [1908d, PI. VII, tig. 16]. 
 5b. Interior of dorsal valve. U. S. Nat. Mus. Cat. No. 5194(ib. Copied from Walcott [1908d, PI. VII, fig. 15a]. 
 5d. Exterior of dorsal valve. U. S. Nat. Mus. Cat. No. 5194Ge. 
 
 The specimens represented are all from Locality lln. Middle Cambrian limestone southeast of Marjum Pass. 
 House Range, Utah. 
 
 Schuchertina CAMBRIA Walcott (p. 5S5). 
 
 Figures (i, 6', and 6". Exterior, side, and back views of a partly exfoliated ventral valve. U. S. Nat. Mus. Cat. 
 
 No. 51411a. 
 6a. Exterior of a large, partly exfoliated ventral valve with a slight median fold. U. S. Nat. Mus. Cat. No. 
 
 51411b. 
 6b. Cast of the interior of a ventral valve, the type specimen, showing flabelliform muscle scars. V. S. Nat. 
 
 Mus. Cat, No. 51411c. 
 6c. Interior of the ventral valve represented l3y figure 61), drawn from a cast of that specimen. U. S. Nat. 
 
 Mus. Cat. No. 51411c. Parts of this figure are restored from other specimens. 
 6d and 6d'. Top, back, and side views of a cast of the interior of a slightly distorted ventral valve. IT. S. 
 
 Nat. Mus. Cat. No. 51411d. 
 6e. Interior of the ventral valve represented by figure 6d, obtained by making a cast of that specimen. U. S. 
 
 Nat. Mus. Cat. No. 51411d. 
 6f. Top and side view of a cast of a dorsal valve. U. S. Nat. Mus. Cat. No. 51411e. 
 6g. Exterior of a dorsal valve. U. S. Nat. Mus. Cat. No. 51411f. 
 6h. Cast of the interior of a ventral valve. U. S. Nat. Mus. Cat. No. 51411g. 
 6i. Interior of tlie ventral valve represented by figure 6h obtained by making a cast of that specimen. U. S. 
 
 Nat. Mus. Cat. No. 5141 Ig. 
 6]'. Cast of the interior of a dorsal valve, showing mesial area and va.scular markings. U. S. Nat. Mus. Cat. 
 
 No. 51411h. 
 6k. Enlargement of the central portion of figure 6j. 
 
 6 1. Cast of the posterior portion of the interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 514111. 
 6m. Interior of the posterior portion of the dorsal valve represented by figure 6 1, obtained by making a cast 
 
 of that specimen. U. S. Nat. Mus. Cat. No. 514111. 
 
 The specimens represented by figures 6, 6a-m are from Locality 5k. Middle Cambrian limestones on the road to 
 Wolsey, about 8 miles south of Neihart. Little Belt Mountains, Montana. 
 
PLATE LII. 
 
 169 
 
PLATE IJI. 
 
 a. Area of dorsal valve. sh. Cast of exterior of cardinal area on eafh side 
 cl. Cardinal muscle scar. ot pedicle furrow, 
 
 h. Central scars. v. Visceral area, 
 
 p. Cast of pedicle groove. vs. Main vascular sinus, 
 s. Median septum. 
 
 DiCELLOMUS POLITUS (Hall) (]). 575). 
 
 [Text figs. ICA-B, p. 314, and 49A-B, p. 57C.] 
 
 Figure 1. Ventral valvo. Thospe.cLmenfrom which this figure was drawn can not now be located. The locality and 
 
 catalogue number are therefore unknown. 
 la. Ventral valve from Locality 98, Upper Cambrian sandstone at Eau Claire, Wisconsin. U. S. Nat. Mua. 
 
 Cat. No. 35211a. 
 lb. Exterior and side views of ventral valve from Locality 78a, Upper Cambrian sandstone on Mount Wash- 
 ington, near Eau Claire, Wisconsin. U. S. Nat. Mus. Cat. No. 27447a. 
 Ic and Id. Casts of interiors of ventral valves associated with the shell represented by figure la. V. S. Nat. 
 
 Mus. Cat. Nos. 3.5211b and 3.5211c, respectively. The specimen represented byfigtire Ic was figured 
 
 by Walcott [1899, PI. LX, fig. 4a]. 
 le. Partly exfoliated ventral valve in which the visceral area extends forward of the center of the valve. 
 
 Locality 82b, Upper Cambrian sandstone near Taylors Falls, Miimesota. U. S. Nat. Mus. Cat. 
 
 No. 51916a. 
 If. Dorsal valve associated with the shell represented by figure le. U. S. Nat. Mus. Cat. No. 5191Gb. 
 Ig and Ih. Exteriors and side outlines of dorsal A-alves associated with the shell represented by figure la. 
 
 U. S. Nat. Mus. Cat. Nos. 35211d and 3.5211e, respectively. 
 li. Interior of a ventral \alve, associated with the shell represented by figure la, showing excavated area on 
 
 each side of the median line of the flattened posterior margin. U. S. Nat. Mus. Cat. No. 35211f. 
 Ij. Interior of a ventral valve, associated with the shell represented by figure la, showing large composite 
 
 muscle scars (cl), median septum (s), vascular sinuses (vs), and area. U. S. Nat. Mus. Cat. No. 3.5211g. 
 
 Specimen figured by Walcott [1899, PL LX, fig. 4]. 
 Ik. Cast of interior of a dorsal valve associated with the shell represented by figure la. 1^. S. Nat. Mus. Cat. 
 
 No. 3.521 Ih. 
 2 and 2a. Partly exfoliated ventral valves from Locality 3S5e, Upper Cambrian sandstone. Black Hills, 
 
 South Dakota. U. S. Nat. Mus. Cat. Nos. 51924a and 51924b, respectively. 
 2b. Partly exfoliated ventral valve from Locality 167. Middle Cambrian sandstone 9 miles west of Custer, 
 
 Black Hills, South Dakota. U. S. Nat. Mus. Cat. No. 51919a. 
 2c. Partly exfoliated dor.sal valve associated with the shells represented by figures 2 and 2a. L'. S. Nat. 
 
 Mus. Cat. No. 51924c. 
 2d, 2e, and 2f. Partly exfoliated dorsal valves associated with the shell represented by figure 2b. U. S. 
 
 Nat. Mus. Cat. Nos. 51919b, 51919c, and 51919d. respectively. 
 2g. Exterior of a ventral valve from Locality 356, Middle Cambrian sandstones on Red Canyon Creek, Black 
 
 Hills, South Dakota. U. S. Nat. Mus. Cat. No. 24593a. Specimen figured by Whitfield [1880, PI. II, 
 
 fig. 13] as Oholella polita. The specimen represented by figure 12 of Whitfield's paper is not figured 
 
 in this monograph. 
 2h. Ventral valve from Locality 35Se, L'pper Cambrian sandstone. Black Hills, South Dakota. U. S. Nat. 
 
 Mus. Cat. No. 1027a. Specimen figured by Meek and Hayden [1865, PI. I, figs. 2a-b] as Linffidepis 
 
 prima. 
 21. Dorsal valve associated with the ventral valve represented by figure 2h. U. S. Nat. Mus. Cat. No. 1027b. 
 
 3. Partly exfoliated dorsal valve, from Locality 302k. Middle Cambrian limestones, near Gallatin, Montana. 
 
 U. S. Nat. Mus. Cat. No. 51923a. 
 
 4. Ventral valve, broadened by distortion and partly exfoliated. U. S. Nat. Mus. Cat. No. 51913a. 
 4a. Dorsal valve, broadened by distortion. U. S. Nat. Mus. Cat. No. 51913b. 
 
 The specimens represented by figures 4 and 4a are both from Locality 302s, Middle Cambrian shale 1.5 miles 
 eoutb of Helena, Montana. They are somewhat doubtfully referred to this species. 
 
 Figure 5. Partly exfoliated ventral valve. U. S. Nat. Mus. Cat. No. 51921a. 
 
 5a. Exterior view and side outline of dorsal valve. U. S. Nat. Mus. Cat. No. 51921b. 
 5b. Fragment of cast of interior of a <lorsal valve. U. S. Nat. Mus. Cat. No. 51921c. 
 
 The specimens represented by figures 5, 5a-b are all from Locality 329b, Middle Cambrian limestone, collected 
 by the Wheeler Survey in Utah. 
 170 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. Lll 
 
 fRANCES WIESEH DEL. 
 
 KGl-IOTVPE CO B3STOI* 
 
PLATE LII. 171 
 
 DiCELLOMUS PECTENOIDES (Wllitfield) (]). 575 . 
 [Textflgs. 48A-B,p. 575.] 
 
 Figure 6. A transverse, partly exfoliated ventral valve from Locality 35Sb, Middle Cambnan sandstone on Castle 
 
 Creek, Black Hills, South Dakota. U. S. Nat. Mua. Cat. No. 24592a. Specimen figured by Whif^ 
 
 field [ISSO, PI. II, fig. 18] as Obolus? pecterioides. This may be the type specimen, but it can not 
 
 be identified with any of Whitfield's figures [1875, unnumbered plate, figs. 1-3]. 
 
 6a. Partly exfoliated dorsal valve associated with the shell represented by figure 6. U. S. Nat. Mus. Cat 
 
 No. 24.592b. Specimen figured by Whitfield [1880, PI. II, fig. 19] as Obolus f pectenoides. 
 6b. Cast of interior of a ventral valve from Locality 164, Middle Cambrian sandstone near Deadwood, Black 
 Hills, South Dakota. U. S. Nat. Mus. Cat. No. 51911a. 
 
 6c. Cast of interior of a dorsal valve associated with the shell represented by figure 6b U S Nat Mus 'Cat 
 No. 51911b. ■ ' 
 
 DiCELLOMUS sp. undt. Walcott (p. 578). 
 
 FiGDREs 7 and 7a. Exterior and side views of a dorsal valve, from Locality 3101, Middle Cambrian at Andrarum, 
 Pro\dnee of Christianstad, Sweden. U. S. Nat. Mus. Cat. No. 58304. 
 
PLATE LIII. 
 
 173 
 
PLATE LIII. 
 
 c. Trapezoidal arta, including central, 
 middle lateral, and outside lateral 
 muscle scars. 
 
 el. Cardinal scars. 
 
 h. Central muscle scar. 
 
 i. Transmcdian muscle scar. 
 
 j. Anterior lateral muscle scar. 
 k. Middle lateral muscle scar. 
 1. Outside lateral muscle scar, 
 p. Pedicle furrow. 
 V. Visceral area. 
 vs. Vascular sinus. 
 
 DiCELLOMUs NANUS (Meek and Hayden) (p. 573). 
 
 Figures 1 and la. Exterior and side views of ventral valves varying in outline. U. S. Nat. Mus. Cat. Nos. 51903in 
 and 51903a, respectively, 
 lb. Interior of a ventral valve. U. S. Nat. Mus. Cat. No. 51903b. 
 Ic. Natural cast of an interior of a ventral valve. U. S. Nat. Mus. Cat. No. 51903c. 
 Id. Interior of a ventral valve. U. S. Nat. Mus. Cat. No. 51903d. 
 le. Natural cast of an interior of a ventral valve. U. S. Nat. Mus. Cat. No. 51903e. 
 If. Partly exfoliated ventral valve. U. S. Nat. Mus. Cat. No. 51903f. 
 Ig and Ih. Exterior and side views of dorsal valves varying in outline. V. S. Nat. Mus. Cat. Nos. 51903g 
 
 and 51903h, respectively, 
 li. Interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 519031. 
 Ij. Natural cast of interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 51903J. 
 
 Ik. Natural cast of interior of a dorsal valve with large cardinal scars. TJ. S. Nat. Mus. Cat. No. 519031i. 
 1 1. Interior of a dorsal valve showing area. U. S. Nat. Mus. Cat. No. 519031. 
 
 The specimens represented by figures 1, la-1 are from Locality 170, Middle Cambrian limestone about 10 miles 
 south-southeast of Bald Mountain, Bighorn Mountains, Wyoming. 
 
 Figure 2. Interior of a ventral valve from Locality 355d, Upper Cambrian sandstone, Black Hills, South Dakota. 
 
 U. S. Nat. Mus. Cat. No. 1025a. Type specimen, figured by Hayden [1862, fig. 2b, p. 73] as Obolella 
 
 nana, and by Walcott [1899, PI. LX, fig. 3d] as Dicellomus nanus. 
 2a. Partly exfoliated dorsal valve associated with the shell represented by figure 2. U. S. Nat. Mus. Cat. 
 
 No. 1025b. Specimen figured by Hayden [1SG2, fig. 2a, p. 73] as Obolella nana, and by Walcott 
 
 [1899, PI. LX, fig. 3b] as Dicellomus nanus. 
 3. Exfoliated ventral valve from Locality 152a, Upper Cambrian sandstone on Dry Creek, Gallatin County, 
 
 Montana. U. S. Nat. Mus. Cat. No. 51908a. 
 3a. Natural cast of an interior of a ventral valve from Locality 170, Middle Cambrian limestone 10 miles south- 
 southeast of Bald Mountain, Bighorn Mountains, Wyoming. U. S. Nat. Mus. Cat. No. 51903n. 
 3b. Dorsal valve associated with the shell represented by figure 3a. U. S. Nat. Mu.s. Cat. No. 51903o. 
 3c and 3d. Exteriors of dorsal valves associated with the shells represented by figure 3. U. S. Nat. Mus. Cat. 
 
 Nos. 51908b and 51908c, respectively. 
 
 Dicellomus appalachia Walcott (p. 572). 
 
 Figure 4. Exterior of a ventral valve from Locality 119, Middle Cambrian limestone collected somewhere in either 
 Jefferson or Hawkins County, Tennessee. V. S. Nat. Mus. Cat. No. 51926a. 
 
 4a. Cast of interior of a ventral valve, the type specimen, from Locality 89, Middle Cambrian limestone in 
 Murphrees Valley, Blount County, Alabama. U. S. Nat. Mus. Cat. No. 51928a. 
 
 4b. Exterior of a ventral valve from Locality 90a, Middle Cambrian shales at Cedar Bluff, Cherokee County, 
 Alabama. U. S. Nat. Mus. Cat. No. 51939a. 
 
 4c. Dor.sal valve from Locality 16, Middle Cambrian limestone in Blountsville Valley, Blount County, Ala- 
 bama. U. S. Nat. Mus. Cat. No. 51937a. 
 
 4d. Partly exfoliated dorsal valve associated with the shell rei)resent«d by figure 4. L^. S. Nat. Mus. Cat. 
 No. 51926b. 
 
 4e. Partly exfoliated dorsal valve, as.sociated with the shell represented by figure 4a, .showing visceral area, 
 muscle scars, etc. U. S. Nat. Mus. Cat. No. 5192Sb. 
 
 4f. Partly exfoliated dorsal valve, from Locality 91, Middle Cambrian shales at Cedar Bluff, Cherokee 
 County, Alabama. U. S. Nat. Mus. Cat. No. 51936a. 
 
 4g. Partly exfoliated dorsal valve from Locality 103a, Middle Cambrian shale on the road from Rogersville 
 to Dodson Ford, Hawkins County, Tennessee. U. S. Nat. Mus. Cat. No. 51938a. 
 174 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. Llll 
 
 \ 
 
 cl \ 
 
 1/ 
 
 HELiOTYPE CO.. BOSTON, 
 
PLATE LIV. 
 
 175 
 
PLATE LIV. 
 
 a. Central lateral space of area. i. Transmedhin muscle scar, 
 
 a'. Outer lateral space of area. j. ^Vnt<!rior lateral muscle scar. 
 
 c. Trapezoidal area, including; central, 1. Outside lateral muscle scar. 
 
 middle lateral, and outside lateral p. Pedicle groove. 
 
 muscle scars. pc. Cast of pedicle opening, 
 
 f. Fle-vuro line of area. v. Visceral cavity, 
 
 h. Central muscle scar. vs. Main vascular sinus. 
 
 Obolei.l.v ciinoMATic.v Billings (p. 591). 
 
 Figure 1. Ventral valvo of the usual form and oullinu. U. S. Nat. Mu.s. Cat. No. 14891a. 
 
 la. Posterior view of the speciihen represented by figure lb, showing area and narrow pedicle slh. V. S. 
 Nat. Mus. Cat. No. 14891b. 
 
 lb and Ic. Outer and side view of a ventral valve that is less elongate than specimen represented by figure 1 
 (see fig. la). U. S. Nat. Mus. Cat. No. 14891b. 
 
 Id. Dorsal valve, in which the structure of the .shell is unusually well preserved. U. S. Nat. Mus. Cat. No. 
 14891c. 
 
 le. Cast in limestone of the interior of a ventral valve, showing vascular markings and muscle scars. The 
 extreme posterior portion is, unfortunately, broken away. The false pedicle furrow is too deep and 
 strqng. It is shallow in the specimen. U. S. Nat. Mus. Cat. No. 14891d. 
 
 If. Interior of a ventral valve that has a narrow thickening of the shell just in front of the area, corresponding 
 to the posterior portion of the thickened shell usually present in the ventral valve of ObokUa aassa 
 beneath the visceral area. (See figs. 2g and 2i.) Geol. Survey Canada. 
 
 Ig. Cast in limestone of the interior of a small dorsal valve. U. S. Nat. Mus. Cat. No. 14891et 
 
 Ih. Interior of a dorsal valve. The area is outlined from a specimen in the collection of the Geological Sur- 
 vey of Canada. U. S. Nat. Mus. Cat. No. 14891f. Specimen figured by Walcott [1886b, PI. XI, 
 fig. lb]. The specimens represented by figures 1 and la [AValcott, 1886b, PI. XI] are not redrawn 
 in this monograph. 
 
 li. Interior of a dorsal valve drawn from a plaster cast of a limestone cast in the collection of the Geological 
 Survey of Canada; cast in the United States National Museum (Cat. No. 14891g). Cast figured by 
 Walcott [1886b, PI. X, fig. 3]; and [1891a, PI. LXXI, fig. 3] as OboleUa circe. 
 
 The specimens represented by figiuesl, la-i are all from Locality 392a, Lower Cambrian limestone at L'Anse au 
 Loup, Straits of Belleisle, Labrador. The material in the collections of the Geological Survey of Canada includes 
 the specimens upon which Billings founded the species, but closer identification is impossible. 
 
 Obolei.la crassa (Hall) (p. 592). 
 
 [Text flg. 14, p. 299.] 
 
 Figure 2. E.xterior of a ventral valve of the usual form and outline from Locality 27, Lower Cambrian limestone in 
 
 the eastern suburb of Troy, New York. V. S. Nat. Mus. Cat. No. 15348a. 
 2a. An unusually elongate ventral valve, with the surface characters well preserved, from Locality 2b, Lower 
 
 Cambrian limestone just north of Beman Park, Troy, New York. U. S. Nat. Mus. Cat. No. 51951a. 
 2b. An unusually broad ventral valve associated wath the shell represented by figure 2a. L^. S. Nat. Mus. 
 
 Cat. No. 51951b. 
 2c and 2d. Exterior and side \-iews of a dorsal valve, associated with the shell represented by figure 2a. I". S. 
 
 Nat. Mus. Cat. No. 51951c. 
 2e. Posterior \-iew of a vPntral valve associated with the shell represented by figure 2a, showing low area and 
 
 the pedicle slit. U. S. Nat. Mus. Cat. No. 51951d. 
 2f. Section of a ventral valve as.sociated with the .shell represented by figure 2a, naturally broken near the 
 
 median line. The thickest part of the shell is over the visceral area. U. S. Nat. Mus. Cat. No. 
 
 51951e. 
 2g, 2h, and 2i. Interiors of ventral valves illustrating variation in the areas, vascular markings, and muscle 
 
 scars. Note the narrow rounded area and the shallow median furrow in figure 2h; the inner end of 
 
 the pedicle tube is shown on the specimen just beneath the inner edge of the area. Locality 2b, 
 
 Lower Cambrian limestone just north of Beman Park, Troy, New York. U. S. Nat. Mus. Cat. Nos. 
 
 51951f, 51951g, and 51951h, respectively. 
 176 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LIV 
 
 FRANCES WIESER DEL. 
 
 HCLtuTi/PE CO BOSTON 
 
PLATE LIV. 177 
 
 Obolella crassa (Hall) — Continued. 
 
 Figure 2j. Interior of ventral valve from Locality 29a, Lower Cambrian limestone at Sehodaek, Rensselaer County, 
 New York. U. S. Nat. Mus. Cat. No. 51952a. 
 
 2k. Interior of a dorsal valve associated with the specimen represented by figiire 2a. V. S. Nat. Mus. Cat. 
 No. 519511. 
 
 2 L Cast in limestone of the interior of a dorsal valve from Locality 27, Lower Cambrian limcslone in the 
 eastern suburb of Tro>', New York. The exact position of the anterior lateral mu.sde scars in figure 
 2 1 is more or less uncertain and the line from (i) indicating the transmedian scar should unite wilh 
 that from (1) as in figure 2 1. V. S. Nat. Mus. Cat. No. 15347a. Specimen figured by WalcoU [1886b, 
 PL X, fig. Ic]. The other specimens illu.strated [Walcott, 1886b] are not redrawn in this monograph. 
 
 2m. Interior of a dorsal valve associated with the specimen represented by figure 2a. The other specimens 
 were used to draw in the details of the area. U. S. Nat. Mus. Cat. No. 51951J. 
 
 2n. Cast of the interior of a ventral valve associated with the shell represented by figure 2a. U. S. Nat. Mus. 
 Cat. No. 51951k. 
 
 Obolella minor (Walcott) (p. 596). 
 
 Figure 3. Exterior of a ventral valve. U. S. Nat. Mus. Cat. No. 24628c. 
 
 3a. Cast of the interior of a ventral valve, the type specimen, showing area and cast of pedicle groove. U. S. 
 
 Nat. Mus. Cat. No. 24628a. 
 3b. Cast of interior of ventral valve. U. S. Nat. Mus. Cat. No. 24628d. 
 3c. Exterior of dorsal valve. U. S. Nat. Mus. Cat. No. 24628b. 
 3d. Cast of interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 24628e. 
 
 The specimens represented are all from Locality 32, Lower Cambrian sandstone, Stis.sing Mountain, Dutchess 
 County, New York. The figures (3, 3a-d) are copied from Walcott [lS91a, PI. LXXII, figs. 4a, 4d, 4, 4b, and 4c, 
 respectively]. They were then labeled " Camarella f minnr." 
 62667°— VOL 51, pt 2—12 12 
 
PLATE LV. 
 
 179 
 
PLATE LV. 
 
 a. Central lateral space o( area, 
 i. Transmedian muscle scar, 
 j. Anterior lateral muscle scar. 
 1. Outside lateral scar. 
 p. Pedicle groove. 
 
 pc. Cast of pedicle opening. 
 
 s. Median septum. 
 
 V. Visceral cavity, 
 vs. Main vascular sinus. 
 
 .\. Heart-shaped cavity 
 
 Ic. 
 
 Id. 
 
 le. 
 
 Obolella atlantica Walcolt (p. 589). 
 
 (Text fig. 51, p. aiil.l 
 
 Figure 1. Exterior of an unusually convex, elongate \entral valve. Locality So, Lower Cambrian siliceous shale, 
 Smith Sound, Trinity Bay, Newfoundland. U. S. Nat. Mus. Cat. No. 51948a. 
 
 la. Cast in siliceous shale of the exterior of a ventral valve, showing surface characters of the shell. Same 
 locality as specimen represented by figure 1. V. S. Nat. Mus. Cat. No. 51948b. 
 
 lb. Exterior of a small ventral ? valve. Locality 41a, Lower Cambrian limestone beneath Topsail Head, 
 Conception Bay, Newfoundland. U. S. Nat. Mus. Cat. No. 56957a. 
 Exterior of small dorsal valve, associated with specimen represented by figure ll>. U. S. Nat. Mus. Cat. 
 
 No. .5G957b. 
 A slightly distorted dorsal valve from Locality 5o, Lower Cambrian siliceous shale, Smith Sound, New- 
 foundland. U. S. Nat. Mus. Cat. No. 5194Sc. 
 Interior of a ventral valve associated with the shell represented by figiu-e Id. The pedicle furrow is too 
 strong in the figure. On the specimen it is indicated by a slightly depressed line on each side of 
 what is usually the pedicle fuiTow. This specimen i.s also figured in a slightly different position in 
 text figure 51, p. 590. U. S. Nat. Mus. Cat. No. 51948d. 
 
 If and Ig. Casts of the interior of ventral valves associated with the shell represented by figure Id. U. S. 
 Nat. Mus. Cat. Nos. 51948e and 51948f, respectively. 
 
 Ih. Top and side view of cast of the interior of a ventral valve, the type specimen, from Locality 41, Lower 
 Cambrian decomposed limestone, from Manuels Brook, Conception Bay, Newfoundland. L^. S. Nat. 
 Mus. Cat. No. lS322a. • 
 
 li. Cast of the interior of a dorsal valve, associated with specimen represented by figure Ih. U. S. Nat. Mus. 
 Cat. No. 18322b. 
 
 Obolei.la (Glyptias) favosa (Linnarsson) (p. 600). 
 
 Figure 2. Exterior and side view of ventral valve. U. S. Nat. Mus. Cat. No. 3.52G4a. 
 2a. Exterior and side view of dorsal valve. U. S. Nat. Mus. Cat. No. 3.5264b. 
 
 2b. Cast of the interior of ventral valve that retains a portion of the shell. U. S. Nat. Mus. Cat. No. 35264c. 
 2c. Cast of the interior of small dorsal valve. V. S. Nat. Mus. Cat. No. 3.5264d. 
 2d. Outer surface of shell greatly enlarged. U. S. Nat. Mus. Cat. No. 35264e. 
 
 The specimens represented b\- figures 2. 2a-d are from Locality 309c, Lower Cambrian sandstone at Billingen, 
 Province of Skaraborg, Sweden. 
 
 Obolella mobergi Walcott (p. 597). 
 
 Figures 3 and 3a. Exterior and side view of ventral valve, drawn fmm a cast taken in a natural mold in sandstone. 
 
 Original in the collection of the Geological Mu.sotini. Lund, Sweden; cast in the United States National 
 
 Mu.seum (Cat. No, 352Gla). 
 3b. Posterior view of specimen represented liy figure 3, showing area and cast of pedicle slit. 
 3c. Ca.st in fine sandstone of interior of ventral valve, the type specimen. U. S. Nat. Mus. Cat. No. 35261b. 
 3d. Enlargement of a natural cast of a portion of the outer surface. U. S. Nat. Mus. Cat, No. 3.5261c, 
 3e. Cast of the interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 35261d. 
 3f. Cast of the interior of a dorsal valve. V. S. Nat. Mua. Cat. No. 35261e. 
 
 The specimens represented are all from Localily 321s, Lower Cambrian sandstone at Sularp, near Lund. Province 
 of Malmohus, Sweden. 
 180 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LV 
 
 f«ANCC8 WIESES ou. 
 
 HEUOTVPE CO.. BOSTON 
 
PLATE LV. 181 
 
 Obolella? i.iNDSTROMi Walcott (p. 596). 
 
 Figure 4. Exterior of a vciilral valve, the type specimen, from Locality 321v, Lower Cambrian sandstone at 
 Bjorkelunda, Province of Christianstad, Sweden. The specimen from which this (i^iire was drawn 
 can not be located. A record of the locality wn.i, however, preserved. 
 4a. Cast of the interior of dor.sal valve, from Locality 321s, Lower Cambrian sandstone at Sularp, near Lund, 
 Province of Malmohus, Sweden. U. S. Nat. Mu.s. Cat. No. 3.5263a. 
 
 Obolella crassa elongata Walcott (p. 595). 
 
 Figure 5. Ventral valve, the type specimen from Locality 319b, Lower Cambrian lime.stone at St. Simon, Quebec, 
 Canada. U. S. Nat. Mus. Cat. No. 14691a. 
 5a. Dorsal valve a.ssociated with specimen represented by figure 5. U. S. Nat. Mus. Cat. No. 14691b. 
 
 Obolella asiatica Walcott (p. 588). 
 
 Figure fi. Exterior of ventral valve, the type specimen. U. S. Nat. Mus. Cat. No. .52525a. 
 6a. Exterior of dor.sal valve. U. S. Nat. Mus. Cat. No. 52.525b. 
 
 The specimens represented are both from Locality C32', Lower Camlirian limestone bnwlder 1 mile south of 
 Chonpinghien, on Nankiang River, Shensi, China. 
 
 Obolella wirrialpensis Etlieridge (p. 599). 
 
 Figures 7 and 7'. Top and side views of ventral valve. University of Adelaide, South Australia. 
 
 7a. Exterior of dorsal valve marked by strong concentric ridges. IT. S. Nat. Mus. Cat. No. 51963a. 
 7b. Dorsal valve. Universitv of Adelaide, South Australia. Type specimen, figured by Etheridge [1905, 
 PI. XXV, fig. 2]. 
 
 The specimens represented by figures 7, 7a-b are all from Locality 315d, Lower? Cambrian limestone near 
 Wirrialpa, Flinders Range, South Australia. 
 
PLATE LVI. 
 
 183 
 
PLATE LVI. 
 
 cl. Cardinal scars. s. Median septum. 
 
 F'. Cast of toraminal tube. ' v. Visceral area, 
 
 fa. False area. vs. Vascular sinuses, 
 
 j. Anterior lateral muscle scar. x'. Cast of risceral cavity. 
 
 AcROTHELE CORIACEA Linnarssoii (p. 642). 
 
 Figure 1. Top and back view of ventral valve from Locality 334f, Middle Cambrian limestone on Bomholm Island, 
 
 Denmark. U. S. Nat. Mus. Cat. No. .519S3a. 
 la. Interior of a ventral valve from Locality 320f, Middle Cambrian limestone at Andrarum, Province of 
 
 Christianstad, Sweden. U. S. Nat. iltis. Cat. No. 1820Sa. 
 lb. Cast of interior of a ventral valve associated with the specimen represented by figure la. V. S. Nat. 
 
 Mus. Cat. No. 18208b. 
 Ic. Cast of interior of a ventral valve associated with the specimen represented by figure la. U. S. Nat. 
 
 Mus. Cat. No. 18208e. 
 Id and le. Interiors of dorsal valves associated with the specinien represented by figure la. U. S. Nat. Mus. 
 
 Cat. Nos. 1S20SC and 18208d, respectively. 
 If. Cast of interior of a dorsal valve associated with the specimen represented by figure la. U. S. Nat. Mus. 
 
 Cat. No. 1820Sf. 
 Is;. Enlargement of the surface of a specimen associated with the shell represented by figure 1. U. S. Nat. 
 
 Mus. Cat. No. 519S3b. 
 Ih and Ih'. Top and side views of a spiall ventral valve from Locality 8w, Middle Cambrian limestones at 
 
 Andrarum, Province of Christianstad, Sweden, showing the small node on each side of the apex. 
 
 U. S. Nat. Mus. Cat. No. 5I97Sa. 
 li. Top and back view of a very small ventral valve associated with the shell represented by figure Ih, showing 
 
 a central posterior node, and a small noeje on each side of the apex. V . S. Nat. Mus. Cat. No. 51978b. 
 
 AcROTHELE (Redlichella) graxvlata (Linnarssoii) (p. 663). 
 
 Figure 2. Top and side views of exterior of a ventral valve from Locality 8z, Middle Cambrian limestones of the 
 
 Parado.ridts celandiais zone at Corgholm. Oeland Island, Sweden. V . S. Nat. Mus. Cat. No. 51991a. 
 2a. Interior of a ventral valve from Locality 310o, Middle Cambrian limestones of the Paradoxides tcssini zone 
 
 at Borgholm, Oeland Island, Sweden. IT. S. Nat. Mus. Cat. No. 56643a. 
 2b. Cast of the interior of a ventral valve from Locality 309f, Middle Cambrian shale at Borgholm, Oeland 
 
 Island, Sweden. U. S. Nat. Mus. Cat. No. 23S97a. 
 2c. Interior of a ventral valve associated with the shell represented by figure 2, showing visceral area. U. S. 
 
 Nat. Mus. Cat. No. 51991b. 
 2d. Top and side views of exterior of a dorsal valve associated with the shell represented by figure 2. V. S. 
 
 Nat. Mus. Cat. No. 51991c. 
 2e. Interior of a dorsal valve associated with the shell represented by figure 2. T. S. Nat. Mus. Cat. No. 
 
 51991d. 
 2f. Exterior of a dorsal valve associated with the shell represented by figure 2b, showing elongate tubercles 
 
 at the apex. U. S. Nat. Mus. Cat. No. 23S97b. 
 2g. Enlargement of the surface of the specimen represented by figure 2f. L'. S. Nat. Mus. Cat. No. 23S97b. 
 2h. Exterior of a dorsal valve from Locality 320b, Middle Cambrian limestones at Gudhem, Pro\-ince of 
 
 Skaraborg, Sweden. U. S. Nat. Mus. Cat. No. 51992a. 
 2i. Cast of an interior of a ventral valve associated with the dorsal valve represented by figure 2h, showing 
 
 the cast of the visceral area (v), the expanded interior opening of the foraminal tube (F'), a'"' niain 
 
 vascular sinuses (vs). U. S. Nat. Mus. Cat. No. .51992b. 
 2], Partly exfoliated ventral valve from Locality 309f, Middle Cambrian shale at Borgholm, Oeland Island, 
 
 Sweden, showing the main vascular sinuses and branches. U. S. Nat. Mus. Cat. No. 23897c. 
 2k. Fragment of the interior of a ventral valve associated with the shells represented by figures 2h and 2i, 
 
 greatly enlarged so as to show the outline of the visceral area. U. S. Nat. Mus. Cat. No. 51992e. 
 184 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LVI 
 
 r 
 
 ,ij 
 
 ;'/ 
 
 i:;a 
 
 f2SEi??^SE?i»affiiSg3i31 
 
 
 R .i^, 
 
 I 
 
 M 
 
 « 
 
 li 
 
 z" 
 
 ^ 
 
 FRANCES WIES£R DEL. 
 
 HELIOTYPE CO.. BOSTON. 
 
PLATE LVI. 185 
 
 AcROTHELE (Redlichella) GRANULArA (Liiuiiirsson) — Continued. 
 
 Figure 21. fast of the interior of a dorsal valve associated with the 8))ecimen represented by figure 2j. U. R. Nat. 
 Mus. Cat. No. 23897d. 
 2m and 2n. Side and posterior views of a shell in whieh the two valves are united, as80ciate<l with the shell 
 represented by fi<;iire 2. V. S. Nat. Mus, Cat. No. 51991e. 
 
 AcROTHELE INTERMEDIA Linnarsson (p. 646). 
 
 Figures 3 and 3a. Ventral valve, the type specimen, with side outline, X-1. Copied from l.innar.sson [1879, PI. Ill, 
 
 figs. 40 and 41]. 
 3b. Interior of a ventral valve, showing main vascular canals and branches, X-i. Copied from Linnarsson 
 
 [1879, PI. Ill, fig. 43]. 
 3c. Cast of the interior of a ventral valve. Copied from Linnarsson [1879, PI. Ill, fig. 42|. 
 3d. Cast of the interior of a broken dorsal valve. Copied from Linnar.'sson [1879, PI. Ill, fig. 44]. 
 
 The specimens represented by figures 3, 3a-c are from Locality 320k, Middle Cambrian limestones of the Coro- 
 nnlux zone at Kiviks Esperod, Province of Malmohus; the specimen represented by figure 3d is from Locality 3201, 
 the same horizon, at Andrarum, Province of Christianstad; both in Sweden. ^ 
 
PLATE LVII. 
 
 187 
 
PLATE LVII. 
 
 cl. Cardinal scare. «• Median septum. 
 
 F. Foramen. v. Visceral area. 
 
 F'. Cast of pedicle tube. vs. Vascular sinus. 
 
 AcROTHELE BOHEMiCA (Barraiule) (p. 639). 
 
 Figures 1 and 1'. Top and side views of ventral valve, the type specimen, from Locality 345c, Middle Cambrian 
 
 shales at Mlestbitz, Bohemia. Copied from Barrande [1879b, PI. CII, figs, vii: lA and IB], where 
 
 they are labeled Obolus ? hohcmims. 
 la and la'. Top and side ^iews of a dorsal valve associated with the ventral valve represented by figure 1. 
 
 Copied from Barrande [1879b, PI. CII, figs, vii: 2A and 2B], where they are labeled OhoUts 1 hohimicus. 
 lb. Ventral valve from Locality 345, Middle Cambrian shales on the DlouhA Hora, above the brook of Sbirov, 
 
 near Skrej, Bohemia. Copied from Pompeckj [189(Jb, PI. XIV, fig. 8b]. 
 Ic. Dorsal valve from the locality represented by figure lb. Copied from Pompeckj [1896b, PI. XIV, 
 
 fig. lib]. 
 Id. Interior of dorsal valve from the locality represented by figure lb. Copied from Pompeckj [1896b, PI. 
 
 XIV, fig. 10b]. 
 
 AcROTHELE siACX.'LATA (Salter) (p. 647). 
 
 [PI. LVIII, flg.2.] 
 
 Figure 2. Exterior of dor.sal valve. 
 2a. Extericir of dorsal valve. 
 2b. Cast of the interior of a dorsal valve, the type specimen. 
 
 Figures 2, 2a-b are copied from Davidson [1868, PI. XVI. figs. 1-.3]; the same figures being copied by Davidson in 
 his later work [1871, PI. L. tig.s. 18. 19, and 21]. Davidson states that the specimens are from Porth-y-rhaw, St. Davids, 
 and from Gwjaifvaiydd and Camlaii. North Wales. 
 
 AcROTHELE BELLAPUNCTATA Wakott (p. 636). 
 
 Figure 3. Exterior of partly exfoliated ventral valve, the type specimen. U. S. Nat. Mus. Cat. No. 51972a. 
 Copied from Walcott [1908d, PI. VIII, fig. 9]. 
 3a. Exterior of partly exfoliated dorsal valve. U. S. Nat. Mus. Cat. No. 51972b. 
 
 3b. Siu-face of outer layer enlarged 15 diameters. V. S. Nat. Mus. Cat. No. 51972c. A portion of the surface 
 * represented by figure 3b was illustrated by Walcott [1908d, PI. VIII, fig. 9'] as the surface of the 
 
 specimen represented by figui-e 3; it is, however, taken from another specimen. 
 The specimens represented are all from Locality 8v, Lower Cambrian shales at Eingsaker. near Lake Mjosen, 
 Province of Hedemarken, Norway. 
 
 BOTSFORDIA GRANO.ATA (RcclUcll) (p. 605). 
 
 Figure 4. Cast of exterior of an almost perfect specimen of the transversely oval form of the ventral valve. U. S. 
 Nat. Mus. Cat. No. 52046s. 
 
 4a. Exterior of a longitudinally elongate oval form of the ventral vahe. U. S. Nat. ilus. Cat. No. 52046a. 
 
 4b. Exterior of a transversely oval dorsal valve, preserving the two small .sharp tubercles at the apex. U. S. 
 Nat. Mus. Cat. No. 52046b. 
 
 4c. Posterior portion of a ventral valve, showing the pedicle aperture. U. S. Nat. Mus. Cat. No. 5204Gc. 
 
 4d. Posterior portion of a ventral valve, showing a crescentiform tubercle on each side of and a small tubercle 
 just back of the depression at the apex; the pedicle aperture is just back of the posterior tubercle 
 and in fact appears to come up through it. L'. S. Nat. Mus. Cat. No. 52040d. 
 
 4e. Exterior view of elongate form of dorsal valve. V. S. Nat. Mus. Cat. No. 52046e. 
 
 4f and 4f'. Exterior and side view of a ventral valve intermediate in outline between the specimens repre- 
 sented by figures 4 and 4a. U. S. Nat. Mus. Cat. No. 52046f. 
 
 4g. Cast of interior of ventral valve. U. S. Nat. Mus. Cat. No. 52046g. 
 188 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LVIl 
 
 FRANCES WIESER DEL. 
 
 HELIOTVPE CO.. BOSTON 
 
PLATE LVII. 189 
 
 BoTSFORDiA GRANULATA (Redlicli) — Continued. 
 
 Figure 4h. Partly exfoliated ventral valve, showing the impression of the main vascular sinuses on the inner layers 
 of the shell. U. S. Nat. Mus. Cat. No. 52040h. 
 4i. Cast of interior of a small ventral valve. U. S. Nat. Mus. Cat. No. 52046i. 
 4j. Cast of interior of a dorsal valve. U. S. Nat. Mus. Cat. No. .52046J. 
 4k. Interior of a small dorsal valve. U. S. Nat. Mus. Cat. No. 52046k. 
 4 1. Partly exfoliated dorsal valve. U. S. Nat. Mus. Cat. No. 52046 1. 
 4m. Interior of a dorsal valve. U. S. Nat. Mus. Cat. No. .52046m. 
 4n and 4o. Exteriors of dorsal valves, showing variation in outline, as compared with figure 4b, and in small 
 
 , tubercles near the apex. U . S. Nat. Mus. Cat. Nos. 52046n and 52046o, respectively. 
 4p. Interior of a ventral valve. U. S. Nat. Mus. Cat. No. 52046p. 
 4q. Exterior of one of the largest ventral valves. U. S. Nat. Mus. Cat. No. 52046q. 
 4r. Enlargement of surface to show granulations. U. S. Nat. Mus. Cat. No. 52040r. 
 
 The specimens represented are all from Locality 15r, Middle Cambrian shale at Khussak, Salt Range, India. 
 
 ACROTHELE QtTADRILINEATA Pompeckj (p. 655). 
 
 Figure 5. Top and side views of the type specimen, a ventral val\-e, from Locality 345d, Middle Cambrian shales 
 at Skrej, Bohemia. Copied from Pompeckj [1896b, PI. XIV, figs. 6b and 6c]. 
 
 AcROTHELE PRiMiEVA (de Verncuil and Barrande) (p. 654). 
 
 Figures 6 and 0'. Top and side views of the type specimen, a ventral valve, from Locality 350, Middle Cambrian 
 limestone near .Vdrados, Cantabrian Mountains, Pro^^nce of Leon, Spain. Cojjied from de Verneuil 
 and Barrande's figures [1860, PL VIII, figs, 2 and 2a] of Discina (Orhict'Un primxva. 
 
 BoTSFORDIA? BARRANDEI Walcott (p. 602). 
 
 Figure T. Dorsal view of the type specimen, showing apex of ventral valve, from Locality 350, Middle Camljrian 
 limestone near Adrados, Cantabrian Mountains, Province of Leon, Spain. 
 7a and 7b. Posterior and side views of the specimen represented by figure 7. 
 
 Figures 7, 7a-b are copied from de Verneuil and Barrande's figures [1860, PI. VIII, figs. 5, 5a-b] of " Brachiopode, 
 nouv. gen." 
 
PLATE LVIII. 
 
 191 
 
PLATE LVIII. 
 
 cl. Cardinal soars. h. Central muscle scar. 
 
 F. Foramen. s. Median septum. 
 
 F'. Cast of foraniiiKil tube. v. Visceral area, 
 
 fa. False area. vs. Vascular sinuses. 
 
 ACROTHKLE PRETIOSA (Billings) ()). ()r)2) . 
 
 Figures 1 and la. Exteriors of crushed and sliyluly dis^toricil \cniral valves. L'. S. Nat. Mus. Cat. Nos. 52004a and 
 
 52004b, respectively. 
 lb. Partly exfoliated and compressed ventral valve. I'. S. Na(. Miis. Cat. No. 52004c. 
 Ic. Exterior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52004d. 
 Id. Cast of the interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52004e. 
 le. Interior of dorsal valve. V. S. Nat. Mus. Cat. No. 52004f. 
 If. Cast of interior of a dorsal valve, showing median septum e.xlending well toward Ihe front margin. U. S. 
 
 Nat. Mus. Cat. No. .52004g. 
 Ig. Interior of dorsal valve. U. S. Nat. Mus. Cat. No. .')2004h. 
 
 The specimens represented are all from Locality 220a, ( )rdovi<-ian shales at the Grand Trunk railroad bridge over 
 Chaudiere River, Quebec, Canada. 
 
 ACROTHELE MACUL.\TA (.Saltei-) (p. 647). 
 (PI. LVII, figs. 2, 2a-b.] 
 
 Figure 2. Exterior of distorted and com])ressed ventral valve from Locality 3181i, Middle Cambrian Menevian shales 
 of St. Davids, South Wales. U. S. Nat. Mus. Cat. No. 51993a. 
 
 AcROTHELE DECiPiEXs Walcott (p. 644). 
 
 Figure 3. Exterior of ventral valve with side and transverse outline. L'. S. Nat. Mus. Cat. No. ^6435b. 
 
 3a. Partly exfoliated ventral valve, the type specimen, with the rim of the foraminal aperture broken off. 
 
 U. S. Nat. Mus. Cat. No. 26435a. Specimen figured by Walcott [lS97b. PI. LX, fig. 2], 
 3b. Exterior of dorsal valve. U. S. Nat. Mus. Cat. No. 2()43oc. 
 3c. Interior of a compressed dofsal valve. U. S. Nat. Mus. Cat. No. 26435d. 
 3d. Cast of an interior of a distorted dorsal valve. IT. S. Nat. Mus. Cat. No. 26435e. 
 
 The specimens represented are all from Locality 50, Lower Cambrian .shale, 1.125 miles north of Stoner, York 
 County, Pennsylvania. 
 
 ACROTHELE NITIDA (Fdl'll) (p. 650). 
 
 Figure 4. Exterior of the type specimen, a dorsal vahe, from Locality 27, Lower Cambrian limestone in the eastern 
 suburb of Troy, New York. U. S. Nat. Mus. Cat. No. 15353a. Specimen figured jWaU-ott, 1886b, 
 PI. XI, fig. 2] as Obolella nitida. 
 4a. Interior of dorsal valve associated with the specimen represented by figure 4. U. S. Nat. Mus. Cat. No. 
 15353b. 
 
 ACROTIIELE BELLULA Walcott (p. 637). 
 
 Figure 5. Exterior of a small ventral valve, the typo specimen, from Locality 90x, Middle Cambrian siliceous nodules 
 in Coosa Valley, Cherokee County, Alabama. U. S. Nat. Mus. Cat. No. 26436a. Another specimen 
 (Cat. No. 26436b) was used in restoring certain portions of this figure. Copied from Walcott [1897b, 
 PI. LX, fig. 4]. 
 
 5a. Cast of the interior of a slightly distorted ventral valve from Locality 94x, Middle Cambrian shale near 
 Givens Mill, Cowan Creek, Cherokee County, Alabama. A porti(m of the shell is jireserved near 
 the apex. U. S. Nat. Mus. Cat. No. 56602a." Copied from Walcott [1897b, PI. LX, fig. 4a]. 
 
 5b. Natural cast of the foraminal tube of a specimen associated with the shell represented by figure 5. 
 V. S. Nat. Mus. Cat. No. 26436c. 
 192 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LVIII 
 
 &lm 
 
 FRANCES WieSER DEL. 
 
 HELIOTYPE CO.. BOSTON. 
 
PLATE LVIIl. 193 
 
 AcROTHELE BELLULA Walcott — Continued. 
 
 Figure 5c. Enlargement of the cast of the interior of a ventral valve associated with the shell represented by figure 5. 
 
 IT. S. Nat. Mus. Cat. No. 2fi43fid. Copied from Walcott [1897b, PI. LX, fig. 4b]. In thi.s figure the 
 
 line indicating the cardinal scar is extended a little too far. It should have stopped before reaching 
 
 the depression. 
 5d. Cast of the posterior ])ortiou of the interior of a ventral valve associated with the shell represented by 
 
 figure 5. U. S. Nat. Mus. Cat. No. 26436e. In this figure the line indicating the cardinal scar is 
 
 extended a little too far. It should have stopped before reaching the depression. 
 5e. Cast of the interior of a small ventral valve associated with the shell represented by figure 5, showing 
 
 vascular sinuses. U. S. Nat. Mus. Cat. No. 26436f. 
 5f . Interior of a dorsal valve drawn from a cast of the specimen represented by figure 5g, showing the area, 
 
 median septum, and diverging vascular sinuses. U. S. Nat. Mus. Cat. No, 26436g. Another specimen 
 
 (Cat. No. 26436h) was used in restoring certain portions of this figure and of figure 5g. Copied from 
 
 Walcott [lS97b, PI. LX, fig. 4c]. 
 5g. Natural cast of the interior of a dorsal valve from Locality 90x, Middle Cambrian siliceous nodules, Coosa 
 
 Valley, Cherokee County, Alabama. A cast of this specimen is represented by figure of. U. S. Nat. 
 
 Mus. Cat. No. 26436g. Copied from Walcott [1897b, PI. LX, fig. 4d]. 
 5h. Cast in shale of the interior of a dorsal valve from Locality 94x, Middle Cambrian shales near Givens Mill, 
 
 Cowan Creek, Cherokee County, Alabama. The cardinal muscle scar is drawn too far away from 
 
 the median line. It should be about the length of the scar from the median line. V. S. Nat. Mub. 
 
 (Cat. No. .56fi02b. Cojuod from Walcott [1897b, PI. LX, fig. 4e]. 
 
 AcROTHELE BERGERONI Walcott (p. 63S). 
 
 Figures 6 and 6a. Exteriors of compressed and slightly distorted ventral valves. U. S. Nat. Mus. Cat. Nog. 51975b 
 and 51975c, respectively. 
 6b. Cast of the interior of a compressed and distorted ventral valve. U. S. Nat. Mus. Cat. No. 51975d. 
 6c. Cast of the interior of a dorsal valve, the type specimen, flattened in the shale. U. S. Nat. Mus. Cat. 
 No. 51975a. Copied from ^Valcott [1908d, PI. VIII, fig. 11]. 
 
 The specimens represented are all from Locality 342, Middle Cambrian shales in Montague Noire, Coulouma, 
 H6rault, France. 
 62667°— VOL 51, pt 2—12 13 
 
PLATE LIX. 
 
 195 
 
PLATE LIX. 
 
 a. Area. s. Median septum. 
 
 cI. Cardinal scars. v. \'isci>ral area. 
 
 F'. Cast of foraminal tube. vs. Vascular sinus. 
 
 BOTSFORDI.V C.ELATA (Hall) (p. 60.3). 
 [H. LIX, figs. 3, 3a-b.] 
 
 FiociiE 1. Partly exfoliated, broken ventral valve from Locality 2o, Lower Cambrian limestone bowlders at entrance 
 
 to Kic Harbor, Quebec, Canada. U. S. Nat. Mus. Cat. No. 3.5L'.59a. 
 la. Fragment of a large ventral valve from Locality 2b, Lower Cambrian limestone nnrlh ni IScman Park, near 
 
 Troy, New York. U. S. Nat. Mus. Cat. No. 52040a. 
 lb. Top, side, and back views of a ventral valve associated with Ihe shell represented by figure la, showing 
 
 the foraminal aperture. U. S. Nat. Mus. Cat. No. 52040b. 
 Ic. Broad form of ventral valve from Locality 27, Lower Cambrian limestone in the eastern suburb of Tn>y, 
 
 New York. U. S. Nat. Mus. Cat. No. 15325a. Specimen figured [Walcott, 1886b, I'l. VII, (ig. IbJ as 
 
 LinguhUa cxlata. 
 Id. Small ventral valve associated with the shell represented by figure 1. U. S. Nat. Mus. Cat. No. 35259b. 
 le. Cast of part of the interior of a ventral valve from Locality 2p, Lower Cambrian limestone a little west of 
 
 Bic, Quebec, Canada. U. S. Nat. Mus. Cat. No. 56874a. 
 If. Interior of a small ventral valve from Locality 36a, Lower Cambrian limestone on Bald Mountain, Washing- 
 ton County, New York. U. S. Nat. Mus. Cat. No. 52037a. 
 Ig. Fragment of the interior of a ventral valve from Locality 29a, Lower Cambrian limestone at Schodack, 
 
 Rensselaer County, New York. V. S. Nat. Mus. Cat. No. "l.5323a. 
 Ih. Enlargement of a portion of the exterior siu-face of a ventral \alve associated with the specimen represented 
 
 by figure 1. U. S. Nat. Mus. Cat. No. 35259c. 
 li. Partly exfoliated dorsal valve associated with the specimen represented by figure la. U. S. Nat. Mus. 
 
 Cat. No. 52040c. 
 Ij. Posterior portion of a dorsal valve associated with the specimen represented by figure la. U. S. Nat. Mus. 
 
 Cat. No. 52040d. 
 Ik. Cast of the posterior portion of the interior of a dorsal \alve associated with specimen represented by figure 
 
 la. U. S. Nat. Mus. Cat. No. 52040e. 
 
 II. Partly exfoliated dorsal valve from Locality 35, Lower Cambrian limestone 1.5 miles north of Bald Moun- 
 
 tain, Washington County, New York. V. S. Nat. Mus. Cat. No. 17457a. 
 Im. Partly exfoliated dorsal valve associated with the specimen represented by figure la, showing cast of llr,' 
 
 median septum and main vascular sinuses. U. S. Nat. Mus. Cat. No. 52040f. 
 In. Fragment of a cast of the interior of a dorsal valve. The true outline of this specimen and the locality arc 
 
 unknown. Am. Mus. Nat. Hist., New York. 
 
 III. Enlargement of surface of a dorsal valve associated with the specimen represented by figure Ic. U. S. 
 
 Nat. Mus. Cat. No. 15325b. Specimen figured [Walcott, 188Gb, PI. VII, fig. Id] as Llngiilrlla cselata. 
 Ip and Ip'. Thin section of limestone containing many shells of the species from Locality 2b, Lower Cambrian 
 
 limestone north of Beman Park, Troy, New York. V. S. Nat. Mus. Cat. No. 52040g. 
 Iq. Exfoliated ventral valve showing cast of pedicle opening and visceral ca\-ity, from Locality 29a, Lower 
 
 Cambrian limestone at Schodack, Rensselaer County, New York. L'. S. Nat. Mus. Cat. No. 15323b. 
 
 MicKWiTziA MONiLiFERA (Linnarssoii) (p. 3.30). 
 
 [I'l. \l. rigs. 1, la-p.) 
 
 Figure 2. Top and side views of the posterior portion of a ventral valve from Locality 396v, Lower Cambrian sandstone 
 below the cement factory on Kunda Bmok, (iiivernmciU of Esthonia, Russia. U. S. Nat. Mus. Cat. 
 No. 61522a. 
 
 BOTSFOKDIA C'.KI.ATA (Hall) (]). 603). 
 |1'1. LI.K.figs. 1, la-q.l 
 
 Figure 3 and 3a. Top and back views of a ventral valve from Locality 39a, Lower Cambrian limestone north of Easton 
 Station, Washington County, New York. I'. S. Nat. Mus. Cat. No. 52039a. 
 3b. Interior of a dorsal valve from Locality 38, Lower Cambrian limestone 3 miles west of South Granville, 
 Washington County, New York. U. S. Nat. Mus. Cat. No. 5203Sa. 
 196 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. UX 
 
 .s^;?'^:^ 
 
 ■1' 
 
 PE CO aosroN 
 
PLATE LIX. 197 
 
 ACROTHELE YORKENSIS Walcott (p. 661). 
 
 Figure 4. Extcrinr of tho type specimen, a distorted, broken ventral valve, from Locality 48d, Middle Cambrian shales 
 iu railroad cut at York, Pennsylvania. U. S. Nat. Mils. Cat. No. 520.31a. Copied from Walcott 
 [190Sd, PI. IX, fig. 10]. 
 4a and 4b. Compressed, exfoliated donsal valves associated with the .specimen represented by figure 4. U. S. 
 Nat. Mus. Cat. Nos. 520:Ub and .52031c, respectively. 
 
 AcROTHELE PANDERI Walcott (p. 651). 
 
 FiGUnE.s 5 and 5'. Exterior and side views of a ventral valve, the type specimen, from Locality 4v, Lower Cambrian 
 
 shales on Gordon Creek, Ovando quadrangle, Montana. U. S. Nat. Mus. Cat. No. 52003a. 
 5a. E.xterior of ventral valve as.sociated with the shell represented by figure 4. U. S. Nat. Mus. Cat. No. 
 
 52003b. 
 5b. Exterior of ventral valve from Locality 6j, Lower Cambrian shales 6 miles west-northwest of Scapegoat 
 
 Mountain, Coopers Lake cjuadrangle, Montana. V. S. Nat. Mus. Cat. No. 52002a. 
 5c. Partly exfoliated dorsal valve associated with the shell represented by figure 5b. U. S. Nat. Mus. Cat. 
 
 No. 52002b. 
 
PLATE LX. 
 
 199 
 
PLATE LX. 
 
 cl. Cardinal sear. ]. Anterior ialeral muscle scar. 
 
 fa. Faise area. s. Median septum. 
 
 h. Centrai muscle scar. vs. Vascular sinus. 
 
 A.CKOTHELE suBsiDUA (White) (p. 656). 
 
 [PI. LX, fig. 8.) 
 
 Figure 1. Interior of a ventral valve from Locality 4 (?), drift pieces believed to be from the 'WTieeler formation, 
 
 near Antelope Springs, House Range, Utah, showing outline of false area. U. S. Nat. Mus. Cat. Xo. 
 
 15435a. Type specimen, figured by ^Vhite [1877, PI. I, fig. 3a] as Acrotreta f subsidua. 
 la. Exterior of ventral valve from Locality 163. Middle Cambrian Spence shale member of Ute limestone, 
 
 Spence Gulch, 15 miles west of Montpelier, Idaho. U. S. Nat. Mus. Cat. \o. 5201.5a. 
 lb. Exterior of an exfoliated ventral valve associated with the specimen represented by figure la, showing 
 
 several radiating ribs. U. S. Nat. Mus. Cat. No. 52015b. 
 Ic. Exterior of a small ventral valve associated with tlie specimen represented by figure la. U. S. Nat. Mus. 
 
 Cat. No. 52015c. 
 Id. Almost perfect ventral valve in the Langston limestone. Locality 5b, 2 miles southeast of Malade, Idaho. 
 
 U. S. Nat. Mus. Cat. No. 52014a. 
 le. A cast of the interior of a ventral valve associated with llie specimen represented by figure Id. U. S. Nat. 
 
 Mus. Cat. No. 52014b. 
 If. Cast of the interior of a ventral valve associated with the specimen represented by figure 1. U. S. Nat. 
 
 Mus. Cat. No. 52018a. 
 Ig. Exterior of a dorsal valve associated with the specimen represented by figure Id. U. S. Nat. Mus. Cat. 
 
 No. .52014c. 
 Ih, li, and Ij. Exteriors of dorsal valves associated with the ventral valve represented by figure la. U. S. 
 
 Nat. Mus. Cat. Nos. 52015d, 52015e, and .5201.5f, respectively. 
 Ik. Interior of a dorsal valve associated with the specimen represented by figiu-e 1. U. S. Nat. Mus. (.'at. 
 
 No. 15436a. 
 1 1. Interior of a dorsal valve, showing visceral area, and muscle scars on the side of the median ridge. Associ- 
 " ated with the specimen represented by figure 1. U. S. Nat. Mus. Cat. No. 52018b. 
 
 Im. Cast of interior of a dorsal valve associated with the specimen represented by figiu-e la. U. S. Nat. 
 
 Mus. Cat. No. 52015g. 
 In. Cast of interior of a dorsal valve associated with the specimen represented by figure 1. U. S. Nat. Mus. 
 
 Cat. No. 15435b. Specimen figured by \\'hite [1877, PL I, fig. 3d] as ^icrotreta ? subsidua. 
 lo. Enlargement of the apex of a ventral valve 7 mm. in length on which the tubercles are small and the 
 
 pedicle aperture large. Locality 30g, Middle Cambrian Marjum limestone in ridge east of ^Mieeler 
 
 Amphitheater, House Range, Utah. U. S. Nat. Mus. Cat. No. 52016a. 
 
 ACROTHELE DICHOTOMA Walcott (p. 644). 
 
 Figure 2. Exfoliated ventral valve from Locality 58, Middle Cambrian Secret Canyon shale in either New York or 
 Secret Canyon, Eureka district, Nevada, showing false area, main vascular sinuses, and apical 
 callosity. U.S. Nat. Mus. Cat. No. 24595a. Type specimen, figured by Walcott [1884b, PL IX, 
 fi.g. 11]. 
 
 ACROTHELE SPURRI Walcott (p. 65fi). 
 
 Figure 3. Top view of the type specimen, which is a partly exfoliated \enlral valve, from Locality 31a, Lower 
 Cambrian limestone near Pioche, Nevada. U. S. Nat. Mus. Cat. No. 15344a. Copied from Walcott 
 [lOOSd, PL VIII, fig. 14]. That figure was redrawn from the specimen illustrated by Walcott [lS8fib, 
 PI. IX, fig. 4] as Acrothele subsidua. 
 
 3a and 3b. Back and side views of a partly exfoliated ventral valve a.ssociated with the specimen represented 
 by figure 3. U. S. Nat. .Mus. Cat. No. 1.5344b. Copied from Walcott [l!l08d, PL VIII, figs. 14" 
 and 14']. 
 
 3c. Exterior of an exfoliated dorsal valve associated with the specimen represented by figure 3. U. S. Nat. 
 -Mus. Cat. No. 15344c. 
 200 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LX 
 
 r 
 
 #: 
 
 3' 
 
 r 
 
 r 
 
 k 
 
 9 
 
 \ 
 
 PRANCES VUIESER DEL. 
 
 MCLlOTYPC CO BOSTOW 
 
PLATE LX. 201 
 
 ACROTHELE GAMAGEI (Hobbs) (p. (>45). 
 
 Figures 5 and 5'. Top view and side outline of a ventral valve. U. S. Nat. iMiis. Cat. .\o. 51986a. 
 5a. Cast of the interior of a ventral valve. U. S. Nat. Mus. Cat. No. 51986b. 
 5b and 5b'. Partly exfoliated specimen of a dorsal valve and side outline of same. Original in the Museum 
 
 of Comparative Zoology; cast in the United States National Mu.seum (Cat. No. 51987a). 
 oc. Cast of the interior of a dorsal valve. U. S. Nat. Mus. Cat. Xo. 51986c. 
 
 The specimens represented are all from Locality 5, Middle Cambrian siliceous .shale on ilayward Creek, Braintree, 
 Massachusetts. * 
 
 AcROTHELE WOODWORTHI Walcott (|). Gfil ). 
 
 Figure U. Top, back, and side views of a cast made from the outer siu-face of a natural mold from Localitv 326c, 
 Lower Cambrian limestone at Nahant, Essex County, Massachusetts. Type specimen in the col- 
 lection of the Boston Society of Natiu-al History; cast in the United States National Museum (Cat. 
 No. 52030a). Copied from Walcott [1908d, PI. IX, fig. ll]. 
 
 AcROTHELE TURNERI Walcott. (p. 660). 
 
 Figures 7 and 7'. Top and side views of a partly crushed veutral valvi-, the type specimen, from Locality 7r, Middle 
 Cambrian shales 4 miles south-southeast of Emigi-ant Peak, Esmeralda County, Nevada. U. S. Nat. 
 Mus. Cat. No. .52028a. Copied fi-om Walcott [1908d, PI. IX, figs. 12 and 12']." 
 7a. Exterior of a compres.sed dorsal valve associated with the specimen represented by figure 7. U. S. Nat. 
 Mus. Cat. No. 52028b. 
 
 AcROTHELE .SUBSIDUA OVllite) (p. 6.o6). 
 
 [PI. LX, flgs. ], la-o.l 
 
 Figure 8. Large compressed ^■entral valve from Locality 14s, Middle ("ambrian Ogi/gopsis zone on Mount Stephen, 
 British Columbia. U. S. Nat. Mus. Cat. No. 24063a. 
 
 AcROTHELE SUBSIDUA HERA Walcott (p. 6.5i)). 
 
 Figures 9 and 9'. Top and side views of an exfoliated ventral valve, the type .specimen, showing the concentric 
 striiB and radiating ridges on the inner layers of the shell. From Locality 31a, Lower Cambrian 
 limestone near Pioche, Nevada. U. S. Nat. Mus. Cat. No. 52024a. Copied from Walcott [1908d, PL 
 VIII, figs. 15 and 15']. 
 
PLATE LXI. 
 
 203 
 
PLATE LXI. 
 
 cl. Cardinal scars. s. Median sopttim. 
 
 F'. Oast of foraminal tube. vs. Vascular sinuses, 
 
 ta. False area. 
 
 ACROTHELE MATTIIEWI (Ilartt) (p. (547). 
 
 Figure 1. Ventral valve fi'om Locality 301j, Middle Cainbriau, St. John formation at Ratcliffs Millstream, St. John 
 County, New Brunswick. Specimen fip:ured tiy Walcolt [1884a, PI. I, ficr. 4a], who stales that it 
 was labeled by Hartt as No. 342, Obolus {Disciiin) nitulus, nov. sp. 
 
 la. Dorsal valve from Locality 301k, Middle Cambrian, St. John formation at St. John, New Brunswick. 
 Type specimen, figured by Hartt [18G8, fig. 221, p. 644], and by Walcott [1884a, PI. T, fig. 4]. 
 
 lb. Top and side views of an interior cast of a ventral valve from I^ocality 3, Vpper Cambrian limestones on 
 Manuels Brook, Conception Bay, Newfoundland. L'. S. Nat. Mus. Cat. No. .51004a. 
 
 Ic. Cast of the interior of a compressed ventral \alve associated with the shell represented by figure lb, show- 
 ing vascular canals. U. S. Nat. Mus. Cat. No. 51004b. 
 
 1<1. Interior of a ventral valve from Locality 6n, Mid<lle Camlirian shales on Manuels Brook, Conception Bay, 
 Newfoundland. U. S. Nat. Mus. Cat. No. 5109Ga. 
 
 le. Exterior of a ventral valve from Locality 6g, Middle Cambrian limestone at Chappie Arm Harbor, Trinity 
 Bay, Newfoundland. U. S. Nat. Mus. Cat. No. 51995a. 
 
 If. Interior of a dorsal valve associated with the shell represented by figtire Id. T'. R. Nat. Miis. Cat. No. 
 51906b. 
 
 Ig. Interior of a dorsal valve from Locality 301j, Middle Cambrian shales on Ratcliffs Millstream, St. John 
 County, New Bruns-iWck. U. S. Nat. Mus. Cat. No. 18170a. 
 
 AcROTHELE MATTHEW! ERYX Walcott (p. 049). 
 
 FiouRE 2. Top and side views of a partly exfoliated \entral valve, the type specimen, from Locality C4, Middle 
 Cambrian limestone, Kiulung group, 3 miles southwest of Yenchuaiig, Sinlai district, .Shantung, 
 China. U. S. Nat. Mus. Cat. No. 52520a. 
 
 ACROTHELE MATTHEWI LATA MattlieW (]). 049). 
 
 Figure 3. Interior of a crushed dorsal valve from Locality 301a, Middle Cambrian sandstones of Division lb3 on Han- 
 ford Brook, St. John County, New Brunswick. University of Toronto, Canada. Type specimen, 
 figured by Matthew [1886, PI. V, figs. 17 and 17a] and by Hall and Clarke [1892c, PI. Ill, figs. 26-28]. 
 
 AcROTHELE PRIMA CO.STATA (^[a(thow) C]). 0.5.'^). 
 
 Figure 4. Top view of a broken ventral valve with numerous co.stie, from Locality 21i, Middle Cambrian sandstones 
 
 of Division lb2 on Hanford Brook, St. John County, New Brunswick. L". S. Nat. Mus. Cat. No. 
 
 .5201 Oa. 
 4a. A crushed ventral valve with three costa"", associated with the shell rciirescnlcd by figvire 4. 1'. S.Nat. 
 
 Mus. Cat. No. 52010b. 
 4b. Interior of a broken dorsal valve associated with tli<' shell represented liy figure 4. 1'. S. Nat. Mus. Cat. 
 
 No. .52010c. 
 4c. Interior of a dorsal valve from Locality 6n. Middle Cambrian shales on Manuels Brook, Conception Bay, 
 
 Newfoundland. U. S. Nat. Mus. Cat. No. 51084a. 
 4d. Enlargement of the outer surface of a specimen associated with ihe shell rc])resented by figure 4. U. S. 
 
 Nat. Mus. Cat. No. 52010d. 
 204 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LXI 
 
 /■ ( 
 
 
 f-i^-- 
 
 '- 1 
 
 
 FRANCES WIE9ER DEL. 
 
 HCLiOTypc CO eo5To« 
 
PLATE LXI. 205 
 
 ACROTHELE MATTHEWI MULTICOSTATA MattheW (p. 650). 
 
 Figure 5. Top and side views of a voiilral valve ]ii-eserving the outer surface from Locality 21, -Middle Cambrian shale 
 at the base of the Paradoxides zone on llanford Brook, St. John County, Xew Brunswick. V. S. Nat. 
 Mus. Cat. No. 56633a. 
 5a. Partly exfoliated ventral valve, with apex broken off. Locality 2t, Middle t'ambrian shales at Hastings 
 
 Cove on Kennebecasis Bay, St. John County, New Brunswick. U. S. Nat. Mus. Cat. No. .52000a. 
 5b. Fragment showing the numerous cost*. University of Toronto, Canada. (Locality unknown.) 
 5c. Exfoliated dorsal valve associated with the specimen represented by figure 5a. U. S. Nat. Mus. Cat. No. 
 52000b. 
 
 AcROTiiELE PRIMA (Matthew) (p. ().53). 
 
 [I'l. LXII, flg. 2.] 
 
 Figure 6. Top view of a small ventral \-alve from Locality 2g, Middle Cambrian sandstones of Division Ibl of 
 Matthew's ProtoUnus zone, Hanford Brook, St. John County, New Brunswick. University of 
 Toronto, Canada. Type specimen, figured by Matthew [1886, PI. V, figs. 16 and 16a] as Acrothele 
 maUhevi prima. The specimen has been figured and refigured; see page 653 for record. 
 
 6a. Natural cast of the exterior of a ventral valve from Locality 2i, Middle Cambrian limestone of Division 
 lbs on Hanford Brook, .St. John County, New Brunswick. U. S. Nat. Mus. Cat. No. .56638a. 
 
 6b. A ventral valve with a cast of the exterior of a dorsal valve beside it. Associated with the specimen repre- 
 sented by figure 6a. V. S. Nat. Mus. Cat. No. ■56638b. 
 
 Acrothele avia Matthew (p. 634). 
 
 [PI. LXII, fiys. 1, la-k.] 
 
 Figure 7. Exterior of a ventral \al\e from Locality 344b, Middle Cambrian shales of Division E3d of Matthew's 
 Etcheminian, Dugald Brook, Cape Breton, Nova Scotia, University of Toronto, Canada. Speci- 
 men figured by ilatthew [1902b, PI. XVII, fig, 2a]. 
 
 7a, Interior of a broken ventral valve from Locality 13n', Middle Cambrian shales of Division E3e of Matthew's 
 Etcheminian, Dugald Brook, Cape Breton, Nova Scotia, Univer-iity of Toronto, Canada. Type 
 specimen, figured by Matthew [1899b, PI, III, fig. Ic], 
 
 7b. Interior of a dorsal valve from the locality represented by figure 7a. University of Toronto, Canada. 
 Specimen figured by Matthew [1899b, PI. Ill, fig. If]. 
 
PLATE LXII. 
 
 207 
 
PLATE LXII. 
 
 c. Area. j. Anterior lateral muscle scar, 
 
 cl. Cardinal scar. k. Middle lateral muscle scar. 
 F'. Cast of foraminal tube. 1. Outside lateral muscle scar, 
 
 h. Central muscle scar. vs. Vascular sinus. 
 
 AcROTHELE AVI A ]\Iatthew (p. 6.34). 
 
 [Pi. LXI. figs. r. 7a-l).l 
 
 Figure 1. Top view of a typioal lonii of ilio ventral valve from Locality 13n', Middle Cambrian sand.stones of Dhdsion 
 E3e of Matthew's section, Diigald Brook. Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. No. .56.598a. 
 
 la. To]) view of a ventral valve nearly circular in outline from Locality 13d", Mid<lle Cambrian sandstone.? 10 
 feet l)elow top of Divi.sion E2a of Matthew's section, Dugald Brook, Cape Breton, Xova Scotia. L". S. 
 Xat. Mus. Cat. .\o. SGGOla. 
 
 lb. Laterally compressed ventral valve from Locality 131', Middle Cambrian sandstones of Division E3a on 
 Dugald Brook. Cape Breton, Nova Scotia. V. S. Xat. Mus. Cat. No. 51970a. 
 
 Ic. Partly exfoliated ventral valve from Locality 13m, Middle Cambrian sandstones of Division E3f on 
 Gillis Brook, Cape Breton. Xova .'^cotia. T'. S. Xat. Mtis. Cat. X'o. 56596a. The surface of this 
 specimen is enlarged in figure Ij. 
 
 Id. E.xf(jliated ventral valve (locality unknown). L'niversity of Toronto. Canada. 
 
 le. Fragment of the interior of a ventral valve associated with the specimen represented by figure 1 L". S. 
 Xat. Mus. Cat. Xo. 56598b. 
 
 If. Cast of interior of dorsal valve, from Locality 13n, Middle I'amlMian sandstones of Division E3f of Mat- 
 thew's section, Dugald Brook, Cape Breton, Xova Scotia. L'. S. Xat. Mus. Cat. Xo. 56597a. 
 
 Ig. Interior of dorsal valve associated with the specimen represented by figure Ic. I'. S. Xat. Mus. Cat. Xo. 
 565961). 
 
 Ih. Interior of a compres.sed dorsal valve placed with tlie specimens from Locality 13m; tlie exact locality is, 
 however, unknown. V. S. Xat. Mus. Cat. Xo. 56596c. 
 
 li. Exfoliated dorsal valve from Locality 344b, Middle Cambrian shales of Division E3d of Matthew's 
 Etcheminian, Dugald Brook, Cape Breton, Xova Scotia. University of Toronto. Canada. Specimen 
 figured by Matthew [1902b, PI. XVII. fig. 21)]. 
 
 Ij. Enlargement of a portion of the surface of the specimen represented Ijy figure Ic. 
 
 Ik. Posterior portion of a ventral valve showing the apex. Associated with the specimen represented by- 
 figure lb. U. S. Xat. Mus. Cat. Xo. 51970b. 
 
 AcROTHELE PRIMA (MattllOW) (]). 6.l3). 
 [PI. LXI.flgs. i',.(ja-b.] 
 
 Figure 2. Partly exfoliated ventral valve from Locality 13t, Middle Camlirian shaly sandstones of Division Elb on 
 Dugald Brook, Cape Breton, Xova Scotia. U. S. Xat. Mus. Cat. Xo. 5200')a. 
 
 AcROTHELE PROLES Matthew (p. 654). 
 
 Figure 3. Exterior of a slightly compressed ventral valve from Locality 13m, Middle Cambrian shaly sandstones f>f 
 
 Division E3f on Gillis Brook, Cape Breton, Xova Scotia. V. S. Xat. Mus. Cat. Xo. 52011a. 
 3a. Portion of a dorsal valve associated with the specimen represented by figure 3. V. S. Xat. Mus. Cat. 
 
 Xo. 52011b. 
 31). Interior of a fragmentary ventral valve associateil with the specimen repre.sented by figiu'e 3. I". S. Xat. 
 
 Mus. Cat. Xo. 520lic. 
 3c. Interior of a small slightly distorted veiilial valve a.^sociated with the specimen represented by figure 3. 
 
 U. S. Xat. Mus. Cat.Xo. 5201 Id. 
 3d. Partly exfoliated dorsal valve as.sociated with the specimen iciirescntcil by figure 3. I". S. Xat. Mus. Cat. 
 
 Xo. 5201 le. 
 3e. Partly exfoliated dorsal valve, showing va.scular markings on the inner layers of the shell. Locality 
 
 13n. Middle Cambrian .shaly sandstones of Di\Tsion E3f on Dugald Brook, Cape Breton, Xova Scotia. 
 
 U. S. Xat. Mus. Cat. Xo. 52012a. 
 208 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LXII 
 
 
 •FRANCES WIE3EB DEL. 
 
 HELIOTYPE CO.. 80ST0N. 
 
PLATE LXII. 209 
 
 AcROTHELE PROLES Matthew — Continued. 
 
 Figure 4. A cast of the cxlerior of tlio ventral valve, preserving a portion of the shell. From Locality 13m, 
 Middle Cambrian sandstone of Division E3f of Matthew's Etcheminian, Oillis lirook, Cape Breton, 
 Nova Scotia. University of Toronto, Canada. Type specimen, figured bv Matthew [1902b, PI. 
 XVII, fig. 3a]. 
 4a. Fragment of the interior of a dorsal valve (locality unknown). Universit)' of Toronto, Canada. The 
 specimen from which this figure is drawn can not be identified with any of the figures given bv Mat- 
 thew [1902b, PI. XVII, fig.s. 3a-e]. 
 
 BoTSFORDiA PULCHRA Matthew (p. 607). 
 
 Figure 5. Exterior and side view of ventral valve. (See note following fig. 5 1.) 
 
 5a. Exterior of ventral valve, with reticulate surface ornamentation on young .sliell only. U. S. Nat. Mus, 
 
 Cat. No. 52047a. 
 5b. Exterior of ventral valve. U. S. Nat. Mus. Cat. No. 52047b. 
 5c. Exterior and side view of dorsal valve. (See note following fig. 5 1.) 
 5d. Exterior of dorsal valve. U. S. Nat. Mus. Cat. No. 52047c. 
 5e. Exterior of ventral valve. U. S. Nat. Mus. Cat. No. 52047d. 
 5f and 5f'. Top and back views of a ventral valve. U. S. Nat. Mus. Cat. No. 52047e. 
 5g. Cast of the interior of a ventral valve. U. S. Nat. Mus. Cat. No. 52047f. 
 
 5h and 5j. Casts of the interior of dorsal valves. U. S. Nat. Mus. Cat. Nos. 52047g and 52047h, respectively. 
 5k. Portion of surface, greatly enlarged, of the specimen represented by figure 51. U. S. Nat. Mus. Cat. 
 
 No. 52047i. 
 51. Exterior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52047i. 
 
 The specimens represented are all from Locality 2y, Middle Camlirian sandstone on Catons Island, Long Reach, 
 St. John River, New Brunswick, with the possible exception of the specimens represented by figures 5 and 5c, which 
 can not now be located in the collections of the United States National Museum. These figures may have been 
 drawn from specimens loaned to the Museum and since returned. 
 62667°— VOL 51, pt 2—12 14 
 
PLATE LXIII. 
 
 211 
 
PLATE LXIII. 
 
 cl. Cardinal scars. 
 
 f. Flexure line of area. 
 F'. Cast of foramina! tube, 
 h. Central muscle scar. 
 
 i. Transmedian muscle scar. 
 
 j. Anterior lateral muscle scar, 
 k. Middle lateral muscle scar. 
 1. Outside lateral muscle scar, 
 p. I'edicle furrow. 
 s. Median septum. 
 
 AcBOTHELE CERATOPYGARr.M (Broggcr) (p. 640). 
 
 Figures 1 and la. Top and side views of a ventral valve, the type .specimen, from Locality 323h, pa.ssagc beds 
 between the Upper Cambrian and the Or(lo\-ician, Ceratopyge limestone at Vestfossen, 10 miles south- 
 southwest of Christiania, Norway. Copied from Brogger's figures [1882, PI. X, figs, la and ]b] of 
 Discina (Acrotrcta ?) ceratopyyaram. 
 lb and Ic. Top and side \dews of an exfoliated ventral \ah"e as.sociated with the valve represented by figures 
 1 and la. V. S. Nat. Mus. Cat. No. 51977a. 
 
 ACROTHELE BORGHOLMEXSIS Walcott (p. 639). 
 
 Figures 2 and 2a. Top and side views of a partly exfoliated \entral valve, the type specimen, from Locality 310d, 
 Upper Cambrian Ceratopyge slate at Borgholm, Oeland Island, Sweden. V . S. Xat. Mus. Cat. No. 
 51974a. Copied from Walcott [1908d, PI. VIII, figs. 12 and 12']. 
 2b. Interior of a small dor.^al valve associated with the specimen represented by figun s 2 and 2a. I'. S. Xat. 
 Mus. Cat. No. 51974b. 
 
 ACROTIIELE? MINUTA Walcott (p. 650). 
 
 FiGUiiE 3. Exterior view of a partly exfoliated dorsal valve, the type specimen, from Localily C6, Middle Cambrian 
 shaly limestone 2.5 miles southwest of Yenchuang, J-^intai district , Shantung, China. U. S. Nat. Mus. 
 Cat. No. 52519a. 
 
 AcROTHELE RARA Willcott (p. 6.55). 
 
 Figure 4. Cast of interior of a ventral valve, the type specimen, from Locality C57, Middle Cambrian shale 3 miles 
 south of Kaokiapu, Sintai district. Shantung, China. U. S. Nat. Mus. Cat. No. 52518a. 
 4a. Cast of interior of a dorsal valve associated with the shell represented by figure 4. I'. S. Nat. Mus. Cat. 
 No. 52518b. 
 
 AcROTHELE sp. lindt. <t "Willcott (p. 662). 
 
 Figure 5. Top and side view of type specimen from Locality 319b. Lower Cambrian limestone at St. Simon, 
 Quebec, Canada. V . S. Nat. Mus. Cat. No. 52032a. 
 
 ACROTIIELE COLLENI Walcott (p. 640). 
 IText figs. oo.V-E, p. 041.] 
 
 Figures (i ami 6'. Top and side views of the type .specimen, a veiKral vahr, from Localily 4q, Middle Cambrian 
 .shale near Gordon Mountain, Ovando quadrangle, Montana. V . S. Nat. Mus. Cat. No. 51973a. 
 6a and Ga'. Top and back views of the posterior portion of a ventral valve associated with the shell rejjre- 
 
 sented by figure 6. U. S. Nat. Mus. Cat. No. 51973b. 
 6b. Exterior of dorsal valve associated with the shell represented by figure 6. L. S. Xat. Mus. Cat. Xu. 
 51973c. 
 212 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LXIII 
 
 (%: 
 
 /'^^ 
 
 2' 
 
 4= 
 
 8^ 
 
 ^^Hrf 
 
 
 1 
 
 ; h 
 ! k 
 
 / 
 
 ^1 
 
 
 
 
 I0» 
 
 
 FRANCES WIESER DEL 
 
 
 
 10" 
 
 HCLIOTYPC CO BQS-ON 
 
PLATE LXIII. 213 
 
 Helmersenia ladogensis (Jeremejow) (p. .368). 
 
 Figure 7. Extorior view and side outline of a ventral valve from Locality 336p, li|i]icr Camlirian sandstone at Kunitz, 
 
 Pskow, Russia. U. S. Nat. Mus. Cat. No. 51941a. 
 7a. Exterior of a transverse dorsal valve from Locality 336o, Upper Cambrian sandstone at Koporje, St. Peters- 
 burg, Russia. U. S. Nat. Mus. Cat. No, 51940a. 
 7b and 7b'. Exterior of a rounded ventral valve, and side outline, a.ssociated willi the specimen represented 
 
 by figure 7a. U. S. Nat. Mus. Cat. No. 51940b. 
 7c. Posterior view of a donsal valve from Locality 336q, Upper Cambrian .sandstone near Ladoga, Government 
 
 of St. Petersburg, Ru.«.sia. Copied from Pander [1861, PI. II, fig. 2f] 
 7d. Interior view of a ventral valve, the type specimen, associated with (he valve represented by figure 7c. 
 
 Copied from Pander [1861, PI. II, fig. 2d]. 
 7e. Exterior of a dorsal ? valve associated with the specimen represented liy figure 7a. IT. S. Nat. Mus. Cat. 
 
 No. 51940c. 
 7f. Interior of a ventral? valve a.ssociated ■sWth the specimen represented by figure 7a. U. S. Nat. Mus. Cat. 
 
 No. 51940d. 
 
 Oboiat.s (Westonia) elongatus Wiilcott (p. 4.59). 
 
 Figure 8. Compressed, exfoliated ventral valve. U. S. Nat. Miis. Cat. No. 51722b. 
 
 8a. Exfoliated interior of a ventral valve, the type specimen, li. S. Nat. Mus. Cat. No. 51722a. Copied 
 
 from Walcott [1908d, PI. VII, fig. 12]. 
 8b and 8c. Exfoliated interiors of dorsal valves. U. S. Nat. Mus. Cat. Nos. 51722c and 51722d, respectively. 
 8d. Enlargement of a portion of the matrix of the outer surface of the dorsal valve represented by figure 8b. 
 
 The spaces inclosed by the obliciue lines are not so convex as represented on the figure. U. S. Nat. 
 
 Mus. Cat. No. 51722c. 
 
 The specimens represented are all from Locality 105x, Middle Orduviciaii shales in Wasatch Canyon, north of 
 Brigham, Boxelder County, Utah. 
 
 Obolus (Westonia) notchensis Walcott (p. 46.3). 
 
 Figure 9. Fragment of a ventral valve, the type specimen, preserving a portion of the outer surface, from Locality 
 lost. Lower Ordovician limestone on Notch Peak, House Range, Utah. XJ. S. Nat. Mus. Cat. 
 No. 51731a. Copied fr..m Walcott [1908d, PI. VII, fig. 13]. 
 
 Obolus (Fordinia) perfectxis Walcott (p. 429). 
 
 Figures 10 and 10'. Exterior and side \'iew of a ventral valve. U. S. Nat. Mus. Cat. No. 51947b. 
 
 10a. Interior of a ventral valve, the type specimen. U. S. Nat. Mus. Cat. No. 51947a. Copied from 
 
 Walcott [1908d, PI. VII, fig. 16]. 
 10b. Exterior and side Aaew of a dorsal valve. U. S. Nat. Mus. Cat. No. 51947c. 
 10c and lOd. Interiors of dorsal valves. V. S. Nat. Mus. Cat. Nos. 51947d and 51947e, respectively. 
 
 The specimens represented are all from Locality 30n, Middle Cambrian Weeks limestone, in Weeks Canyon, 
 House Range, Utah. 
 
1 
 
PLATE LXIV. 
 
 215 
 
PLATE LXIV. 
 
 a. Outer lateral space of area. 
 cl. Cardinal scars. 
 
 f. Fle.xure line of area, 
 fa. False area, 
 p. False pedicle groove. 
 
 h. Central scars. 
 
 s. Median septum or ridge. 
 
 V. Visceral area. 
 vs. Main vascular sinus. 
 .x". Cast of apical callosity. 
 
 ACROTRETA ATTENUATA Meek (p. 675). 
 [PI. LXXIX, figs. 6 and 6a.J 
 
 Figures 1, 1', 1", and la, la', la". Top views with side and back views of ventral valves in the material upon which 
 
 Meek founded the species. From Locality 302, Middle Cambrian limestone east of West Gallatin 
 
 (Gallatin) River, above Gallatin, Montana. U. S. Nat. Mus. Cat. Nos. 7867a and 7867b, respectively. 
 
 Figure 1 represents the type specimen, 
 lb, lb', lb", and Ic, Ic', Ic". Top, side, and back views of two ventral valves from Locality 166a, Middle 
 
 Cambrian limestones north of East Gallatin River, near Hillsdale, Montana. U. S. Nat. Mus. Cat. 
 
 Nos. 52063a and 52063b, respectively. 
 Id, Id', Id"; le, le', le"; and If, If, If". Top, side, and back views of three ventral valves, from Locality 4n, 
 
 Middle Cambrian lunestone in the divide at the head of Jackson Creek, Teton Mountains, Wyoming. 
 
 U. S. Nat. Mus. Cat. Nos. 52067a, 52067b, and 52067c, respectively. 
 Ig, Ig', and Ig". Top, side, and back views of a ventral valve from Locality 159, Middle Cambrian limestone 
 
 on the north side of West Gallatin (Gallatin) River, Montana. U. S. Nat. Mus. Cat. No. 52064a. 
 Ih. Dorsal valve associated with the ventral valves represented by figiu'es 1 and la. U. S. Nat. Mus. Cat. 
 
 No. 7867c. 
 li. Interior of ventral valve, showing base uf apical callosity, vascular sinuses, and cardinal scars. From 
 
 Locality lOy, Middle Cambrian Marjum limestone, southeast of Maxjum Pass, House Range, Utah. 
 
 U. S. Nat. Mus. Cat. No. 52070a. 
 Ij, Ik, and 1 1. Top, back, and side views of a cast of the interior of a ventral valve associated with the shell 
 
 represented by figure li. U. S. Nat. Mus. Cat. No. 52070b. 
 Im. Interior of a dorsal valve associated with the specimen represented by figiu-e li. U. S. Nat. Mus. Cat. 
 
 No. 52070c. 
 In. Interior of a dorsal valve from Locality 3s, Middle Cambrian shales of the Wheeler formation, east of Ante- 
 lope Springs, House Range, Utah. U. S. Nat. Mus. Cat. No. 52069a. 
 lo. Exterior of a dorsal valve associated with the specimen represented by figtire In. U. S. Nat. Mus. Cat. 
 
 No. 52069b. 
 
 AcROTRETA DEFINITA Walcott (p. 683). 
 
 Figures 2, 2', 2"; 2a, 2a', 2a"; and 2b, 2b', 2b". Top, side, and back views of tj-pical forms of the ventral valve. 
 
 U. S. Nat. Mus. Cat. Nos. 35270a, 35270b, and 35270c, respectively. 
 2c, 2c', and 2c". Cast of the interior of a ventral valve, the type specimen, with back and side views. 
 
 U. S. Nat. Mus. Cat. No. 35270d. 
 2d, 2d', and 2d". Top, back, and side views of the cast of the interior of a dorsal valve, showing the area, 
 
 cardinal scar, etc., with unusual clearness. U. S. Nat. Mus. Cat. No. 35270e. 
 2e, 2f, and 2g. Exterior views of three dorsal valves, illustrating variation in outline. U. S. Nat. Mus. Cat. 
 
 Nos. 35270f, 35270g, and 35270h, respectively. 
 
 The specimens represented by figures 2, 2a-g are from Locality 163, Middle Cambrian Spence shale member of 
 Ute limestone, Spence Gulch, 15 miles west of Montpelier, Idaho. 
 
 Figures 3, 3a, and 3b. Top, back, and side views of a cast of a ventral valve from Locality 55, Middle Cambrian 
 Eldorado limestone in New York Canyon, Eureka district, Nevada. U. S. Nat. Mus. Cat. No. 
 35271a. 
 216 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LXIV 
 
 '\ ^ ^ x 
 
 3 
 
 ^ 
 
 3 
 
 / 
 
 1%. 
 
 ^nS. 
 
 z4W 
 
 I' 
 
 >« 
 
 ^ir^ 
 
 J . 
 
 
 _..j 
 
 2» 
 
 2 
 
 H 
 
 > 
 
 .1 I : 
 
 ,/i 
 
 ^ , 3 
 
 2^- 
 
 2? 
 
 FRANCES WIESEft OEL. 
 
 MELIOrvPE CO ROSTOH 
 
PLATE LXV. 
 
 217 
 
PLATE LXV. 
 
 a. Area. 
 
 a'. Outer lateral space of area, 
 ol. Cardinal scars, 
 fa. False area, 
 fp. False pedicle groove. 
 
 h. Central scars. 
 
 s. Median septum or ridge. 
 vs. Main vascular sinus. 
 x". Cast of apical callosity. 
 
 ACROTRETA IDAHOENSIS Walcott (j). 687). 
 [Fl. LXVIII, figs. 2, 2a-g.l 
 
 Figures 1, V, 1"; la, la', la"; lb, IV, lb"; and Ic, Ic', Ic". Top. side, and back views of tj'pical forms of the ventral 
 valve. U. S. Nat. Mus. Cat. Nos. 52091a, 52091b, 52091c, and 52091d, respectively. Figure lb repre- 
 sents the type specimen. 
 
 Id, Id', and Id". Top, back, and side views of cast of the interior of a ventral valve. V. S. Nat. Mus. Cat. 
 No. 52091e. 
 
 le. Cast of the interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52091f. 
 
 If. Interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52091g. 
 
 Ig. Natural cast of tlie interior of the dorsal valve represented by figure If. U. S. Nat. Mus. Cat. No. 52091g. 
 
 Ill and li. Exteriors of two dorsal valves. U. S. Nat. Mus. Cat. Nos. 52091h and 520911, respectively. 
 
 The specimens represented are all from Locality 5c, Upper Cambrian limestone in Twomile Canyon, 2 miles south- 
 east of Malade, Idaho. 
 
 AcROTRETA ATTENUATA var. Walcott (p. 676). 
 
 Figures 2, 2', and 2". Top, side, and back views of a specimen with a more distinctly marked false area than usually 
 occurs in typical A. attenuata. Associated with the type of that species in Locality 302, Middle ( 'aui- 
 brian limestone east of West Gallatin (Gallatin) River above Gallatin, Montana. V. S. Nat. Mus. 
 Cat. No. 52071a. 
 
 AcROTRETA KUTORGAI Walcott (p. 692). 
 [Te.\t fig. 58, p. 693.] 
 
 Figures 3, 3', 3", and 3a, 3a', 3a". Top, back, and side \'iews of the exterior of two ventral valves from Locality 139a, 
 
 Middle Cambrian limestone near Chepultepec, Jefferson County, Alabama. U. S. Nat. Mus. Cat. 
 
 Nos. 58305a and 58305b. 
 3b, 31)'. 3b", and 3c, 3c', 3c". Top, back, and side views of casts of the interior of Aentral valves. U. S. Nat. 
 
 Mus. Cat. Nos. 35277a and 35277b, respectively. Figure 3b represents the type specimen. 
 3d. Side \'iew of cast of ventral valve, showing cast of pedicle tube. V. S. Nat. Mus. Cat. No. 35277c. 
 3e. Cast of pedicle tube, showing lines of shell growth. U. S. Nat. Mus. Cat. No. 35277d. 
 3g. View into cast of ventral valve, with cast of area of dorsal valve in position. U. S. Nat. Mus. Cat. No. 
 
 35277e. This specimen is tipped so as to show the cast of the areas of both the ventral and dorsal 
 
 valves in text figure 58, page 692. 
 3h, 31, 3j, and 3k. Casts of interiors of dorsal valves, illustrating variation in median ridge, muscle scars, etc. 
 
 U. S. Nat. Mus. Cat. Nos. 35277f, 35277g, 35277h, and 352771, respectively. 
 
 The specimens represented by figtires 31>-k are all from Locality 90x, Middle Cambrian siliceous nodules in the 
 Conasauga shale, Coosa Valley, Cherokee County. Alaliania. 
 
 AcROTRETA RUDis Walcott (j). 702). 
 
 (I'l. LXXV, fig. 1.) 
 
 Figure 3f. Ventral valve, the tj^jc specimen, flattened in the shale of Locality 101a, Middle Cambrian. 3.5 miles south- 
 west of KoKcrsville. Hawkins County, Teimessee. U. S. Nat. Mus. Cat. Xo. 52111a. Copied from 
 \\ulcott [1908d, PI. IX, fig. 5]. 
 218 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LXV 
 
 
 I'' 
 
 I ID 
 
 
 J 
 
 ^/^m 
 
 i 
 
 fa |c- 
 
 * 
 
 fp 3' 
 
 ^ 
 
 .^^^i^ 
 
 ^1 
 
 n\^' "^ 
 
 IM 
 
 IV .^ 
 
 4" 
 
 FRANCES WIESER DEL 
 
 LioTvpe CO BOSTON 
 
PLATE LXV. 219 
 
 ACROTRETA IDAHOENSIS ALTA Walcott (p. 689). 
 
 Figures 4, 4', and 4". Top, side, and Ijack views of a ventral valve from Locality 15d, Upper Cambrian limestone near 
 Cave Spring, Fish Spring Range, Utah. U. S. Nat. Mus. Cat. No. 52099a. 
 
 4a, 4a', and 4a". Top, side, and Ixick views of a ventral valve from Locality 88, Middle Cambrian shaly lime- 
 stone in either New York or Secret Canyon, Eureka district, Nevada. U. S. Nat. Mus. Cat. No. 
 35273a. Type specimen, figured by Walcott [1884b, PI. I, fig. la], 
 
 4b. Dorsal valve associated with the specimen represented by figure 4. U. S. Nat. Mus. Cat. No. 52099b. 
 
 ACROTRETA IDAHOENSIS SULCATA Walcott (p. 690). 
 
 Figures 5, 5', and 5". Top, side, and back views of a ventral valve, the type specimen, with the apex broken off. 
 From Locality 322a, Middle Cambrian Langston limestone near Paris, Idaho. U. S. Nat. Ma'?. Cat. 
 No. 35275a. 
 
 AcROTRETA EMMONSI Walcott (p. 684). 
 
 Figure 6. Cast of the interior of a dorsal valve, the type specimen, from Locality 35a, Lower Cambrian limestone on 
 Bald Mountain, Washington County, New York, showing vascular markings and muscle scars. 
 U. S. Nat. Mus. Cat. No. 52087a. 
 
PLATE LXVI. 
 
 221 
 
PLATE LXVI. 
 
 a'. Outer lateral spaoe of area. s. Median septum or ridge, 
 
 cl. Cardinal scar. vs. Main vascular sinus, 
 
 fp. False pedicle groove. x". Cast of apical callosity, 
 h. Central muscle scar. 
 
 AcROTRETA GEMMA Billings (p. 6S5). 
 
 Figures 1, 1', 1", and la, la', la". Top, side, and back views of two ventral valves from Locality 314d, Lower Ordovi- 
 cian limestone 4 miles northeast of Portland Creek, Newfoundland. Mus. Geol. Survey Canada. 
 Figure 1 may be taken as the type, 
 lb. Enlargement of the apex anil foraminal opening of a ventral valve associated with (he specimeDS repre- 
 sented by figures 1 and la. 
 
 Figures 1, la-b are drawn from the specimens illustrated Ijy Billings [1865, figs. 201b, d, c, and f]. 
 
 AcROTRETA ovALis Walcott (p. 699). 
 
 Figures 2, 2a, and 2b. Top, side, and back views of the type specimen, a ventral valve, from Locality 314d, Lower 
 Ordovician limestone 4 miles northeast of Portland Creek, Newfoundland. Mus. Geol. Survey Canada. 
 
 AcROTRETA GEMMULA MatthcW (p. 686). 
 
 [PI. LXXVII, figs. 5,5a-f.l 
 
 Figures 3, 3', and 3". Top, back, and side views of the outer surface of a ventral valve (locality unknown). Univer- 
 sity of Toronto, Canada. 
 
 3a. Top, back, and side \dews of the cast of the interior of a ventral valve in which the ca.«t of the ba.se of the 
 foraminal tube is unusually large. Locality 301a, Middle Cambrian sandstones in Divi.sion IbS of 
 Matthew on Hanford Brook, St. John County, New Brunswick. University of Toronto, Canada. 
 Type specimen, figured by Matthew [1894, PI. XVI, fig. 2a]. 
 
 3b and 3c. Cast and interior of a dorsal valve from the locality represented by figure 3a. University of 
 Toronto, Canada. Specimen figured by Matthew [1894, PI. XVI, fig. 2b]. 
 
 AcROTRETA SAGITTALIS MAGNA (Matthew) (p. 706). 
 
 Figures 4 and 4a. Top and side vaews of a cast of the interior of a ventral valve from Locality 2s, Middle Cambrian 
 
 limestone at Hastings Cove, northeast of St. John, New Brunswick. University of Toronto, Canada. 
 
 Specimen figured by Matthew [1897b, PI. I, fig. lb] as Linnarssonia helti magna. 
 4b. Cast of the interior of a dorsal valve from the locality represented by figure 4. I'niversity of Toronto, 
 
 Canada. Type specimen, figiu'ed by Matthew [1897b, PL I, fig. la] as Linnarssonia belli magna. 
 4c, 4c', and 4c". Top, back, and side views of a small well-preserved ventral valve from Locality 2 1, Middle 
 
 Cambrian limestone on Hanford Brook, St. John Coimty, New Brunswick. U. S. Nat. Mus. Cat. 
 
 No. 35284a. 
 4d. Interior of a partly crushed ventral valve associated with the shell represented by figure 4c. U. S. 
 
 Nat. Mus. Cat. No. 35284b. 
 4e and 4f . Interior of a dorsal valve and natural cast of same associated with the shell represented by figure 4c. 
 
 U. S. Nat. Mus. Cat. Nos. 35284c and 35284d, respectively. 
 
 ACROTKETA GRACIA Walcott (p. 687). 
 
 Figures 5, 5', and 5". Top, back, and side views of a ventral valve. U. S. Nat. Mus. Cat. No. 35272a. 
 
 5a, 5a', and 5a". Top, back, and side xnews of a cast of a ventral valve, the type specimen. U. S. Nat. Mus. 
 
 Cat. No. 35272b. 
 5b. Cast of part of the interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 35272o. 
 5c and 5c'. Top, side, and back views of a cast of a dorsal valve. U. S. Nat. Mus. Cat. No. 35272d. 
 5d. Cast of the exterior of a dor.sal valve, with a portion of the posterior part of the shell. U. S. Nat. Mus. 
 Cat. No. 35272e. 
 The specimens represented arc all from Locality 2s, Middle Cambrian limestone at Hastings Cove, on Kennebecasis 
 Bay, northeast of St. John, New Brunswick. 
 222 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LXVI 
 
 pr , ifll J^k %m..s ^^ 
 
 / 
 
 !■' I'' 
 
 ^_ 
 
 r 
 
 ^^ 
 
 3' 
 
 
 la 
 
 4' 
 
 4'' 
 
 5' 
 
 5" 
 
 ^ 6 6" \ _^^r 
 
 6"' 
 
 B'- 
 
 5":' 
 
 '% 
 
 73- 
 
 t; 
 
 74' 
 
 8" 
 
 FRANCES WieSER DEL. 
 
 MELIOTVPE CO aoSTON 
 
PLATE LXVI. 223 
 
 AcROTRETA CON VEX A Walcott (p. 682). 
 
 Figure 6. Cast of the interior of a ventral valve, the type specimen, from Locality 3n, Upper Cambrian sandstones 
 
 on Salmon River, Gillis Hill, Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. No. 35268a. 
 6a. Cast of the interior of a dorsal valve associated with the shell represented by figure 6. U. S. Nat. Mus. Cat. 
 
 No. 35268b. 
 6b, 6b', and 6b". Top, side, and back views of the cast of a ventral valve from Locality lOi, Upper Cambrian 
 
 shale on Barachois River, just north of the Boisdale Road, Cape Breton, Nova Scotia. U. S. Nat. 
 
 Mus. Cat. No. 52084a. 
 6c. Cast of interior of dorsal valve from Locality lOe, Upper Cambrian shales on east branch of Barachois 
 
 River, north of the crossroad from Boisdale to Upper Leitches Creek, Cape Breton, Nova Scotia. 
 
 U. S. Nat. Mus. Cat. No. 52085a. 
 
 AcROTRETA BisECTA Mattliew (p. 678). 
 
 Figures 7, 7', and 1" . Top, side, and back views of a parJy exfoliated ventral valve. V . S. Nat. Mus. Cat. No. 
 ,52073a. 
 7a, 7a', and 7a". Top, side, and back views of cast of ventral valve. U. S. Nat. Mus. Cat. No. 52073b. 
 7b. Interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52073c. 
 7b'. Enlargement of the area of figure 7b. 
 
 7c. Cast of the interior of a dorsal valve on which the lines of growth about the cardinal scars are beau- 
 tifully shown. U. S. Nat. Mus. Cat. No. 52073d. 
 7d. Cast of the interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52073e. 
 
 The specimens represented by figures 7, 7a-d are from Locality 3q, Upper Cambrian shale in Barachois Glen, 
 south of Little Bras d'Or Lake, Cape Breton, Nova Scotia. 
 
 Figure 7e. Cast of the interior of the posterior portion of a ventral valve in which the cast of the main vascular sinuses 
 is finely preserved; also the cast of the base of the pedicle tube. Locality lOe, L'pper Cambrian shales 
 on east branch of Barachois River, north of crossroad from Boisdale to Upper Leitches Creek, Cape 
 Breton, Nova Scotia. U. S. Nat. Mus. Cat. No. 52077a. 
 
 ACROTRETA DEPRESSA (Walcott) (p. 683). 
 
 Figures 8 and 8'. Top, side outline, and back view of the type specimen, a cast of the interior of a compressed ventral 
 
 valve, from Locality 14s, Middle Cambrian shaly limestones {Ogygopsis zone) on Mount Stephen, 
 
 British Columbia. U. S. Nat. Mus. Cat. No. 52086c. Copied from Walcott [1908c, PI, I, fig. 3c]. 
 8a and 8b. Casts of the interior of two dorsal valves associated with the shell represented by figure 8. U. S. 
 
 Nat. Mus. Cat. Nos. 52086a and 52086b, respectivelv. Figure 8a is copied from Walcott [1908c, PL I, 
 
 fig. 3b]. 
 8c, 8c', and 8c". Top, side, and back \-iews of a ventral valve occurring in the same beds with the specimens 
 
 represented by figures 8, 8a-b, but which is very doubtfully referred to this species. U. S. Nat. 
 
 Mus. Cat. No. 52086d. Figures 8c and 8c' are copied from Walcott [1908c, PI. I, figs. 3 and 3a, 
 
 respectively]. 
 
} 
 
PLATE LXVII. 
 
 62667°— VOL 51, pt 2—12 15 
 
PLATE LXVII. 
 
 cl. Cardinal scar. 
 
 fa. False area. 
 
 fp. False pedicle groove. 
 
 h. Central muscle scar. 
 
 1. Outside lateral muscle scar. 
 
 s. Median septum. 
 
 V. Visceral cavitj-. 
 X. Foraminal aperture, 
 x'. Ca.st of foraminal aperture. 
 
 ACROTRETA MICROSCOPICA (SllUmaill ) ({). 693). 
 
 Figures 1, V, 1"; la, la', la"; lb, lb', lb"; and Ic, Ic', Ic". Top, back, and side views of the exterior of four ventral 
 valves illustrating variations in outline, position of the apex, etc. Locality 67, Upper Cambrian 
 limestone, on Tatur Hill, northeast of BiuTiet, Burnet County, Texas. V . S. Nat. Mus. Cat. Nos. 
 52120a, 52120f, 52120b, and 52120c, respectively. 
 
 Id, Id', and Id". Top, back, and side views of a ventral valve from Locality 70e, Upper Cambrian limestone, 
 near Morgans Creek, Burnet County, Texas. L". S. Nat. Mus. Cat. No. 52118a. 
 
 le and Ig. Exteriors of dorsal valves associated with the shells represented by figures 1, la-c. U. S. Nat . Mus. 
 Cat. Nos. 52120d and 52120e, respectively. 
 
 If and Ih. Exteriors of dorsal valves associated with the specimen represented by figure Id. U. S. Nat. Mus. 
 Cat. No. 5211Sb and 52118c, respectively. 
 
 lo, lo', and lo". Top, side, and back ^•iews of the cast of a small ventral valve from Locality 68, Upper Cam- 
 brian limestone, on Packsaddle Mountain, Llano County, Texas. L'. S. Nat. Mus. Cat. No. 52504a. 
 
 2, 2', and 2". Top, back, and side \-iew8 of a ventral valve with an unusually well-defined false area. V. S. 
 Nat. Mus. Cat. No. 521193. 
 
 2a, 2a', and 2a". Top, back, and side views of a ventral valve which has lost the apex and exposed the ft)rami- 
 nal tube. U. S. Nat. Mus. Cat. No. .52119b. 
 
 2b and 2c. Side \-iews of two elevated ventral valves. V. S. Nat. Mus. Cat. Nos. 52119c and 52119d, respec- 
 tively. 
 
 2d. Exterior of dorsal valve with side outline. V. S. Nat. Mus. Cat. No. 52119e. 
 
 The specimens represented by figures 2, 2a-d are all from Locality 8o, Upper Cambrian limestone, 2 miles north 
 of Aurum, Schell Creek Range, White Pine County, Nevada. 
 
 ACROTKETA MICROSCOPICA TETONENSIS Walcott (p. 694). 
 
 , Mus. 
 
 FiGTTRES 3, 3', 3"; 3a, 3a', 3a"; and 3b, 3b', 3b". Top, back, and side views of three ventral valves. U. S. Nat. 
 Cat. Nos. 352S0a, 352S0b, and 35280e, respectively. Figure 3 represents the type specimen. 
 3c and 3d. Exterior \'iews, and outlines showing convexity, of two dorsal valves. V. S. Nat. Mus. Cat. Nos. 
 35280c and 35280d, respectively. 
 
 The specimens represented by figures 3, 3a-d are from Locality 4e, Middle Cambrian limestones in divide at the 
 head of Jackson Creek, Teton Mountains, Wyoming. 
 
 ACROTRETA MICROSCOPICA MISSOTJRIENSIS Walcott (p. 694). 
 
 Figures 4, 4', and 4". Top, back, and side views of the type specimen, a vcniral valve that has been slightly com- 
 pressed longitudinally, thus elevating it, also emphasizing the median furrow on the false area. 
 U. S. Nat. Mus. Cat. No. 35728a. 
 
 4a and 4a'. Top and side views of a ventral valve that has been depressed by compression, the apex being 
 forced backward over the false area. U. S. Nat. Mus. Cat. No. 35278b. 
 
 4b. Exterior of dorsal valve, showing traces of radiating strise and numerous indentations caused by the fine 
 grains of sand in the matrix. V. S. Nat. Mus. Cat. No. 35278c. 
 
 The specimens represented are all froru Locality Ilk. Middle Cambrian shale, St. Francois County. Missouri. 
 226 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL.LXVII 
 
 
 i 1° 
 
 ■1 
 
 ^ 
 
 M 3' 
 
 3' 
 
 
 5'= 5- 
 
 FRANCES W.eSER DEL. 
 
 ^ ^ 
 
 I'- 
 
 ,// 
 
 ^^■ 
 
 ^ 
 
 z<!?^ 
 
 2" 
 
 >1 
 
 %. 
 
 i 
 
 I ■■^... 
 
 3° 
 
 ^rf^»^ 
 
 I 
 
 
 .[, i)> 
 
 \ 
 
 'f 
 
 1 -^i.J^'- J 
 
 5! 
 
PLATE LXVII. 227 
 
 ACROTRETA ARGENTA Walcott (j). 674). 
 
 Figures 5, 5', and 5". Top, bark, and side views of a compressed ventral valve in which the foramina! tube is exposed 
 by the removal of the apex. U. S. Nat. Mus. Cat. No. 52062a. 
 
 5a. Interior of a ventral valve. U. S. Nat. Mus. Cat. No. 52062b. 
 
 5b and 5b'. Cast of a ventral valve that preserves the outline of the visceral cavity and the trapezoidal 
 area that includes the central, outside lateral, and middle lateral muscle scars. It is the type speci- 
 men. U. S. Nat. Mus. Cat. No. 52062c. 
 
 5c. Partly exfoliated dorsal valve. U. S. Nat. Mus, Cat. No. 52062d. 
 
 5d. Top view of a crushed ventral valve. The dark portion preserves the shell. U. S. Nat. Mus. Cat. 
 No. 52062e. 
 
 The specimens represented by figures 5, 5a-d are from Locality 8b', Upper Cambrian arenaceous shales, 1 mile 
 sotithwest of Emigrant Pass, Esmeralda County, Nevada. 
 
 Figures 5e and 5e'. Top and side views of a ventral valve from Locality 7y, Upper Cambrian limestone, 2.5 miles 
 southeast of Emigrant Pass, Esmeralda County, Nevada. U. S. Nat. Mus. Cat. No. 35265a. 
 5f and 5g. Interior and cast of dorsal valves from Locality 7x, Upper Cambrian limestone, 2.5 miles south- 
 east of Emigrant Pass, Esmeralda County, Nevada. U. S. Nat. Mus. Cat. Nos. 35265b and 35265c, 
 respectively. 
 
PLATE LXVIII. 
 
 229 
 
PLATE LXVIII. 
 
 cl. Cardinal scar. s. Median septum or ridge. 
 
 fa. False area. v. Visceral area, 
 
 fp. False pedicle groove. vs. Main vascular sinus. 
 h. Central muscle scar. 
 
 ACROTRETA CTTRVATA Walcott (p. 682). 
 
 F1GURE8 1, r. J"; la, la', la"; and lb, lb', lb". Top, side, and back views of the exterior of ventral valves. U. S. 
 
 Nat. Mils. Cat. Nos. 35269a, 3.5269b, and 35269c, respectively. Figure la represents the type specimen. 
 Ic, le', Ic"; Id, Id', Id"; and le, le', le". Top, side, and back views of casts of the interior of ventral 
 
 valves. U. S. Nat. Mus. Cat. Nos. 35269d, 35269e, and 35269f, respectively. 
 If, Ig, Ih, and li. Exterior and outline of convexity of four dorsal valves. U. S. Nat. Mus. Cat. Nos. 3o269g, 
 
 35269h, 352691, and 35269J, respectively. The specimen represented by figiu-e Ig was figiu'ed by Walcott 
 
 [1884b, PI. I, fig. Id] as Acrotreta gemma. The specimen has been repeatedly figured (see p. 682). 
 Ik and 11. Interiors of two dorsal valves. U. S. Nat. Mus. Cat. Nos. 35269k and 352691, respectively. The 
 
 specimen represented by figure 11 was figured by \Yalcott [1884b, PI. I, fig. le] as Acrotreta gemma. 
 
 The specimen has been repeatedly figured (see p. 682). 
 Ira, Im', Im", and In, In', In". Top, side, and back views of casts of the interior of dorsal valves. U. S. 
 
 Nat. Mus. Cat. Nos. 35269m and 35269n, respectively. 
 
 The specimens represented are all from Locality 203a, passage beds between the Upper Cambrian and the Ordovi- 
 cian, Hamburg Ridge, southwest of Wood Cone, Eureka district, Nevada. 
 
 Acrotreta idahoensis Walcott (]). 687). 
 
 [PI. LXV, figs. 1. la-i] 
 
 Figures 2, 2', 2"; 2a, 2a', 2a"; 2b, 2b', 2b"; and 2c, 2c', 2c". Top, side, and back views of four ventral valves. U. S. 
 Nat. Mus. Cat. Nos. 52089a, 52089b, 52089c, and 52089d, respectively. 
 2d, 2e, and 2f. Exterior and outline of convexity of three dorsal valves. U. S. Nat. Mus. Cat. Nos. 52089e, 
 520891, and 52089g, respectively. 
 
 The specimens represented by figmes 2, 2a-f are from Locality 88a, Middle Cambrian limestone in the northern 
 suburbs of Deadwood, Black Hills, South Dakota. 
 
 Figure 2g. Ventral valve from Locality 165, Middle Cambrian limestone, about 1 mile below the main part of Dead- 
 wood, Black Hills, South Dakota. U. S. Nat. Mus. Cat. No. 52090a. 
 
 Acrotreta lisani Walcott (p. 692). 
 
 Figures 3^ 3a, and 3b. Top, back, and side views of a ventral valve, the type specimen. IT. S. Nat. Mus. Cat. 
 No. 52.50.5a. 
 3c. Exterior of dorsal valve. U. S. Nat. Mua. Cat. No. 52505b. 
 
 The specimens represented by figures 3, 3a-c are from Locality C22, Middle Cambrian, Changhia limestone, at 
 Changhia, Shantung, China. 
 
 230 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH Ll PL. LXVMI 
 
 I 
 
 dl 
 
 I !■ 
 
 I" 
 
 !•' 
 
 (3>. ^ ^- "-g^: iQ 
 
 :(j|P t^< ..fl^. 
 
 I I 
 
 ;>- - 1 
 
 ^, 
 
 J: ^ 
 
 fP.. 
 
 2b- 
 
 1'- 
 
 FRANCES WIESER DEL. 
 
1 
 
PLATE LXIX. 
 
 231 
 
PLATE LXIX. 
 
 cl. CardiDal scar. s. Median septum or ridge, 
 
 h. Central scar. vs. Main vascular sinus. 
 
 ACROTRETA PRIM^VA Walcott (p. 700). 
 
 Figures 1, V, I"; la, la', la"; and lb, lb', lb". Top, side, and back views of three ventral valves. U. S. Xat. 
 
 Mus. Cat. No.s. 15343a, 15342a, and 15342b, respectively. The type specimen, represented by 
 
 figure 1, was figirred by Walcott [188(ib, PL VIII, figs. 1 and la] as Acrolrda gemma. These figures 
 
 have been repeatedly copied (see p. 700). 
 Ic. Exteriorof dorsal valve. U. S. Nat. Mus. Cat. Xo. 15343b. Specimen figured by Walcott[1886b, PI. VIII, 
 
 fig. lb] as Acrolrda gemma. This figure has been repeatedly copied (see p. 700). 
 Id. Cast of the interior of a dorsal valve. U. S. Xat? Mus. Cat. No. 15342c. 
 le, le', and le". Top, side, and back views of a cast of the interior of a ventral valve. U. S. Xat. Mus. 
 
 Cat. No. 15342d. 
 If. Cast of the interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52061a. 
 
 The specimens represented are all from Locality 31a, Lower Cambrian limestone near Pioche, Nevada. 
 
 AcEOTEET,\ PYXiDicuLA White (p. 701). 
 
 Figure 2. Dorsal valve from Locality 313f , I^pper Cambrian limestone at Schellboume, Nevada. U. S. Nat. Mus. 
 Cat. No. 8570a. Specimen figured by White [1877, PI. Ill, figs. 3a-b(?)]. 
 
 2a and 2b. Exterior and outline of convexity of two dorsal valves from Locality 4h, Middle Cambrian lime- 
 stone 4 miles east-northeast of Logan, Gallatin Coimty, Montana. U. S. Nat. Mus. Cat. Nos. 52149a 
 and 52149b, respectively. 
 
 2c, 2c', 2c": 2d, 2d', 2d"; and 2e, 2e'. 2e". Top. side, and back views of tliree ventral valves associated 
 with the dorsal valves represented by figures 2a and 2b. U. S. Nat. Mus. Cat. Nos. 52149c, 52149d, 
 and 52149e, respectively. 
 
 2f, 2f', and 2f". Top, side, and back views of a ventral valve associated with the specimen represented by 
 figure 2. U. S. Nat. Mus. Cat. No. 8570b. Type specimen, figured by White [1877, PI. Ill, figs. 3c 
 and 3d (?)]. 
 
 3, 3', and 3". Top, side, and back views of ventral valve from Locality 6b, Middle Cambrian Langston lime- 
 stone, 2 miles southea,st of Malade, Oneida County, Idaho. U. S. Nat. Mus. Cat. No. 52147a. 
 
 3a, 3a', and 3a". Top, side, and back views of cast of the interior of a ventral valvo associated with the speci- 
 men represented l)y figure 3. V. S. Xat. Mus. Cat. Xo. 521471). 
 
 3b. Top and side views of cast of the interior of a dorsal valve associated with the specimen represented by 
 figure 3, in which the median ridge is slightly developed. U. S. Nat. Mus. Cat. Xo. 52147c. 
 
 3c and 3c'. Top, side, and back views of cast of the interior of a dorsal valve as.sociated with the specimen 
 represented by figure 3, showing strong median ridge and central and cardinal scars. U. S. Nat. 
 Mus. Cat. No. 52147d. 
 
 3d. Exterior and side outline of convexity of a dorsal valve from Locality 322, Middle Camlirian limestone 15 
 miles west of Montpelier, Idaho. IT. S. Nat. 5Ius. Cat. Xo. 52150a. 
 
 3e, 3e', and 3e". Top, side, and back views of a cast of the interior of a ventral valve associated with the 
 specimen represented liy figme 3. U. S. Nat. Mus. Cat. Xo. 52147e. 
 
 3f, 3f', and 3f". Top, side, and back views of the interior of a ventral valve associated with the specimen 
 represented by figiu-e 3d. If. S. Nat. Mus. Cat. Xo. 52150b. 
 
 AcROTRETA SIGNALI.S Walcotl (p. 711). 
 
 Figures 4, 4', and 4". Top, side, and back ■\'iews of a ventral valve, the type specimen, from Locality 328e, Middle 
 Cambrian sandstone at St. Croix Falls, Polk County, Wisconsin. The foraminal aperture of 4" is 
 restored from a second specimen. U. S. Xat. Mus. Cat. Xo. 35285a. 
 232 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LXIX 
 
 M ^^i.^^.. V.^F.1 2' 2'" 
 
 # 
 
 .^r^^ 
 
 1 2°' 
 
 2" 
 
 2«' 2' 
 
 3 
 
 2< 
 
 ,^2^ ri ^iv ..ij I *i, /iv 
 
 i /( 
 
 T 3' 
 
 3«' 
 
 3' 
 
 3" 
 
 4" 
 
 1 
 
 
 
 -^^..-^-i 
 
 FRANCES WIESER DEL. 
 
PLATE LXIX. 233 
 
 ACROTRETA SHANTUNGENSIS Walcott (p. 710). 
 
 Figures 5, 5a, and 5b. Top, side, and hark \-iews of a ventral valve, the type specimen. U. S. Nat. Mus. Cat. 
 No. 52512a. 
 5c. Top view of a ventral valve with the apex broken off. IT. S. Nat. Mus. Cat. No. 52512b. 
 5d. Exterior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52512c. 
 5e. Interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52512d. 
 
 The specimens represented are all from Locality C62, Middle Cambrian limestone 2.5 miles south of Yenchuang, 
 Sintai district, Shantung, China. 
 
 AcROTRETA PACiFicA Walcott (p. 699). 
 
 Fksures 6 and 6a. Top and side views of an elevated ventral valve, the type specimen, from Locality C5, Middle 
 Cambrian limestone 3.2 miles southwest of Yenchuang, Sintai district, Shantung, China. U. S. Nat. 
 Mus. Cat. No. 52506a. 
 
 6b, 6c, and 6d. Top, back, and side views of a ventral valve with pointed apex, associated with the specimen 
 represented by figures 6 and 6a. U. S. Nat. Mus. Cat. No. 52506b. 
 
 6e. Partly exfoliated dorsal valve from Locality C2, Middle Cambrian limestone 2 miles south of Yen- 
 chuang, Sintai district, Shantung, China. U. S. Nat. Mus. Cat. No. 52508a. 
 
PLATE LXX. 
 
 235 
 
PLATE LXX. 
 
 cl. Cardinal scar. vs. Main vascular slnns. 
 
 h. Central scar. x. Cast of foraininal aperture, 
 
 s. Median septum or ridge. 
 
 ACROTBETA SCHMALENSEEI Walcott (p. 709). 
 
 FiGDRE,s 1, 1', and 1". Top, back, and side views of ventral valve. U. S. -Nat. Mus. Oat. No. 182031. 
 
 J a, la', la"; lb, lb', lb"; Ic, Ic', Ic"; and Id, Id', Id". Top, side, and back views of typical forms of the 
 
 ventral valve. U. S. Nat. Mus. Cat. Nos. 18203a-d, respectively. Figure la represents the type 
 
 specimen, 
 le, le', le"; If, If, If"; Ig, Ig', Ig"; Ih, Ih', Ih"; and li, li', li". Top, side, and back views of casts of the 
 
 interior of ventral valves. U. S. Nat. Mus. Cat. Nos. lS203e-i, respectively. 
 lj> Ij', W; Ik, Ik', Ik"; 11, 11', 11"; Im, Im', Im"; In, In', In"; and lo, lo', lo". Top, side, and back 
 
 views of casts of the interior of dorsal valves. U. S. Nat. Mus. Cat. Nos. 18203j-o, respectively. 
 Ip. Cast of the interior of a dorsal valve with a small and short median ridge. U. S. Nat. Mus. Cat. No. 
 
 18203p. 
 Iq and Ir. Exteriors and side outlines of two dorsal valves. U. S. Nat. Mus. Cat. Nos. 18203q and 18203r, 
 
 respectively. 
 Is, Is', and Is". Top, back, and side views of the cast of a ventral valve in which the ijiterior vascular mark- 
 ings are unusually faint for this species. U. S. Nat. Mus. Cat. No. 18203s. 
 
 The specimens represented by figures 1, la-s are from Locality 8w, Middle ('ambrian limestone of the Faradoxides 
 forchhammcri zone at Andrarum, Province of Christ ianstad, Sweden. 
 
 ACROTRETA EGGEGRUNDENSIS Wimail (p. 684). 
 
 Figures 2a, 2b, and 2c. Top, side, and back views of a ventral vahe from Locali)> 311, Middle? Cambrian sandstone 
 bowlder No. 3, on Eggegrund Island, Gefle Bay, Sweden. Type specimen in the collection of the 
 University of Upsala; cast iu the United States National Museum (Cat. No. .57099a). Specimen 
 figured in corresponding positions by Wmian [1902, PI. II, figs. 29, 27, and 20, respectively]. 
 2d. Dorsal valve associated with the ventral valve represented by figiu-es 2a-c. Original in the collection of 
 the University of Upsala; cast in the United States National Museum (Cat. No. •57099b). Specimen 
 figured by Wiman [1902, PI. II, fig. 24]. 
 
 AcROTRETA uPLANDicA Wimao (p. 714). 
 
 Figures 3, 3a and 3b. Top, side, and back views of the type specimen, a ventral valve, from Locality 311b. Middle? 
 Cambrian sandstone bowlder No. 2 on liiludden, near Getle, Sweden. Original in the collection 
 of the Univer.sity of Upsala; cast in the United States National Museum (Cat. No. .57100a). 
 3c. Dorsal valve associated with the specimen represented by figures 3, 3a-b. Original in the collection of 
 the University of Upsala; cast in the United States National ^Museum (Cat. No. .57100b). 
 
 Figures 3, 3a-c are redrawn from the specimens figureil by 'Wiman [1902, PI. II, figs. 15-18, respectively], 
 
 ACROTRETA I'PLAXDICA LlMOENSl.S (Williail) (p. 714). 
 
 Figures 4, 4a, and 4b. Top, side, and back views of the tyi>e specimen, a ventral valve, from Locality 311n, Middle ? 
 Cambrian sandstone bowlder No. fi on Limon Island, Getle Bay, Sweden, Original in the collection 
 of the University of Upsala; cast in the United States National Museum (Cat, No, 57101a), 
 4c. Dorsal valve associated with the specimen represented by figm-es 4, 4a-b. Original in the collection of 
 the University of Upsala; cast in the United States National Museum (Cat. No. 57101b). 
 
 Figures 4, 4a-c are redrawn from the specimens figured by Wiman [1902. PI. II, figs. 19-22] as Acrotreta limoensis. 
 
 236 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LXX 
 
 '^9^__I 
 
 ^ 
 
 !•' 
 
 X 
 
 /^ 
 
 \'' 
 
 
 MELIOTVPE CO BOSTOU 
 
PLATE LXXI. 
 
 237 
 
PLATE LXXI. 
 
 cl. Cardinal scar. v. Visceral area. 
 
 fa. Fal-se area. vs. Main vascular sinus. 
 
 h. Central scar. .\'. Cast of foramin;il aperture. 
 
 s. Median septum. x". Cast of apicalcallosity. 
 
 ACROTRETA SAGITTALIS TACONICA (Walcott) (p. 707). 
 
 Figures 1, 1', and 1". Toj), sido, and back views of a ventral valvo from Locality 37b, Lower Cambrian limestone east 
 
 of Salem, Washington County, New York. U. S. Nat. Mus. Cat. No. .52161a. 
 la, la', and la". Interior of ventral valve associated with the specimen represented by figure 1. IT. S. Nat. 
 
 Mus. Cat. No. 521Glb. 
 lb, lb', lb", and Ic, Ic', Ic". Top, back, and side views of casts of the interior of ventral valves from Locality 
 
 38a, Lower Cambrian limestone south of North Granville, Washington County, New York. U. S. 
 
 Nat. Mus. Cat. Nos. 52163a and 52163b, respective] v. The type specimen, represented by figure Ic, 
 
 was figured by Walcott [1887, PL I, fig. 18b]. 
 Id, Id', and Id". Interior of a ventral valve from Locality 44a, Lower Cambrian limestone on Valatie Kill, 
 
 Rensselaer County, New York. U. S. Nat. Mus. Cat. No. 52165a. 
 le, le', and le". Interior of a ventral valve associated with the specimen represented by figure 1. I". S. 
 
 Nat. MuB. Cat. No. 52161c. 
 If. Dorsal j/alve from Locality 361), Lower Cambrian limestone near Greenwich, Washington County, New 
 
 York. U. S. Nat. Mus. Cat. No. 52166a. 
 Ig. Exterior and outline of convexity of dorsal valve from Locality 22, Lower Cambrian limestone near North 
 
 Granville, Washington County, New York. U. S. Nat. Mus. Cat. No. 52164a. 
 Ih. Exterior and outline of convexity of dorsal valve from Locality 36, Lower Cambrian limestone south of 
 
 Shushan, Washington County, New York. U. S. Nat. Mus. Cat. No. 17441a. Specimen figured by 
 
 Walcott [1887, PL I, fig. 18c]. 
 li and Ij. Casts of the interior and outline of convexity of dorsal valves associated with the specimen repre- 
 sented by figure 1. U. S. Nat. Mus. Cat. Nos. 52161d and 52161e, respectively. 
 Ik. Interior of a dorsal valve associated wnth the specimen represented by figure 1. V. S. Nat. Mus. Cat. 
 
 No. 52161f. 
 11, 11', and Im, Im'. Casts of the interior, with back \-iew and outline of convexity, of two dorsal valves 
 
 associated with the specimen represented by figure 1. V . S. Nat. Mus. Cat. Nos. 52161g and 52161h, 
 
 respectively. 
 In. Cast of the interior and outline of convexity of dorsal \-al\e associated with tlie specimen represented 
 
 by figure 1. U. S. Nat. Mus. Cat. No. 521611. 
 lo. Interior of a ventral valve from Locality 34, Lower Cambrian limestone at Low Hampton, Washington 
 
 County, New York, showing the apical callosity and fine grooves radiating forward from it. U. S. 
 
 Nat. Mus. Cat. No. 52162b. Another specimen (Cat. No. 62163c, Locality 38a) was used to restore 
 
 certain portions of this figure. Specimen figured by Walcott [1887, PI. I, fig. 18a]. 
 
 AcROTRETA SAGITTALIS (Salter) (p. 704). 
 
 Figures 2, 2', 2"; 2a, 2a', 2a"; 2b, 2b', 2b"; and 2c, 2c', 2c". Top, .side, and back views of casts of the interior of four 
 ventral valves from Locality 8w, Middle Cambrian limestones at Andrarum, Province of Christ ianstad, 
 Sweden. U. S. Nat. Mus. Cat. Nos. 52156a, 52156b, 52156c, and 52156d, respectively. 
 
 2d, 2d', and 2f, 2f'. Top and back views of two dorsal valves from Locality 6i, Middle Cambrian limestone 
 near Fosters Point, Random Sound, Newfoundland. U. S. Nat. Mus. Cat. Nos. 521.52a and 52152b, 
 respectively. 
 
 2e and 2e'. Top and back views of dorsal valve from Locality 2s, Middle Cambrian limestones at Hastings Cove, 
 Kennebecasis Bay, St. John County, New Brunswick, Museum?. 
 
 2g. Back view of ventral valve. From Borregaard, Bornholm, Denmark (horizon unknown). Copenhagen 
 LTniversity Museum. 
 
 2h. Back view of cast of dorsal valve. From Borregaard, Bornholm, I>enmark (horizon unknown). Copen- 
 hagen University Museum. 
 
 3, 3', 3", and 3a, 3a', 3a". Top, back, and side views of casta of the interior of ventral valves from Locality 
 318g, Middle Cambrian shales near St. Da\-id8, South Wales. U. S. Nat. Mus. Cat. Nos. 52155a and 
 52155b, respectively. 
 
 3b, 3c, 3d, and 3e. Ventral, side, back, and dorsal views of a cast of the two valves united from Locality 8w, 
 Middle Cambrian limestones at Andrarum, Sweden. U. S. Nat. Mus. Cat. No. 52156e. 
 
 3f. Cast of a ventral valve with truncated apex, associated with the specimen represented by figure 3. V . S. 
 Nat. Mus. Cat. No. 52155c. 
 
 3g, 3g', 3g", and 3h, 3i, and 3j. Casts of the interior of four dorsal valves, with outlines of convexity. Asso- 
 ciated with the specimen represented by figure 3. U. S. Nat. Mus. Cat. Nob. 52155d, 52155e, 52155f, 
 and 521.55g, respectively. 
 238 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LXXI 
 
 
 V 
 
 ) • -1 
 
 2" 
 
 9 
 
 '» 
 
 n 
 
 I.... 
 
 ^ 
 
 •/' < 
 
 2b' 
 
 2S 
 
 </" 
 
 .^^ -'>?». 
 
 2^^^ 
 
 3' 
 
 3'' I 
 
 3«" 
 
 
 4 
 
 !>. 
 
 3 
 
 '•^Hk- 
 
 2" 
 
 )„»>''''* 
 
 3J 
 
 FRANCES WIESER DEL. 
 
 MELIOTVee CO BOSTOM 
 
PLATE LXXII. 
 
 239 
 
PLATE LXXII. 
 
 cl. Cardinal soar. v. Visceral area. 
 
 fa. False area. vs. Main vascular sinus. 
 
 h. Central scar. x'. Cast of foraminal aperture. 
 
 s. Median septum or ridge. x". Cast of apical callosity. 
 
 ACROTKETA SAGITTALIS TRANSVERSA (TIartt) (p. 708). 
 
 Figures 1, 1', 1"; la, la', la"; and lb. Top, side, and back views of casts of interior of three ventral valves. U. S. 
 
 Nat. Mus. Cat. Nos. 52160a, 52160b, and 52160c, respectively. 
 Ic. A ventral valve with a portion of the outer shell. U. S. Nat. Mus. Cat. No. 52160d. 
 Id and Id'. Cast of the interior of dorsal valve, with side view. U. S. Nat. Mus. Cat. No. 52160e. 
 le. le', le"; If, If, If"; and Ig, Ig'. Ig". Top, back, and side views of casts of interior of dorsal valves. 
 
 U. S. Nat. Mus. Cat. Nos. 52160f. 52160g, and 52160h. respectively. 
 Ih, 11, and Ij. Side, dorsal, and back views of a cast of the two valves. U. S. Nat. Mus. Cat. No. 521601. 
 Ik. Interior of a dorsal valve pressed down on a ventral valve. U. S. Nat. Mus. Cat. No. 52160J. 
 
 The specimens represented are all from Locality 3, Upper Cambrian .^haly limestone 300 feet (91.4 m. ) above the 
 Pwadorides zone, Manuels Brook, Conception Bay. Newfoundland. 
 
 ACROTRETA . MISERA (Billillgs) (p. 695). 
 
 Figures 2, 2'. and 2". Top. side, and back \-iews of cast of ventral valve. U. S. Nat. Mus. Cat. No. 52128m. 
 
 2a, 2a', 2a"; 2b, 2b', 2b"; 2c, 2c', 2c"; and 2d, 2d', 2d". Top, side, and back -^iews of casts of ventral 
 
 valves. U. S. Nat. Mus. Cat. Nos. 52128a-d, respectively. 
 2e. 2e'. and 2e". Top. side, and back views of exterior of ventral valve. U. S. Nat. Mus. Cat. No. 52128e. 
 2f and 2g. Exterior and outline of convexity of two dorsal valves. U. S. Nat. Mus. Cat. Nos. 52128f and 
 
 52128g, respectively. 
 2h. Interior of dorsal valve. U. S. Nat. Mus. Cat. No. 52128h. 
 2i, 21', 21"; 2j, 2j', 2j"; 2k, 2k'. 2k"; and 21, 21', 21". Top, side, and back views of casts of the interior of 
 
 dorsal valves. U. S. Nat. Mus. Cat. Nos. 521281-1, respectively. 
 
 The specimens represented are all from Locality 1, Middle Cambrian, shales of zone A of No. 7 of the Manuela 
 Brook section [Walcott, 1891b, p. 261], Manuels Brook, Conception Bay, Newfoimdland. 
 240 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LXXII 
 
 1 ^: 
 
 A' cr 
 
 3 
 
 f 
 
 > 
 
 2b- 
 
 y 
 
 2 
 
 3 
 
 % 
 
 \v 
 
 /"^l^ 
 
 "i; 
 
 2'' 
 
 Zas 
 
 3 
 
 2«' 
 
 M/ 
 
 2' 
 
 r 3, 
 
 €» 
 
 2'' 
 2i" 
 
 ,^2(^1. 
 
 FRANCES WIE3ER DEL. 
 
 MELIOTVPE CO BCSrOM 
 
PLATE LXXIII. 
 
 62667°— VOL 51, pt 2—12 16 241 
 
PLATE LXXIII. 
 
 cl. Cardinal scar. s. Median septum, 
 
 fa. False area. vs. Main vascular sinus, 
 
 fp. False pedicle groove. x'. Cast orforaminal aperture, 
 
 h. Central scar. Jt". Cast of apical callosity. 
 
 AcEOTKETA NiCHOLSONi Davidsoii (p. 696). 
 
 [PI. LXXIII, figs. 6, Ga-b.] 
 
 FiGlTRE 1. Top and side views of a compressed ventral valve, the type specimen. Copied from Davidson [1868, PL 
 XVI, fig. 14]. 
 la and lb. Compressed ventral valves. Copied from Davidson [1871, PI. XLIX, figs. 38 and 39, respectively]. 
 Ic. Exterior of dorsal valve. Copied from Davidson [1868, PI. XVI, fig. 15]. 
 Id. Interior of dorsal valve. Copied from Davddson [1868, PI. XVI, fig. 16]. 
 
 The specimens represented by figm-es 1, la-d are from Locality 316, Lower Ordovician, Upper Lkndeilo? "Black 
 shales" at Dobbs Linn, near Moffat, in Dumfriesshire, Scotland. 
 
 Figures le. It, and Ig. Front, side, and back views of ventral valve, from Locality 316a, Lower Ordovician, Llandeilo, 
 
 at Craighead, Girvan district, AjTshire, Scotland. 
 Ih and li. Back and front views of a ventral valve, from Locality 316a, Lower Ordovician, Llandeilo, at 
 
 Balcletchie, Girvan district, Ayrshire, Scotland. 
 Ij. Exterior of the dorsal valve attached to the specimen represented by figtu-es le. If, and Ig. 
 Ik. Exterior of the dorsal valve attached to the specimen represented by figiu-es Ih and li. 
 
 Figures le-k are copied from Davidson [1883, PL XVI, figs. 21a, 21c, 21b, 22a. 22b, 21d, and 22c, respectively]. 
 AcROTRETA suBCOXicA Kutorga (p. 713). 
 
 Figures 2, 2a-d. Ventral and dorsal valves. Copied from Kutorga [1848, PI. VII, figs. 7a, 7b, 7c, 7b', and 7c', respec- 
 tively]. The specimens represented by figures 2, 2c, and 2d are redrawn in figures 2e, 2h, and 2i, 
 respectively, of this plate. 
 
 2e. Ventral valve. Specimen figured by Kutorga [1848, PI. VII, fig. 7a]. (See fig. 2.) 
 
 2f and 2g. Side and posterior views of the type specimen in Kutorga's collection preserving both ventral 
 and dorsal valves. The dorsal valve shown in these figures is the one figured by Kutorga [1848, 
 PL VII, fig. 7c']. A top view of it is given in figure 2i. 
 
 2h. Posterior view of a ventral valve showing the median groove and pedicle aperture. Specimen figured 
 by Kutorga [1848, PI. VII, fig. 7b']. (See fig. 2c.) 
 
 2i. Dorsal valve shown in side outliae by figures 2f and 2g. Specimen figured by Kutorga [1848, PI. ^'II, 
 fig. 7c']. (See fig. 2d.) 
 
 The specimens represented are from Locality 336, ( )rdovi(ian, Echinosphaeriles limestone, horizon Cla, at Popowka, 
 near St. Petersburg, Russia. 
 
 AcEOTRETA sociALis voii Seebacli (]i. 711). 
 
 Figures 3 and 3a. Side and back views of ventral valve, the type specimen. 
 3b. Interior of ventral valve. 
 3c. Cast of dorsal valve. 
 
 The specimens represented by figures 3, 3a-c are from Locality 334g, Middle Cambrian, Bornholm Island, Den- 
 mark. The figures are copied from von Seebach [1865, PL Villa, figs. 1-4, respectively]. 
 
 Figures 4 4', A", and 4a, 4a', 4a". Top, back, and side views of two ventral valves from Locality 8z. Middle Cambrian 
 limestones of the Paradox-ides alatidicus zone at Borgholm, Oeland Island, Sweden. IT. g. Nat. 
 Mus. Cat. Nos. 35286a and 3528Kb, respectively. 
 4b, 4b', and 4b". Top, back, and side views of a cast of part of the interior of a ventral valve from Locality 
 8w, Middle Cambrian limestones of the ParadoxidfS forchhammeri zone at Andrarum, 20 miles (32 km.) 
 northwest of Simrishanin, Province of Chrislianstad, Sweden. U. S. Xat. Mus. Cat. Xo. 52174a. 
 242 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LXXIII 
 
 |^> C' *^ f 
 
 'M A 
 
 « 
 
 
 • 
 
 I' 
 
 .■^'?^: 
 
 A"- 
 
 i f 
 
 x^ 
 
 FB«NCEe WIESEH DEL. 
 
 5" 
 
 3° 
 
 /%. 
 
 I- 
 
 :^t^i 
 
 I i 
 
 A" 
 
 
 ^. 
 
PLATE LXXIII. 243 
 
 AcROTRETA sociALis voii Seebach — Continued. 
 
 Figures 4c, 4c', 4c", and 4c'". Top, back, side, and front views of a cast of the interior of a ventral valve, showing 
 
 very strong cardinal scars and main vascular sinuses, associated with the shells represented by figures 
 
 4 and 4a. U. S. Nat. Mus. Cat. No. 35286c. 
 4d. Exterior and side views of a dor.sal valve associated with the shells represented by figures 4 and 4a. U. S. 
 
 Nat. Mus. Cat. No. 35286d. 
 4e. Cast of the interior of dorsal valve associated with the shells represented by figures 4 and 4a. U. S. Nat. 
 
 Mus. Cat. No. 3528(ie. 
 
 AcROTRETA SABRING (Callaway) (p. 702). 
 
 Figures 5, 5', and 5". Top, side, and back views of a cast of part of the interior of a ventral valve. U. S. Nat. Mus. 
 
 Cat. No. 57102a. 
 5a, 5a', and 5a". Top, side, and back views of a partly compressed ventral valve. U. S. Nat. Mus. Cat. 
 
 No. 57102b. 
 5b. Cast of the interior of a dorsal valve. Type specimen, figured by Callaway [1877, PL XXIV, fig. 12] ae 
 
 Obolella sabrina;. Collection of Dr. Charles Lapworth. 
 5c. Exterior of a dorsal valve. U. S. Nat. Mus. Cat. No. 57102c. 
 5d. Cast of the interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 57102d. 
 
 The specimens represented are all from Locality 304h, Upper? Cambrian Shineton shales, Mary Dingle, South 
 Shropshire, England. 
 
 AcROTRETA NICH0L80NI Davidson (p. 696). 
 
 [PI. LXXIII, flgs. 1, la-k.] 
 
 Figures 6, 6a, and 6b. Top, side, and back views of cast of ventral valve from Locality 304h, Upper ? ( 'ambrian Shine- 
 ton shales, Mary Dingle, South Shropshire, England. U. S. Nat. Mus. Oat. No. 52131a. 
 
PLATE LXXIV. 
 
 245 
 
PLATE LXXIV. 
 
 a. Area. v. Visceral area, 
 
 cl. Cardinal scar. vs. Main vascular sinus, 
 
 h. Central scar. ^"- Cast of apical callosity, 
 s. Median septum. 
 
 ACROTRETA OPHIRENSIS Walcott (p. 697). 
 
 Figures 1, 1', and 1". Top, side, and back viow.s of ventral valve, the type specimen. U. S. Nat. Mus. Cat. No. 
 
 35281q. 
 la, la', la"; lb, lb', lb"; and Ic, Ic', Ic". Top, side, and back views of ventral valves that illustrate 
 
 variation in form. U. S. Nat. Mus. Cat. Nos. 36281a-c, re.spectively. 
 Id, Id', and Id". Top, back, and side views of cast of interior of a ventral valve. U. S. Nat. Mus. Cat. No. 
 
 35281d. 
 le. Cast of the interior of a ventral valve, showing outlines of visceral cavity. U. S. Nat. Mus. Cat. No. 
 
 35281e. 
 If. Interior of ventral valve with area preserved. U. S. Nat. Mus. Cat. No. 35281f. 
 Ig. Cast of interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 35281g. 
 
 Ih. Cast of part of the interior of a dorsal valve broadened by distortion. U. S. Nat. Mus. Cat. No. 35281h. 
 li. Cast of the interior of a dorsal valve narrowed by distortion. U. S. Nat. Mus. Cat. No. 352811. 
 Ij, Ij', and Ij". Top, side, and back views of exterior of dorsal valve. U. S. Nat. Mus. Cat. No. 35281J. 
 Ik and Ik'. Top and side views of a dorsal valve. U. S. Nat. Mus. Cat. No. 3o281k. 
 1 1. Interior of a dorsal valve. U. S. Nat, Mus. Cat. No. 352811. 
 Im, Im', Im", and In, In', In". Top, side, and back views of casts of interior of elongated dorsal valves. 
 
 U. S. Nat. Mus. Cat. Nos. 35281m and 35281n, respectively, 
 lo. Interior of a finely preserved dorsal valve. U. S. Nat. Mus. Cat. No. 35281o. 
 Ip. Cast of the interior of an undistorted dorsal valve. U. S. Nat. Mus. Cat. No. .3.5281p. 
 
 The specimens represented are all from Locality 3e, Middle Cambrian limestone less than 400 feet (121.9 m.)above 
 the quartzitic sandstones, at Ophir, Oquirrh Range, Tooele County, Utah. 
 
 AcROTRETA OPHIRENSIS RUGOSA Walcott (p. 699). 
 
 Figure 2. Interior of a ventral valve. U. S. Nat. Mus. Cat. No. 35282a. 
 
 2a and 2a'. Top and side views of a ventral valve, the type specimen. U. S. Nat. Mus. Cat. No. 35282b. 
 
 2b and 2b'. Top and side views of a cast of the interior of a ventral valve. U. S. Nat. Mus. Cat. No. 35282c. 
 
 2c and 2c'. Top and side views of a dorsal valve. U. S. Nat. Mus. Cat. No. 35282d. 
 
 2d. Interior of a dor.sal valve. U. S. Nat. Mus. Cat. No. 35282e. 
 
 2e. Cast of interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 35282f. 
 
 The specimens represented are all from Locality 3e, Middle Cambrian limestone less than 400 feet(121.9 m.) above 
 the quartzitic sandstones, at Ophir, Oquirrh Range, Tooele County, Utah. 
 
 AcROTRETA CLAYTONI Walcott (p. 680). 
 
 Figures 3, 3', and 3". Top, side, and back views of a ventral valve from Locality 175, Lower Cambrian shales on the 
 divide between Clayton and Fish Lake valleys, about 15 miles (24.2 km.) south-southwest of the town 
 of Silver Peak, Silver Peak quadrangle (U. S. Geol. Survey), E.smeralda County, Nevada. U. S. Nat. 
 Mus. Cat. No. 52080a. This is the type specimen. 
 
 3a. Partly exfoliated dor.sal valve ai^-sociated with the specimen represented by figure 3. U. S. Nat. Mua. 
 Cat. No. 52080b. 
 
 3b. Cast of interior of a distorted ventral valve from Localily 11, Lower Cambrian limestones of No. 3 of the 
 Silver Peak group [Walcott, 1908f, p. 189], about 2.5 miles (4 km.) south of Barrel Spring, and 0.5 
 mile (0.8 km.) east of the road, in the extreme southeastern corner of the Silver Peak (juadrangle 
 (U. S. Geol. Survey), Esmeralda County, Nevada. U. S. Nat. Mus. Cat. No. 52081a. 
 246 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LXXIV 
 
 X' cl 
 
 i 
 
 ^' *<'* * 
 
 r 
 
 ^fT 
 
 |b' 
 
 ^\\\ 
 
 'i* 
 
 r 
 
 2" 
 
 \t 
 
 3 
 
 
 ^- 
 
 2° 
 
 ,-^f>; 
 
 FRANCES W1E8EH DEL. 
 
 MCLIOTVPE CO BOSTOM 
 
PLATE LXXV. 
 
 247 
 
PLATE LXXV. 
 
 AcROTKETA RUDis Walcott (p. 702). 
 
 [PI. LXV.flg. 3f.] 
 
 Figure 1. Enlargement by photography of a small piece of arenaceous shale on which the casts of three ventral and 
 three dorsal valves have lieen compressed. The ventral valves are crushed and spread out toward 
 the aperture. Locality 121, Middle Cambrian Rogersville shale, road just east of Harlan Knob, 
 4 miles (G.4 km.) northeast of Rogersville [Keith, 1905, areal geology sheet], Hawkins County, Ten- 
 nessee. U. S. Nat. Mus. Cat. No. 52112a. 
 
 ACROTRETA CONULA Walcott (p. 6S1). 
 
 FiGUKE 2. Enlargement by photography of a fragment of shale studded with shells of this species. Locality 310a, 
 Upper Cambrian shales of Olcnus truncatus zone, on Oeland Island. Sweden. U. S. Nat. Mus. Cat. 
 No. 35267a. 
 
 2a. Cast of interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 35267a. 
 
 2b. A vertically compressed ventral valve, the type specimen. U. S. Nat. Mus. Cat. No. 35267a. 
 
 Figure 2a is drawn from the specimen which is partly cut by the lower margin of figure 2, just to the left of the 
 center. Figure 2b is of a specimen from the same slab of shale but outside the limits of figure 2. 
 
 AcROTHYRA PROAViA (Mattliew) (p. 717). 
 
 [PI. LXXVI, figs. 3, 3a-u.] 
 
 FiGCEE 3. Enlargement by photography of a small piece of limestone in which numerous ventral and dorsal valves 
 are embedded. The varying shape of the ventral valves is well illustrated. Locality lOq, Middle 
 Cambrian sandstone below the waterfall in Division E2b of Matthew's [1903, p. 21] Etcheminian, 
 Dugald Brook, Indian River, eastern Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. No. 52052r. 
 248 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LXXV 
 
 ( r- ''^vzj^- 'y. 
 
 :<^T 
 
 
 ^■ 
 
 i'/J^m- ■■■■ /^ 
 
 r in. 
 
 ^4r 
 
 rX' 
 
 
 *^>fA iE« 
 
 ••^ ^ 
 
 >^^-^ 
 
 
 
 f.v V^V ■■■ !„^. •>,■«»■,<;• 
 
 
 ^■;^^^ 
 
 ^r^b 
 
 K 
 
 
 ^^--f'.--'^ 
 
 
 si: V 
 
 
 FRANCES WIESER DEL. 
 
 ELIOTVPE CC eOSTOH 
 
PLATE LXXVI. 
 
 249 
 
PLATE LXXVI. 
 
 cl. Cardinal scar. vs. Main vascular sinus. 
 
 Ip. False pedicle groove. x. Foraminal aperture. 
 
 s. Median septum or ridge. x'. Cast of foraminal tube. 
 
 V. Visceral area. x". Cast of apical callosity. 
 
 AcROTRETA i.NfFLATA (Matthew) (p. 690). 
 
 FiGUEES 1 and V. Top and side views of an unu.sually well-preserved ventral valve, showing radiating lines on 
 
 inner lamellse of the shell. Locality 2f, Middle Cambrian sandstones of Division Ibl of Matthew's 
 
 [1895, p. 108] Protolenus zone, Hanford Brook, St. John County, New Brunswick. U. S. Nat. Mus. 
 
 Cat. No. 3.5276a. 
 la and la'. Top and side views of an elevated ventral valve associated with the specimen represented by 
 
 figure 1. U. S. Nat. Mus. Cat. No. 3527Gb. 
 lb and lb'. Top and side \'iews of a ventral valve associated with the specimen represented by figure 1, 
 
 with the apex broken off so as to show the cast of the large apical callosity and the base of the small 
 
 foraminal tube. U. S. Nat. Mus. Cat. No. 35276c. 
 Ic, Ic', and Ic". Top, side, and back views of a partly exfoliated ventral valve associated with the 
 
 specimen represented by figure 1, showing cast of the large cardinal muscle scars and apical callosity. 
 
 U. S. Nat. Mus. Cat. No. 35276d. 
 Id and Id'. Top and side views of a ventral valve in which the false area slopes forward. Middle Cam- 
 brian sandstones of Di^'ision Ibl (the general horizon of localities 21 and 2g) on Hanford Brook, 
 
 St. John County, New Brunswick. University of Toronto, Canada. (See figure Ig for back view.) 
 le and le'. Top and side views of a broad ventral valve from Locality 2g, Middle Cambrian, in sandstones 
 
 of Division Ibl of Matthew on Hanford Brook, St. John County, New Brunswick, preserving the 
 
 foraminal aperture. U. S. Nat. Mus. Cat. No. 35276e. 
 If, If, and If". Top, side, and back views of a specimen with a relatively small apical callosity and 
 
 vertical false area. Middle Cambrian sandstones of Division Ibl (the general horizon of localities 
 
 2f and 2g) on Hanford Brook, St. John County, New Brunswick. University of Toronto, Canada. 
 Ig. Back view of specimen represented by figure Id, with upper portion restored from another specimen. 
 Ih. Cast of an elongate dorsal valve associated with the shell represented by figure 1. L^. S. Nat. Mus. 
 
 Cat. No. 3.5276f. 
 li. Partly exfoliated dorsal valve associated with the specimen represented by figure le. U. S. Nat. 
 
 Mus. Cat. No. 35276g. 
 Ik and Ik'. Top and back vaews of cast of dorsal valve associated with the specimen represented by 
 
 figure le, showing large cardinal scars and strong median ridge. U. S. Nat. Mus. Cat. No. 35276h. 
 2. Ventral valve from the same general horizon as that of localities 2f and 2g, Middle Cambrian sandstones of 
 
 Division Ibl on Hanford Brook, St. John County, New Brunswick. University of Toronto, Canada. 
 
 Drawn from the type specimen of the species; it was figured by Matthew [1886, PI. V, figs. 7 and 7a] 
 
 as Li/igiilella f inflata. 
 2a. Ventral valve associated with the specimen represented by figure 2. University of Toronto, Canada. 
 
 Specimen figured by Matthew [1895a, PI. V, figs, -i-^-c] aa Lingulella f inflata ovalis. 
 
 AcROTUYRA PROAViA (Matthew) (p. 717). 
 
 [PI. LXXV, fig. 3.] 
 
 Figure 3. Slender, elongate ventral valve from Locality 131, Middle Cambrian shaly sandstones of E3a of Matthew's 
 Etcheminian, Dugald Brook, Cape Breton, Nova Scotia. University of Toronto, Canada. This 
 specimen was first illustrated by Matthew [1901b, fig. 1, p. 303] as Acrothyra pmavia prima. 
 
 3a and 3a'. Top and side views of a ventral valve. U. S. Nat. Mus. Cat. No. 52052a. 
 
 3b. A broader form of the ventral valve than that shown by figure 3. U. S. Nat. Mus. Cat. No. 52052b. 
 
 3c. A ventral valve associated with specimen represented by figure 3. University of Toronto, Canada. 
 
 3d, 3d', and 3d". Top, back, and side views of a ventral valve with the apex broken off. Labeled "A. 
 proavia var.;" it is probably the variety "crassa" Matthew. University of Toronto, Canada. Hori- 
 zon and locality unknown. 
 
 3e and 3e'. Top and side views of a broad ventral valve; this probably represents the form for which 
 Matthew proposed the variety crassa. U. S. Nat. Mus. Cat. No. 52052c. 
 250 
 
U. S. GEOLOGICAL SURVEY 
 
 J 
 
 ^rr- 
 
 I 
 
 ^ 
 
 J 
 
 ''/ 
 
 \ 
 
 \ 
 
 MONOGRAPH LI PL. LXXVI 
 
 1 
 
 4 ^ 
 
 ^ 
 
 ^ 
 
 f^ 
 
 FRANCES WIESEB DEL. 
 
 LIOTVPE CO eOSTOM 
 
PLATE LXXVI. 251 
 
 AcROTHYRA PROAViA (Matthew) — Continued. 
 
 Figure 31". Ventral valve. U. S. Nat. Mus. Cat. No. .52052d. 
 
 3g. Posterior \'iew of false area of a specimen associated with the specimen represented by figure 3. Univer- 
 sity of Toronto, Canada. 
 
 3h. Posterior view of false area of a much broader shell than that represented by figure 3g. U. S. Nat. Mus. 
 Cat. No. 52052e. 
 
 3i, 3k, and 31. Casts of ventral valves showing cast of visceral cavity. U. S. Nat. Mus. Cat. Nos. 62052f, 
 52052g, and 52052h, respectively. 
 
 3m. Interior of a ventral valve. U. S. Nat. Mus. Cat. No. 520521. 
 
 3n. Interior of a ventral valve with the apex broken away. U. S. Nat. Mus. Cat. No. 52052J. 
 
 3o. Two ventral valves illustrating effect of distortion by compression. U. S. Nat. Mus. Cat. No. 52052k. 
 
 3p. Interior of a dorsal valve associated with many specimens of this species, which varies in outline and 
 internal markings from all other specimens. This may be owing to elongation and compression in 
 the matrix. U. S. Nat. Mus. Cat. No. 520521. 
 
 3q. Interior of dorsal valve* U. S. Nat. Mus. Cat. No. 52052m-. 
 
 3r and 3s. Casts of interior of dorsal valves. U. S. Nat. Mus. Cat. Nos. 52052n and 52052o, respectively. 
 
 3t. Interior of dorsal valve. U. S. Nat. Mus. Cat. No. 52052p. 
 
 3u. Exterior and side outline of a dorsal valve. U. S. Nat. Mus. Cat. No. 52052q. 
 
 With the exception of figures 3, 3c, 3d, and 3g, all of the specimens represented by figures 3, 3a-u are from Locality 
 lOq, Middle Cambrian sandstone below the waterfall in Division E2b of Matthew's [1903, p. 21] Etcheminian, Dugald 
 Brook. Indian River, eastern Cape Breton, Nova Scotia. 
 
 AcROTHYRA MINOR Walcott (p. 717). 
 (Text flg. 59, p. 717.) 
 
 FiQUKES 4 and 4'. Top and side views of a nearly perfect ventral valve, the type specimen. U. S. Nat. Mus. Cat. 
 
 No. 52050a. 
 4a and 4a'. Top and aide views of a cast of the interior of a ventral valve that had a large apical callosity. 
 
 U. S. Nat. Mus. Cat. No. 52050b. 
 4b, 4b', and 4b". Top, back, and side views of a cast of the interior of a ventral valve. IT. S. Nat. Mus. 
 
 Cat. No. 52050c. 
 
 The specimens represented are all from Locality 5b, Middle Cambrian Langston limestone near the mouth of 
 Twomile Canyon, 2 miles (3.2 km.) southeast of Malade, Oneida County, Idaho. 
 
PLATE LXXVII. 
 
 253 
 
PLATE LXXVII. 
 
 cl. Cardinal scars. s. Median septum, 
 
 fp. False pedicle groove. vs. Main vascular sinus, 
 
 h. Central scars. x". Cast of apical callosity. 
 
 ACROTRETA CONCENTRICA Walcott (p. 681). 
 
 Figures 1, 1', and 1". Top, side, and back views of the exterior of a ventral valve, the type specimen. U. S. Nat. 
 Mus. Cat. No. 35266a. 
 la and la'. Top and side views of a partial cast of the interior of a ventral valve, showing the base of strong 
 
 vascular sinuses and cardinal scars. U. S. Nat. Mus. Cat. No. 35266b. 
 lb. Cast of a compressed dorsal valve. U. S. Nat. Mus. Cat. No. 35266c. 
 
 The specimens represented are all from Locality 96x, Middle Cambrian limestone 1 mile (1.6 km.) north of Adairs- 
 ville, 15 miles (24.2 km.) northwest of Cartersville, Cartersville quadrangle (U. S. Geol. Survey;, Bartow County, 
 Georgia. 
 
 AcROTRETA BAiLEYi Mattliew (p. 676). 
 
 Figures 2, 2', and 2". Top, side, and back views of a slightly distorted ventral valve. Type specimen, (igiu-ed by Mat- 
 thew [1886, PI. V, figs. 13c and 13d]. This specimen has been repeatedly figured; see page 676 for 
 record. 
 2a. Cast of a distorted dorsal valve. Specimen figured by JIatthew [1886, PI. V, fig. 13]. The specimen has 
 
 been repeatedly figured; see page 676 for record. 
 2b and 2c. Casts of the interior of distorted dorsal valves. 
 2d. Interior of a compressed dorsal valve. 
 The specimens represented are all from Locality 300, Middle Cambrian shaly sandstones, possibly of Di\'ision Id 
 of Matthew, on Long Reach, St. John River. Kings County, New Brunswick. They are in the collection of the Uni- 
 versity of Toronto, Canada. 
 
 AcROTRETA SEEBACHI Wllloott (p. 710). 
 
 Figures 3, 3', and 3". Top, back, and side views of a cast of the interior of a ventral valve from Locality 8x, 
 
 passage beds between the L^pper Cambrian and the Ordovician, Ccratopyge limestone at the cement 
 
 works at Slemmestad, about 3 miles (4.8 km. t .southwe.'^t of Christiania, Norway. U. S. Nat. Mus. 
 
 ' Cat. No. 52172a. This is the type specimen. 
 
 3a, 3a', and 3a". Top, side, and back views of the exterior of a ventral valve associated with the .specimen 
 
 represented l)y figure 3. U. S. Nat. Mus. Cat. No. 52172b. 
 
 AcROTRETA PARVULA (Wallerius) (p. 699). 
 
 Figures 4, 4', and 4". Top, back, and side views of ventral vahe from Locality 3101. pa.ssage beds between the Mid- 
 dle and Upper Cambrian, in limestone at Borgholm, Oeland Island, Sweden. U. S. Nat. Mus. Cat. 
 No. 35283a. 
 4a. Exterior of dorsal valve, associated with the specimen represented by figure 4. V. S. Nat. Mus. ("at. 
 No. 35283b. 
 
 AcROTRETA GEMMULA MattllCW (p. 686). 
 
 [PI. LXVI, figs. 3. 3a-c.] 
 
 Figures 5, 5', and 5". Top, back, and side views of the exterior of a ventral valve from Locality lOp. Middle Cam- 
 brian sandstones of Division E2b of Matthew's Etcherainiaii on Dugald Brook. Indian River. Cape 
 Breton. Nova Scotia. U. S. Nat. Mus. Cat. No. 52088a. 
 
 5a, 5a', and 5a". Top, back, and side views of a ventral valve showing the cast of the surface of the apical 
 callosity. Locality lOp", Middle Cambrian sandstone on the small brook on the hill between the 
 bridge over Indian River and McPhees Brook, Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. 
 No. 52088b. 
 
 5b, 5b'. and 5b". Top, back, and side views of a ventral valve a.ssocialed witli the specimen represented 
 by figure 5, showing cast of base of vascular sinuses, surface of apical callosity, and pedicle tube. 
 U, S. Nat. Mus. Cat. No. 52088c. 
 254 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LXXVII 
 
 O 3 
 
 \ 
 
 ga' 
 
 1 
 
 FBANCE6 WIESER OEt. 
 
 HELIOTVPC CO BOSTC 
 
PLATE LXXVII. 255 
 
 AcROTRETA GEMMULA Matthew — Continued. 
 
 FiQWRBS 5c and 5c'. Top and side views of a ventral valve associated with the specimen represented by figure 5, 
 
 that has a more erect posterior side than most specimens. U. S. Nat. Mus. Cat. No. 52088d. 
 5d and 5d'. Back and side views of a ventral valve associated with the specimen represented by figure 5, 
 
 the surface of which has lieen roughened by the impress cjf the fine grains of sand in the matrix so 
 
 that it resembles the surface characteristic of " Acrotreta papiUulu^' MatUhevi^Acrothyra sera. U. S. 
 
 Nat. Mus. Cat. No. 52088e. 
 5e. Side view of a ventral valve associated with the specimen represented by figure 5. in which the posterior 
 
 side curves backward a.s in Matthew's figure of the ventral valve [1903, PI. Ill, fig. 4b]. U. S. Nat. 
 
 Mus. Cat. No. 52088f. 
 5f and 5f'. Top and side views of thcexterior of a dorsal valve associated with the specimen represented by 
 
 figure 5. U. S. Nat. Mus. Cat. No. 52088g. 
 
 Acrotreta babel Barrande (p. 676). 
 
 Figures 6 and 6a. Top and side views of a ventral valve, the type specimen, from Locality 303, Lower Ordovician, 
 Etage d3 at Konigshof, Bohemia. Copied from Barrande [1879b, PI. XCV, figs, vii; 2A and 2B, 
 respectively]. 
 6b. Cast of dorsal valve associated with specimen represented by figures (i and 6a. Copied from Barrande 
 [1879b, PI. XCV, fig. vu: 2C]. 
 
 Acrotreta? minima (Barrande) (p. 695). 
 
 Figure 7. Top view of ventral \ alve, the type specimen, from Locality 303d, Lower Ordovician, Etage dl at Swarow, 
 Bohemia. 
 7a. Cast of dorsal valve associated with the specimen represented by figure 7. 
 
 The figures are both copied from Barrande [1879b. PI. XCV, figs, ii; 3A and lA, respectively], who labeled 
 them "Obolus f minimus." 
 
 Acrotreta belti (Davidson) (p. 678). 
 
 Figure 8. Cast of the interior of a compressed ventral valve, the type specimen, from Locality 306, LTpper Cambrian 
 Lower Tremadoc shales at Craig-y-dinas, North Wales. 
 8a. Cast of the interior of a dorsal valve associated with the specimen represented by figure 8. 
 
 The figures are both copied from Davidson [1871. PL L. figs. 16a and 17a, respectively]. The same specimens 
 were figiu-ed by Davidson [1868, PI. XV, figs. 27a and 26a, respectively], both as Oholdla bdti. 
 
 Acrotreta neboensis Walcott (p. 695). 
 
 Figure 9. Top view of ventral valve. U. S. Nat. Mus. Cat. No. 52130a. 
 
 9a, 9a', and 9a". Top, side, and back views of the exterior of a ventral valve, the type specimen. U. S. Nat. 
 
 Mus. Cat. No. 52130b. 
 9b. Exterior of a dorsal valve, showing strong median sinus. U. S. Nat. Mus. Cat. No. 52130c. 
 
 The specimens represented are all from Ix)cality 14t, Middle Cambrian limestone in Mount Nebo Canyon, 3 miles 
 (4.8 km.) southeast of Mona, Juab County, Utah. 
 
 Acrotreta nox Walcott (p. 696). 
 
 Figures 10 and 10'. Top and side views of a ventral valve, the type specimen, from Locality lOv, Upper Cambrian 
 shales at Fox Glen, about 8 miles (12.8 km.) east of Baraboo, Sauk County, Wisconsin. U. S. Nat. 
 Mus. Cat. No. 52132a. 
 
PLATE LXXVIII. 
 
 62667°— VOL 51, pt 2—12 17 257 
 
PLATE LXXVIII. 
 
 ac. Apical callosity. h. Central muscle scar, 
 
 cl. Cardinal scar. s. Median septum. 
 
 fa. False area. vs. Main vascular sinus. 
 
 (p. False pedicle groove. x". Cast of apical callosity. 
 
 ACROTRETA OPIIIRENSIS DESCEXDEXS Walcott (p. 698). 
 
 Figures 1, V, and 1". Top, side, and back views of ventral valve, the type specimen. U. S. Nat. Mus. Cat. No. .52143a. 
 Copied from Walcott [1908d, PI. IX, figs. 1, 1', and 1"]. 
 la. Posterior portion of ventral valve showing apex. U. S. Nat. Mus. Cat. No. 52143d. 
 lb. Dorsal valve. U. S. Nat. Mus. Cat. No. 52143c. 
 Ic. Interior of a dor.sal valve. U. S. Nat. Mus. Cat. No. 52143b. Copied from Walcott [1908d, PI. IX, fig. la]. 
 
 The specimens represented are all from Locality 30n, Middle Cambrian limestone in Ic of the Weeks limestone, on 
 the north side of Weeks Canyon, about 4 miles south of Marjum Pass. House Range [Walcott, 1908f, PI. XIII], Millard 
 County, Utah. 
 
 AcROTRETA MARJUJIEXSIS Walcott (p. 693). 
 
 Figures 2, 2', and 2". Top, side, and back views of ventral valve, the type specimen, from Locality lln. Middle 
 Cambrian limestone in la of the Marjum limestone in the long cliff 2 mUes (3.2 km.) southeast of 
 Marjum Pass, Hou.se Range, Utah. U. S. Nat. Mus. Cat. No. .52116a. Copied from Walcott [1908d, 
 PI. IX, figs. 2, 2', and 2"]. Two specimens, both on the same hand specimen as the shell represented 
 by figure 2, were also used in drawing these figures. 
 
 2a. Top \ie\v of a nearly circular ventral valve from Locality 33d, Upper-Cambrian limestone at the base of 
 the first high point southwest of the J. J. Thomas ranch, Fish Spring Range, LTtah. U. S. Nat. Mus. 
 Cat. No. 52117a. 
 
 2b. Broken dorsal valve associated with the specimen represented by fig:ure 2. U. S. Nat. Mus. Cat. No. 
 521 16c. Another specimen (Cat. No. 52116e) was used to restore certain portions of this figure. 
 
 2c. Interior of dorsal valve associated with the specimen represented by figure 2. U. S. Nat. Mus. Cat. No. 
 52116b. Copied from Walcott [1908d, PI. IX, fig. 2a]. 
 
 2d. Side view of median septum of a dorsal valve associated with the specimen represented by figure 2. L'. S. 
 Nat. Mus. Cat. No. 52116d. 
 
 ACROTRETA ULRICHI Walcott (p. 71-1). 
 
 Figures 3, 3', and 3". Top, side, and back views of ventral valve from Locality 12p, Upper Cambrian limestones of 
 the Reagan sandstone, at the northwest extremity of the Arbuckle Mountains, about 4 mUes (6.4 km.) 
 east of Homer, Carter County, Oklahoma. I^. S. Nat. Mus. Cat. No. 52180a. Copied from Walcott 
 [1908d, PL IX, figs. 3, 3', and 3"]. This is the type specimen. 
 
 ACROTRETA BELLATULA Walcott (p. 077). 
 
 FiGURE.s 4, 4', and 4". Top, side, and back views of ventral valve, the type specimen. U. S. Nat. Mus. Cat. No. 
 
 52072a. Copied from Walcott [1908d, PI. IX, figs. 4, 4', and 4"j. 
 4a. Extcriorof dorsal valve. U. S. Nat. Mus. Cat. No. 52072e. 
 4b. Portion of interior of ventral valve. U. S. Nat. Mus. Cat. No. o2072b. Copied from Walcott [1908d, PL 
 
 IX, fig. 4a.] 
 4c. Cast of interior of ventral valve. U. S. Nat. Mus. Cat. No. 52072d. 
 4d. Cast of interior of dorsal valve. V. S. Nat. Mus. Cat. Xo. .52072c. Another specimen (catalogue No. 
 
 520721) was used to restore certain portions of this figure. Copied from Walcott [1908d, PL IX, fig. 4b]. 
 
 The specimens represented are all from Locality lOz, Middle Cambrian limestones in la of the Marjum limestone 
 in the long cliff southeast of Marjum Pass [Walcott, 190Sf, p. 179, and Pis. XIII and XV], House Range, Utah. ■ 
 258 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LXXVIII 
 
 I 
 
 s:^ ^ 
 
 ^- d if); 
 
 f^ 
 
 y 
 
 ^ 
 
 2" 
 
 2" 
 
 'Y 
 
 2" 
 
 3" 
 
 ac cl _3' 
 
 m > 
 
 4' 
 
 4" 
 
 6"' 
 
 (1 
 
 X 
 
 7^ 
 
 8" 
 
 -'I 
 
 8" 
 
 
 A 
 
 FRANCES WIESEH DEL. 
 
 MeVlOIVPE CO BOSTON 
 
PLATE LXXVIII. 259 
 
 LiNNARSSONELLA GIRTYI Walcott (p. 666). 
 [PI. LXXIX, figs. 1, la-r.) 
 
 Figures 5 and 5'. Top and side views of ventral valve from Locality 32t, Ujjper Cambrian limestone in Fandango 
 Spring Canyon on the east side of the Dugway Range, about 5 miles (8 km.) north of where the stage 
 road between Vernon and Deep Creek crosses the divide, Tooele County, Utah. U. S. Nat. Mus. Cat. 
 No. 52195a. 
 5a. Exterior view of dor.sal valve associated with the specimen represented by figure 5. U. S. Nat. Mus. Cat. 
 No. 52195b, 
 
 LiNNARSSONELLA TRANSVERSA Walcott (p. 670). 
 
 Figures 6, 6', and 6". Top, side, and back views of ventral valve from Locality 30j, Upper Cambrian limestone in le 
 of the Orr formation on Orr Ridge, about 5 miles (8 km.) south of Marj'um Pass [Walcott, 1908f, p. 176 
 and PI. XIII], House Range, Utah. U. S. Nat. Mus. Cat. No. 52201a. Figures 6 and 6' are copied 
 from Walcott [1908d, PI. IX, figs. 6 and 6']. This is the type specimen. 
 6a, 6b, and 6c. Partly exfoliated dorsal valves associated with the specimen represented by figure 6. U. S. 
 Nat. Mus. Cat. Nos. 52201b, 52201c, and 52201d, respectively. 
 
 LiNNARSSONELLA NITENS Walcott (]). 669). 
 
 Figures 7, 7', and 1" . Top, side, and back views of \-entral valve from Locality 31t, Upper Cambrian limestone in Id 
 of the Orr.formation on Orr Ridge, about 5 miles (8 km.) south of Marjum Pass [Walcott lOOSf, p. 176 
 and PI. XIII], House Range, Utah. U. S. Nat. Mus. Cat. No. 52198a. Figures 7 and T are copied 
 from Walcott [1908d, PI. IX, figs. 7 and 7']. This is the type specimen. 
 7a. Partly exfoliated dor.sal valve associated with the specimen represented by figure 7. U. S. Nat. Mus. 
 Cat. No. 52198b. 
 
 LiNNARSSONELLA MODESTA Walcott (p. 66.S). 
 
 Figures 8, 8', and 8". Top, side, and back views of ventral valve from Locality 31t, Upper (.'ambrian limestone in 
 
 Id of the Orr formation on Orr Ridge, dbout 5 miles (8 km.) south of Marjum Pass [Walcott, 1908f, p. 
 
 176and PI. Xlll], House Range, Utah. U. S. Nat. Mus. Cat. No. 53G79a. Figures 8 and 8' are copied 
 
 from Walcott [190Sd, PI. IX, figs. 8 and 8']. 
 8a. A more acuminate ventral valve than that represented by figure 8. U. S. Nat. Mus. Cat. No. 52197e. 
 8b and Sb'. Exterior and back views of a partly exfoliated ventral valve. U. S. Nat. Mus. Cat. No. 52197b. 
 8c and 8d. Partly exfoliated ventral valves. U. S. Nat. Mus. Cat. Nos. 52197c and 52rj7d, respectively. 
 8e. Interior of ventral valve, the type specimen. U. S. Nat. Mus. Cat. No. 52197a. Copied from Walcott 
 
 [1908d, PI. IX, fig. 8a]. 
 8f. Interior of dorsal valve. U. S. Nat. Mus. Cat. No. 52197f. 
 
 The spei'imens represented by figures 8a-f are from Locality 30k, 25 feet below Locality 31t (fig. 8), at the same 
 place on Orr Ridge. 
 
 LiNNARSSONELLA URANIA Walcott (p. 670). 
 
 Figure 9. Partly exfoliated dorsal valve. U. S. Nat. Mus. Cat. No. 52202d. 
 
 9a, 9a', and 9a". Top, side, and back views of a partly exfoliated ventral valve. U. S. Nat. Mus. Cat. No. 
 
 52202a. Figure 9a is copied from Walcott [1908d, PL IX, fig. 9]. This is the type specimen. 
 9b. Interior of ventral valve. U. S. Nat. Mus. Cat. No. 52202c. 
 9c. Interior of dorsal valve. U. S. Nat. Mus. Cat. No. 52202b. Copied from Walcott [1908d, PL IX, fig. 9a]. 
 
 The specimens represented are all from Locality 55u, Middle Cambrian limestone 0.25 mile (0.4 km.) below the 
 Maxfield mine, in Big Cottonwood Canyon, on the west side of the Wasatch Mountains, southeast of Salt Lake City, Utah. 
 
PLATE LXXIX. 
 
 261 
 
PLATE LXXIX. 
 
 a. Central lateral space of area, 
 a'. Outer lateral space of area, 
 ol. Cardinal scar. 
 
 f. Flexure lino of an'u. 
 fa. False area. 
 h. Central muscle scar. 
 
 j. Anterior lateral muscle scar. 
 
 s. Median septum or ridge. 
 
 V. Visceral area, 
 vs. Main vascular sinus. 
 
 X. Foraminal aperture, 
 x". Cast of apical callosity. 
 
 LiNNARSSONELLA GIRTYI AValcott (\). 666). 
 [Pi. LXXVIII, figs. 6, 5a.] 
 
 Figure 1. Exterior of ventral valve with side \-iew of same, the type specimen. U. S. Nat. Mus. Cat. No. 35287a. 
 la, la', and la". Exterior, posterior, and side views of ventral valve. The archini; of the cardinal line of the 
 
 area is well shown in this shell. U. S. Nat. Mus. Cat. No. 352.S7q. 
 lb and lb'. Exterior, side, and posterior views of ventral valve. The straight, horizontal cardinal lino of the 
 
 area is a feature of this shell. U. S. Nat. Mus. Cat. No. 35287b. 
 Ic and Ic'. Exterior, with side and posterior views, of ventral valve with nearly straight cardinal line of shell 
 
 and area. U. S. Nat. Mus. Cat. No. 35287c. Compare the outline and slope of the area in this speci- 
 men with that showTi in figures 1 and la . 
 Id and lo. Exterior and side ^■iew^ of two ventral valves. U. S. Nat. Mus. Cat. Nos. 3.5287d and 35287e, 
 
 respectively. 
 If-lj. Exterior and side views of dorsal valves, to illustrate variation in outline and convexity of valve. U. S. 
 
 Nat. Mus. Cat. Nos. 35287f-j, respectively. ■ 
 Ik. Cast of interior of ventral valve with side outline. I". S. Nat. Mus. Cat. No. 35287k. 
 Ik'. Posterior view of specimen represented by figure Ik, showing po.sterior outline of cardinal scars and the 
 
 vascular canals; also base of cast of foramen. U. S. Nat. Mus. Cat. No. 35287k. 
 1 1. Cast of the interior and side outline of a dorsal valve. This illustrates all that is known of the interior 
 
 of this valve from the casts. An interior from another locality is shown by figure Ir. U. S. Nat. 
 
 Mus. Cat. No. 3.5287 1. 
 Im-lp. Casts of the interior and side outlines of ventral valves that illustrate the variation in size and position 
 
 of the cardinal scars and ^•ascular canals. U. S. Nat. Mus. Cat. Nos. 35287m-p, respectively. 
 
 The specimens represented by figures 1, la-p are from Locality 88a, Middle Cambrian limestone about 100 feet 
 (30.5 m) above the quartzilic sandstone at the base of the Cambrian, in the northern suburbs of Deadwood, Black 
 Hills, South Dakota. 
 
 FiGtjREs Iq, Iq', and Iq". Top, side, and back views of exterior of ventral valve that is more elevated than usual 
 and which has a very high false area. U. S. Nat. Mus. Cat. No. 52188a. 
 Ir. Interior of dorsal valve on which the area is preserved, also the depressions of the cardinal scars and a 
 low, broad, median ridge, but no traces of the central or anterior lateral scars. This is the only speci- 
 men found showing the interior of the valve, except in the form of casts (fig. 1 1). V . S. Nat. Mus. 
 Cat. No. 52188b. 
 
 The specimens represented by figiures Iq and Ir are from Locality 9p, Upper Cambrian, about IfiO feet (48.8 m) 
 above the porphyry contact in the lunestone of the Reagan sandstone, in SE. \ NE. J sec. 2, T. 4 N., R. 13 W., about 
 15 miles (24.2 km.) northwest of Fort Sill, Comanche County, Oklahoma. 
 
 LiNNARSSONKLLA MiNUTA (Hall and Whitfield) (p. 667). 
 
 Figure 2. Interior of a ventral valve, showing cardinal scars and foramen. V . S. Nat. Mus. Cat. No. 24553a. 
 
 2a and 2a'. Cast of the interior of a ventral valve with side and ixisierior outlines. U. S. Nat. Mus. Cat. No. 
 
 24553b. 
 2b. Cast of the interior of a dorsal valve and side view of game. U. S. Nat. Mus. Cat. No. 24553c. 
 
 The specimens represented are all from Locality 313h, T'pper Cambrian sandy shale on Hamburg Ridge, Eureka 
 district, Nevada. They all occur on the same hand specimen wilh the shells reprosenlcd by Hall and ^\■hitlield [1877, 
 PI. I, figs. 3 and 4], but the latter shells, which include the type, are not figured in this monograiih. 
 262 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LXXIX 
 
 ^^.^'^'■'.■^! .3P,«I 
 
 i/^ 
 
 J^ 
 
 
 f'W ;J* 
 
 (Q 
 
 ,^-^^fci. 
 
 // 
 
 -!.«:^-J- I' 
 
 2' 
 
 1/ 
 
 
 r*]| 
 
 l^ 
 
 avx 
 
 ^ 
 
 I'' 
 
 Jf 
 
 -^r^z^ 
 
 3" 
 
 / 
 
 s. 
 
 I ^ 
 
 1l 
 
 '|A 
 
 '^..1 
 
 FRANCES WIESEH DEL. 
 
 MELIOirPE CO BOSTOW 
 
PLATE LXXIX. 263 
 
 LiNNARSSONELLA TENNESSEENSIS Walcott (p. 669). 
 
 Figures 3 and 3'. Exterior and side views of a ventral valve from I^ocality 13, Middle Cambrian limestones of the 
 Rome formation 1.5 miles (2.4 km.) east of Post Oak Springs [Hayes, 1S94, areal geology sheet], Roane 
 County, Tennessee. U. S. Nat. Mus. Cat. No. 35289a. This is the type specimen. 
 
 3a. Cast of the exterior of a ventral valve from Locality 107b, Middle Cambrian shales in the Rome formation 
 in Bull Run, northwest of Copper Ridge [Keith, 1896b, areal geology sheet], 11 miles northwest of 
 Knoxville, Tennessee. U. S. Nat. Mus. Cat. No. 3528Sa. 
 
 3, 3b', and 3c, 3c'. Top and back views of casts of ventral valves associated with the specimen represented 
 by fig. 3. U. S. Nat. Mus. Cat. Nos. 35289b and 35289c, respectively. 
 
 3d, 3e, 3f, and 3g. Casts of the interior of ventral valves associated with the specimen represented by figure 
 3a. U. S. Nat. Mus. Cat. Nos. 352S8b, 35288c, 35288g, and 3528Sh, respectively. Figures 3f and 3g 
 (with fig. 3k) represent the specimens that were referred to Meehina prima (see p. 669). 
 
 3h, 3j, and 3k. Casts of interior of dorsal valves associated with the specimen represented by figure 3a. U. S. 
 Nat. Mus. Cat. Nos. 352S8d, 35288e, and 352881, respectively. Another specimen (Cat. No. 35288f) 
 was used to restore certain portions of this figure. Figures 3k, 3f, and 3g represent the forms 
 that were refen-ed to Meekina prima (see p. 669). 
 
 3i. Cast of interior of dorsal valve associated with the specimen represented by figure 3. U. S. Nat. Mus. 
 Cat. No. 35289d. 
 
 ACROTRETA SPINOSA Walcott (p. 713). 
 
 Figures 4, 4', and 4". Top, side, and back views of a ventral valve. V. S. Nat. Mus. Cat. No. 52176a. 
 
 4a. Top view of a ventral valve, with the apex in front of the posterior margin. U. S. Nat. Mus. Cat. No. 
 
 52176b. 
 4b. Top view of a ventral valve, the type specimen, with the apex overhanging the posterior margin, and 
 
 showing spinose surface. V . S. Nat. Mus. Cat. No. 5217Gc. 
 4c. Exfoliated ventral valve, showing cast of the apical callosity and main trunks of the vascular sinuses. 
 
 U. S. Nat. Mus. Cat. No. 52176d. 
 4d. Exfoliated ventral valve from Locality 62, Upper Cambrian limestone in the Dunderberg shale [W'alcott, 
 
 1908f, p. 184], in canyon immediately north of Adams Hill, Eureka district, Nevada. V . S. Nat. Mus. 
 
 Cat. No. 52177a. 
 4e. Cast of interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52176e. 
 4f. Exterior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52176f. (See fig. 4g.) 
 4g. Enlargement of the surface of the specimen represented by figure 4f, to illustrate spinose character of 
 
 the outer shell. IT. S. Nat. Mus. Cat. No. 52176f. 
 
 With the exception of figure 4d, the specimens represented are all from Locality 61, Upper Cambrian limestone 
 in the Dunderberg shale, a little south of the Hamburg mine. Eureka district, Nevada. 
 
 AcROTRETA?? CANCELLATA Walcott (p. 679). 
 
 Figures 5 and 5'. Top and side \dews of the type specimen, a ventral valve, from Locality 205, passage beds between 
 the tapper Cambrian and the Ordovician, siliceous limestones on Round top Mountain, Eureka dis- 
 trict, Nevada. U. S. Nat. Mus. Cat. No. 52079a. 
 5a. Enlargement of outer surface (X20) of the specimen represented by figure 5. 
 
 ACROTRETA ATTENTJATA Meek (p. 675). 
 
 [PI. LXIV, flgs. 1, la-o.] 
 
 Figure 6. Interior of a ventral valve. U. S. Nat. Mus. Cat. No. 52068a. 
 6a. Interior of a ventral valve. U. S. Nat. Mus. Cat. No. .5r206Sb. 
 
 The specimens represented are both from Locality 3x, Middle Cambrian limestone in Id of the Marjum limestone, 
 2.5 miles (4km.) east of Antelope Springs, in ridge east of Wheeler Amphitheater, House Range, Utah. 
 
PLATE LXXX. 
 
 265 
 
PLATE LXXX. 
 
 cl. rardinal scar. v. Visceral area. 
 
 fa. False area. v.s. Main va-scular sinus. 
 
 fp. False pedicle irroove. x'. fast of foraminal tube. 
 
 AcROTiiYRA sioxATA Matthew (p. 719). 
 
 Figure 1. Ventral valve from Locality 344k, Middle Cambrian sandstones of Division Elb of Matthew's Etcheminian, 
 . Dugald Brook, Cape Breton, sliowing cast of visceral area. University of Toronto, Canada. Type 
 specimen, figured by Matthew [1902b, PI. XIII, fig. 2b]. 
 
 la. Broad form of ventral valve from Locality lOp, Middle Cambrian sandstones of Division E2b of Matthew, 
 on Dugald Brook, Indian River, Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. No. 520.57a. 
 
 lb. Compressed, nearly circular ventral valve associated with the specimen represented by figure la. U. S. 
 Nat. Mus. Cat. No. 52057b. 
 
 Ic. Partly exfoliated dorsal ^ah-e from Locality lOp, Middle Cambrian sandstones of Division E2b of Mat- 
 thew, on Dugald Brook, Indian River, Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. No. 52057c. 
 
 Id. Side outline of a ventral valve from the locality represented by figure 1. University of Toro.ito, Canada. 
 Specimen figured by Matthew [1902b, Pi. XIII, fig. 2c]. 
 
 ACROTHYRA SIGNATA PRIMA llattliew (p. 720). 
 
 Figure 2. Ventral valve showing cast of visceral area. University of Toronto, Canada. Type specimen, figured by 
 Matthew [1902b, PI. XIII, fig. lb]. 
 2a. Top, side, and back views of a narrow form of ventral valve. U. S. Nat. Mus. Cat. \o. 52059a. 
 2b. Side outline of a ventral valve. University of Toronto, Canada. Sp->cimen figured by Matthew [1902b, 
 PI. XIII, fig. Ic]. 
 The specimens represented are all from Locality 13k. Middle Cambrian shales of Matthew's Coldbrook, on Dugald 
 Brook, Indian River, Cape Breton, Nova Scotia. 
 
 AcROTHYRA SIGNATA ORTA Matthew (p. 719). 
 
 Figure 3. Exterior \'iew of ventral valve from Localit>- 13d", Middle Cambrian sandstones between Di\-isions E2a 
 and E2b of Matthew's Etcheminian, on Dugald Brook, Cape Breton, Nova Scotia. U. S. Nat. Mus. 
 Cat. No. 5205Sa. 
 3a. A broken shell showing cast of visceral area from Locality 3441, Middle Cambrian sandstones of 
 Division E2c of Matthew's Etcheminian, Dugald Brook, Cape Breton. University of Toronto, 
 Canada. Type specimen, "figured by Matthew [1902b, PI. XIII, fig. 4a]. 
 3b. Side outline^of a ventral valve from the locality represented by figure 3a. University of Toronto, 
 Canada. Specimen figured by Matthew [1902b, PI. XIII, fig. 4c]. 
 
 ACROTHYRA SERA (Mattliew) (p. 718). 
 
 Figure 4. Ventral valve, somewhat compressed, from Locality 13t", Middle Cambrian sandstones of Division Elcand 
 
 Eld on Dugald Brook, Cape Breton, Nova Scotia. L". S. Nat. Mus. Cat. No. 52054a. 
 4a, 4a', and 4a". Top, side, and back views of a typical form of ventral valve associated with the specimen 
 
 represented by figure 4. U. S. Nat. Mus. Cat. No. 52054b. 
 4b. Interior of a dorsal valve (locality unknowTi). University of Toronto, Canada. 
 4c. Side outline of a ventral valve from Locality 344g, Middle Cambrian shales of Division Elc of Matthew's 
 
 Etcheminian, Dugald Brook, Cape Breton. L'niversity of Toronto, Canada Specimen figured by 
 
 Matthew [1902b, PI. XIII, fig. 3c] as Acrothyra (siffnata) sera. 
 5, 5', and 5". Top, .side, and back views of ventral valve associated with tlic s])ecimen represented by figure 4. 
 
 U. S. Nat. Mus. Cat. No. 52054c. 
 5a. Ventral valve a,ssociated with the specimen represented by figure 4, showing cast of \-isceral area. U. S. 
 
 Nat. Mus. Cat. No. 52054d. 
 5b. Interior of ventral valve showing elevated ridge about foraminal tube. Locality lOp, Middle Cambrian 
 
 sandstone in Di\-i8ion E2b on Dugald Brook, Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. 
 
 No. 58306. 
 266 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL.LXXX 
 
 / 
 
 2 
 
 4 
 
 6 
 6 
 
 7« 7 
 
 -^ - - I 
 
 FRANCES WiESER DEL. 
 
 3 «' 
 
 r- 
 
 'V 
 
 
 //i 
 
 6" 
 
 3 
 
 3' 
 
 4«' 
 
 /i 
 
 i 
 
 e"' 6' 
 
 6"' 
 
 '% 
 
 68 
 
 5° 
 
 >a 
 
 HtLiorvce . 
 
PLATE LXXX. 267 
 
 AcROTHYRA SERA Matthew — Continued. 
 
 Figure 5c. Cast of interior of a shell associated with the specimen represented by figure 4 showing cast of foraminal 
 tube. U. S. Nat. Mus. Cat. No. 52054e. 
 5d. Exterior of dorsal valve associated with the specimen represented by figure 4. U. S. Nat. Mus. Cat. No. 
 52054f. 
 
 Figures 5, 5a-d are drawn from typical forms of Acrothyra signata tarda of Matthew. 
 
 Figures 6, 6', and 6". Top, side, and back views of a ventral valve from Locality 13k, Middle Cambrian, shales of 
 Matthew's Coldbrook, Dugald Brook, Cape Breton. University of Toroulo, Canada. Specimen 
 figured by Matthew [1902b, PI. XV, figs. 2a and 2b] as Acrolreia papillala. 
 
 6a. Ventral valve with apex of shell broken away so as to show the cast of the foraminal tube, a.ssociated with 
 the specimen represented by figure 4. U. S. Nat. Mus. Cat. No. 52054g. 
 
 6b and 6b'. Dorsal valve with side outline. U. S. Nat. Mus. Cat. No. 52054h. 
 
 6c. Cast of interior of dorsal valve. Compare with figure 4b. U.S. Nat. Mus. Cat. No. 52054i. 
 
 6d and 6d'. Top and side views of a cast of the interior of a ventral valve with elongate visceral area. U. S. 
 Nat. Mus. Cat. No. 520.54J. 
 
 6e. Interior of a ventral valve with elongate \'isceral area. U. S. Nat. Mus. Cat. No. 520.54k. 
 
 6f, 6g, and 6h. Ventral valves illustrating variation in form and length of visceral area. V . S. Nat. Mus. Cat. 
 Nos. 520541, 52054m, and 52054n, respectively. 
 
 6i. Ventral valve from Locality 13k, Middle Cambrian, shales of Matthew's Coldbrook, on Dugald Brook, Cape 
 Breton, Nova Scotia. V. S. Nat. Mus. Cat. No. 52055c. 
 
 The specimens represented by figures 6, 6a-i are typical forms of "Acrotrela papiUata" of Matthew. With the 
 exception of figures 6 and 6i all of the specimens are from Locality 13t", Middle Cambrian .sandstones of Di\'isions Elc 
 and Eld of Matthew on Dugald Brook, Cape Breton, Nova Scotia. 
 
 Figures 7 and 7a. Top and side views of a ventral valve associated with the specimen represented by figure 6i. U. S. 
 Nat. Mus. Cat. No. 520.55a. 
 7b. Exterior of dorsal valve associated with the specimen represented by figure 6i. U. S. Nat. Mus. Cat. 
 No. 52055b. 
 The specimens represented by figures 7, 7a-b are typical furms of "'Acrotrela papillala prima " of Matthew. 
 
 Figures 8, 8', and 8". Top, back, and side views of a shell somewhat doubtfully referred to this species from Locality- 
 13p, Middle Cambrian sandstones 40 feet above division E2a of Matthew, on Dugald Brook, Cape Bre 
 ton, Nova Scotia. U. S. Nat. Mus. Cat. No. 52056a. 
 
PLATE LXXXI. 
 
 269 
 
PLATE LXXXI. 
 
 a. Cardinal area. pc. Pedicle furrow. 
 
 cf. Closed forainiiial tube (see p. t'i29). pi. rialform. 
 
 cl. Cardinal scar. pi'. Central ridge o( platform, 
 
 h. Central mu.scle scar. s. Median ridge. 
 
 i. Transmedian muscle scar. t. Cardinal process of dorsal valve (see p. 505). 
 
 j. Anterior lateral muscle scar. vs. Vascular sinus. 
 
 Ik. Outside and middle lateral muscle scars. x. Cavity beneath platform. 
 m. Muscle scars on front face of platform. 
 
 ScHizoPHOLis RUGOSA Waageii (p. 609). 
 
 [PI. I, fig. 4c.] 
 
 Figures 1, la, and lb. Top, side, and back views of the tj-pe specimen, a ventral valve. Geol. Survey India Cat. 
 No. 3/790. Specimen figured by Waagen [1885, PI. LXXXVI, figs. 4a-d; and 1891, PI. II, figs. 12a-c]. 
 Ic. Exterior \-iew of dorsal valve. Geol. Survey India Cat. No. 3/789. Specimen figured by Waagen [1885, 
 PL LXXXVI, figs. 3a-b; and 1891, PI. II, figs. 14a-b]. 
 
 The specimens represented are all from Locality 357c, Middle Cambrian, lower portion of the ■' Neobolus beds" of 
 the Khussak group, in purplish-colored, fine-grained, micaceous sandstone near the fresh-water springs in a gorge above 
 the salt mines at Kiura (Khewra), Salt Range, India. 
 
 Neobolus warthi Waagen (p. 566). 
 
 [Text figs. 4TA-B, p. SG7, and PI. I, figs. 3, 4.4a-b, 5, and 5a.] 
 
 Figure 2. View of a partly exfoliated ventral valve. Geol. Survey India Cat. No. 3/783. Specimen figured by 
 
 Waagen [1885, PI. LXXXV, figs. 3a-b; and 1891, PL II, figs. 3a-b]. 
 2a. Compressed ventral valve. Geol. Survey India Cat. No. 3/787. Specimen figured by AVaagen [1885, 
 
 PL LXXXVI, figs, la-b] as Davidsonella squama, and [1891, PI. II, figs. 6a-b] as Neobolus icarthi. 
 2b and 2c. Side and back views of a ventral valve showing supposed foraminal aperture. (See p. 566.) 
 
 This shell is on the same piece of rock as the dorsal valve represented by figure 2d. 
 2d. Exterior view of dorsal valve. Geol. Survey India Cat. No. 3/784. Specimen figured by Waagen [1885, 
 
 PL LXXXV, figs. 4a-b; and 1891, PL II, figs. 4a-b]. 
 2e. View of the interior of a ventral valve. Geol. Survey India Cat. No. 3/786. Specimen figured by Waagen 
 
 [1885, PL LXXXV, fig. 5; and 1891. PL II. fig. 3c]. 
 2f. View of the interior of a dorsal valve, the type specimen. Geol. Survey India Cat. No. 3/785. Specimen 
 
 figured by Waagen [1885, PL LXXXV, fig. 5; and 1891. PL II, fig. 4c]. 
 2g. Enlargement of the posterior portion of figure 2f. 
 2h. Front view of the process and platform shown in figure 2g. 
 
 The specimens represented are all from Locality 367a, Middle Cambrian, lower portion of the "Neobolus beds" 
 in purplish, fine-grained, micaceous sandstone at Jutdna, Salt Range, India. 
 
 DisciNOLEPis GRANULATA Waagen (ji. 664). 
 
 Figure 3. Exterior \-iew of tlie typo specimen, a ventral valve, from Locality 367a Middle Cambrian, lower portion 
 of the " Neobolus beds'' in purplish, fine-grained, micaceous sandstone at Jutdna, Salt Range. India. 
 Geol. Survey India Cat. No. 3/792. Specimen figured by Waagen [I8S5. PL LXXXVI. figs, (ia-b; 
 and 1891, PL II, figs. IGa-b]. 
 3a and 31>. Rack and side views of a ventral valve from Locality 367c, Middle Cambrian, lower portion of tlie 
 " A'^rofto/»sbeds"inpurpli.sh, fine-grained, micaceous sandstone near the fresh-water springsina gorge 
 above the salt mines at Kiura (KhewraV Salt Range. India. Geol. Survey India Cat. No. 3/791. The 
 triangular space shown in figure 3a is not filled in with the shell; it is an open slit. Specimen figured 
 by Waagen [1885, PI. LXXXVI, figs. 5a-b; and 1891. PL II, figs. 15a-b]. 
 270 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LXXXI 
 
 FRANCES WIESER DEL. 
 
PLATE LXXXI. 271 
 
 Keyserlingia buchi (de Verneuil) (p. 628). 
 
 Figure 4. Exterior view of a fragmentary ventral valve. U. S. Nat. Mus. Cat. No. 52049a. (See figs. 4b and 4c.) 
 4a. Interior view of the posterior portion of a ventral valve. U. S. Nat. Mus. Cat. No. 52049d. 
 4b. Interior of the posterior portion of the specimen represented by figure 4. 
 4c. Posterior view of the specimen represented by figures 4 and 4b. 
 4d. Interior view of the posterior portion of a ventral valve in which the pedicle tube pr(]jeil,s and opens toward 
 
 the front of the valve. U. S. Nat. Mus. Cat. No. 52049b. 
 4d' and 4d". Side and front views of specimen represented by figure 4d. 
 4e. Interior of the posterior portion of a dorsal \-alve. U. S. Nat. Murj. Cat. No. 52049c. 
 
 The specimens represented are all from Locality 9d, Upper Cambrian Obolus sandstone at Jaggowal, about 20 
 miles (32 km.) east-southeast of Reval, Government of Esthonia, Russia. 
 
 SiPHONOTRETA VERRUCOSA (Eicliwaltl) (p. 627). 
 
 Figures 5, 5a, and 5b. Ventral, dorsal, and side views of a specimen having the two valves united. U, S. Nat. Mus. 
 Cat. No. 52217a. From Locality 337m, passage beds IxHween the Upper Cambrian and the Ordo- 
 ■ vician, Orthoceratitc limestone at Popowka, near St. Petersburg, Russia. 
 
 SiPHONOTRETA UNGUICULATA (Eichwal(l) (}). 626). 
 
 Figures 6 and 6a. Ventral and dor.sal views of a shell having the two valves united, from Locality 337m, passage beds 
 
 between the Upper Cambrian and the Ordovician, Orlhoccratite limestone at Popowka, near St. 
 
 Petersbui-g, Russia. U. S. Nat. Mus. Cat. No. 52218a. 
 6b. Side view of the specimen represented by figures 6 and 6a. 
 6c. Interior of posterior portion of ventral valve, showing opening of pedicle tube and the muscle scars. Copied 
 
 from Davidson [1877, PI. II, fig. 9]. 
 6d and 6e. Interior of dorsal and ventral valves, respectively. From a ca.st of a natural mold of a specimen 
 
 which has the two valves united and which is from the same locality as the specimen represented by 
 
 figures G, 6a-b. U. S. Nat. Mus. Cat. No. 52218b. 
 
 SiPHONOTRETA? DUBIA Walcott (p. 62.5). 
 
 Figures 7 and 7a. Top, side, and posterior views of ventral valves from Locality Iv, Lower Cambrian shales of No. 3 
 of the Silver Peak group [\\'alcott, 19081, p. 189], 3 miles (4.8 km.) north of Valcalda Spring and 4 
 miles (6.4 km.) west-northwest of the Drinkwater mine. Silver Peak quadrangle (U. S. Geol. Survey), 
 Esmeralda County, Nevada. U. S. Nat. Mus. Cat. Nos. 52215a and 52215b. Figure 7 represents the 
 type specimen. 
 7b. Exterior view of a fragmentary dorsal valve associated with the specimens represented by figures 7 and 7a. 
 U.-S. Nat. Mus. Cat. No. 52215c. 
 
 Orbiculoidea varians (Barrande) (p. 72.3). 
 
 FIGURE 8. Ventral valve from Locality 303c, passage beds between the irpper Cambrian and Ordovician, suburbs of 
 Hof, Bavaria, X J. Copied from Barrande [1868a, fig. 71]. This is the type specimen. 
 
 Orbiculoidea contraria (Barrande) (p. 722). 
 
 Figure 9. Ventral valve from Locality 303c, passage beds between the Upper Cambrian and the Ordovician. suburbs 
 o-' Hof, Bavaria, X J. Copied from Barrande [1868a, fig. 72]. This is the type specimen. 
 
 Philhedra COLUMBIAN-^ (Walcott) (p. 724). 
 
 Figures 10 and 10'. Summit and back views of the t\^)e specimen. Locality 14s, Middle Cambrian 0<jii(jopsis zone, 
 on Mount Stephen, al)ove Field, British Columbia. U. S. Nat. Mus. Cat. No. 58307. Copied from 
 Walcott [1908c, PI. I, figs. 5 and 5a]. 
 
272 PLATE LXXXI. 
 
 Orbiculoidea piLEOLUs (Hicks MS.) (Salter) (p. 722). 
 
 FioiRE 11. Exterior of ventral valve, the type specimen, from Locality 318d, Middle Cambrian, Menevian Band- 
 stones at Porth-y-rhaw, St. Davids, South Wales. Copied from Davidson [18G8, PI. XVI, fig. 11a]. 
 11a. Exterior of dorsal valve from the locality represented by figure 11. Copied from Davidson [1868, PI. 
 XVI, fig. 12a]. 
 
 ACROTHELE LEVISENSIS Walcott (p. 646). 
 
 Figure 12. Exterior of a compressed ventral valve, the type specimen. Geol. Survey Canada. Copied from Walcott 
 [1908d, PI. VIII, fig. 13]. 
 12a. Exterior of a compressed dorsal valve. Geol. Survey Canada. 
 12b. Cast of the interior of a dorsal valve. Geol. Survey Canada. 
 
 The specimens represented are all from Locality 319a, Lower Ordo%'ician Levis shales at Point Le\ds, Quebec, 
 Canada. 
 
PLATE LXXXII. 
 
 62e67°— VOL 51, PT 2—12 18 273 
 
PLATE LXXXII. 
 
 cl. Cardinal scar. F'. Cast of foranilnal tube. 
 
 F. Foramen. vs. Vascular sinuses. 
 
 YORKIA WANNEKI Walcott (p. 612). 
 
 Figure 1. Exterior of a corrugated ventral valve, drawn from a cast of a natural matrix. U. S. Nat. Mus. Cat. No. 
 
 26433]. 
 la. Exterior and side outline of a smooth ventral valve, drawn from a cast of a natural matrix. U. S. Nat. 
 
 Mus. Cat. No. 26433a. Specimen figured by Walcott [1897b, PI, LX, fig. ]]. 
 lb. Top view, back view, and side outline of an elevated ventral valve, drawn from a cast of a natural matrix. 
 
 U. S. Nat. Mus. Cat. No. 26433b. 
 Ic. Top and back views of cast of the interior. U. S. Nat. Miis. Cat. No. 26433c. Specimen figured by Walcott 
 
 [lS97b, PI. LX, fig. la]. 
 Id. Exterior of a dor.sal valve, drawn from a cast of a natural matrix. U. S. Nat. Mus. Cat. No. 26433d. 
 le. Cast of the interior of the posterior portion of a ventral valve. U. S. Nat. Mus. Cat. No. 26433e. 
 If and Ig. Casts of the interiors of ventral valves, with side outlines of same. U. S. Nat. Mus. Cat. Nos. 26433f 
 
 and 26433g, respectively. The specimen represented by figure Ig, the type, was figured by Walcott 
 
 [1897b, PL LX, figs, lb and Ic]. 
 Ih. Cast of the interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 26433h. Specimen figured by Walcott 
 
 [1897b, PI. LX, fig. Id], 
 li. Area of dorsal valve drawn from the cast of a natural mold (original specimen missing). U. S. Nat. Mus. 
 
 Cat. No. 26433i. Specimen figured by Walcott [1897b, PI. LX, fig. le]. 
 
 The specimens represented are all from Locality 49, Lower Cambrian sandstone on Codorus Creek, near Emigsville, 
 York County, Pennsylvania. 
 
 YoRKIA? WASHIXGTOXENSIS Walcott (p. 613). 
 
 Figure 2. Cast of the interior of a ventral valve from Locality 37b, Lower Cambrian limestone 0.25 mile (0.4 km.) east 
 of Salem, Washington County, New York. U. S. Nat. Mus. Cat. .No. 26434a. Type specimen 
 figured by Walcott [1897b, PI." LX, fig. 3]. 
 2a. Cast of the interior of a dorsal valve from Locality 338n, Lower Cambrian, western belt of conglomeratic 
 limestone, Rensselaer County, New York. V. S. Nat. Mus. Cat. No. 52207a. 
 
 YoRKIA ? ORIENTALIS Walcott (p. 612). 
 
 Figures 3 and 3'. Top and side views of ventral valve from Locality C71, Middle Cambrian limestone in Kichou 
 formation [Willis and Blackwelder, 1907, pp. 139 and 145], 4 miles (6.4 km.) southwest of Tungytl, 
 Shansi, China. U. S. Nat. Mus. Cat. No. 52521a. This is the type specimen. 
 3a. Enlargement of the outer surface of the specimen represented by figure 3. 
 
 YoRKiA ? MiQUELi AYalcott (p. 611). 
 
 Figure 4. Exterior of ventral valve from Locality 342a, Lower Ordovician?, barren f|uartzitic beds at Coulouma, 
 Department of H6rault, France. This is the type specimen. Collection of J. Miquel. 
 
 DisciNOPSis GULiELMi (Matthew) (p. 720). 
 
 Figure 5. A compressed ventral valve. Type specimen, figured by Matthew [1886, PI. V, figs. 14c and 14dJ. 
 
 5a and 5b. Interiors of ventral valves. Figure 5a is drawn from the specimen figured by Hall and Clarke 
 [1892a, PI. Ill, fig. 21, and 1892c, PI. Ill, figs. 21 and 22]. Figures 5a and 5b are drawn from speci- 
 mens among those figured by Matthew [1886, PI. V, figs. 14, 14a-b, and 14e], but closer identification 
 is impossible. 
 
 5c. Interior of a dorsal valve. Specimen figured by Hall and Clarke [18920, PI. Ill, fig. 23]. Its identifica- 
 tion with any of the figures given by Matthew [1886, PI. V, figs. 14, 14a-b, and 14e] is impossible. 
 
 The specimens represented are all from Locality 301g, Middle Cambrian sandstones of Division Ic of Matthew at 
 Portland, now a part of the city of St. John, St. John County, New Brunswick. They are in the collection of the 
 University of Toronto, Canada. 
 274 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LXXXK 
 
 FRANCES WIESER DEL. 
 
 rt-iOTYPE CO BOSTON 
 
PLATE LXXXII. 275 
 
 , DisciNOPsis? suLCATus Walcott (p. 721) . 
 
 Figure 6. Cast of the interior of a ventral ? valve, the type specimen, from Locality C66, Upper Cambrian Chaumitien 
 limestone at Pagoda Hill, 1 mile (1.6 km.) west of Tsinan, Shantung, China. U. S. Nat. Mus. Cat. 
 No. 52522a. 
 
 Dearbornia clarki Walcott (p. 614). 
 
 Figures 7 and 7a. Exteriors of ventral valves. U. S. Nat. Mus. Cat. Nos. 52214a and 52214b, respectively. Figure 
 7, that of the type specimen, is copied from Walcott [1908d, PI. VIII, fig. 7]. 
 7b. Cast of the interior of a ventral valve. U. S. Nat. Mus. Cat. No. 52214c. 
 7c. Cast of the interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52214d. 
 7d. Exterior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52214e. 
 
 The specimens represented are all from Locality 9k, Middle Cambrian limestone forming Ic of the Dearborn River 
 section [Walcott, 1908f, p. 201], eastern part of the Lewis and Clark National Forest, Montana. 
 
 Trematobolus excelsis Walcott (p. 617). 
 
 Figure 8. Top view, with outline of side and back views, of a cast of a ventral valve, the type specimen. U. S. Nat. 
 Mus. Cat. No. 52208a. Copied from Walcott [1908d, PI. VIII, fig. 8]. 
 8a and 8b. Top view, with outline of side and back views, of exteriors of ventral valves. U. S. Nat. Mus. 
 Cat. Nos. 52208b and 52208c, respectively. 
 
 The specimens represented are all from Locality 53, Lower Cambrian sandstones in the lower portion of 3d of the 
 Waucoba Springs section [Walcott, 19081, pp. 187 and 18S], 1 mile (l.G km.) east of Saline Valley road about 2.5 miles 
 (4 km.) east^ortheast of Waucoba Springs, Inyo County, California. 
 
PLATE LXXXIII. 
 
 277 
 
PLATE LXXXIII. 
 
 cl. Cardinal scar. ' s. Median septum. 
 
 F'. Cast of foraminal tul)e. v. Visceral area. 
 
 h. Central muscle scar. vs. Vascular sinuses. 
 
 j. Anterior lateral muscle scarL 
 
 Trematobolus kempanum (Matthew) (p. 619). 
 
 Figure 1. Exterior of a ventral valve, showing elongate slit into which the foramen opens, drawn from a oast of a 
 
 natural matrix. U. S. Nat. Mus. Cat. No. 52212a. 
 la. A dorsal valve associated with the specimen repre.sented by figure 1, drawn from a cast of a natural matrix. 
 
 U. S. Nat. Mus. Cat. No. 52212b. 
 lb. A crushed ventral valve from Locality 308g, Middle ( ambrian shales of Division lb.3 or lb4 of Matthew's 
 
 section on Long Island [Matthew, 1898a, pp. 124 and 127], Kennebecasis Bay, St. John County, 
 
 New Brunswick. LTniversity of Toronto, Canada. 
 Ic and Id. Casts of the interiors of ventral valves. U. S. Nat. Mus. Cat. Nos. 52212c and 52212d, respectively, 
 le. Cast showing cast of the foraminal tube; the dark portion represents the thickness of the shell. U. S. 
 
 Nat. Mus. Cat. No. 52212e. 
 It. Cast of the interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52212f. 
 
 Ig. Natural cast of the interior of a ventral valve. U. S. Nat. Mus. Cat. No. 52212g. (See fig. Ij.) 
 Ih. Fragment showing the thickened shell on the posterior jiortion of a shell associated with the specimen 
 
 represented by figure lb. LTniversity of Toronto, Canada. 
 li. Cast of the interior of a ventral valve. U. S. Nat. Mus. Cat. No. 52212h. 
 Ij. Interior of a ventral valve drawn from a cast of the specimen represented by figure Ig. U. S. Nat. Mus. 
 
 Cat. No. 52212i. 
 Ik. Enlarged view of a cast of the interior of a ventral valve. U. S. Nat. Mus. Cat. No. 52212J. 
 1 1. Partly exfoliated dorsal valve. U. S. Nat. Mus. Cat. No. 52212k. 
 Im. Cast of the interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52212 1. 
 
 In. Interior of a broken ventral valve drawn from a cast of a natural mold. U. S. Nat. Mus. Cat. No. 52212m. 
 lo. Fragment of the interior of a dorsal valve, showing the peculiar median septum. U. S. Nat. Mus. Cat. 
 
 No. 52212n. 
 
 With the exception of figures lb and Ih, all of the specimens represented are from Locality 2u, Middle Cambrian, 
 lowest beds exposed on the south side of Long Lsland [Matthew, 1898a, pp. 124 and 127], Kennebecasis Bay, St. John 
 County, New Brunswick. 
 
 Trematobolus pristinus (Mattliew) (p. 621). 
 
 [PI. L.\.\.\IV, fig. 6.] 
 
 FiQUEE 2. Exterior of a ventral valve from Locality 21, Middle Cambrian sandstones of Division lb3 of Matthew on 
 Hanford Brook, St. John County, New Brunswick. U. S. Nat. Mus. Cat. No. 52213a. 
 
 2a. Interior of a ventral valve associated with the specimen represented by figure 2. U. S. Nat. Mus. Cat. 
 No. .52213b. 
 
 2b. Interior of a ventral valve associated with the specimen represented by figure 2. U. S. Nat. Mus. Cat. 
 No. 52213c. 
 
 2c. Natural cast of the interior of the ventral valve represented by figure 2b. U. S. Nat. Mus. Cat. No. 52213d. 
 
 The specimens represented by figures 2b and 2c are counterparts; another specimen (Cat. No. 56955b, from Locality 
 2h) was used in drawing both figures. 
 
 FiQURE 2d. Cast of the interior of a dorsal valve from Locality 2h, Middle I ambrian sandstones of Division lb2 of 
 
 Matthew on Hanford Brook, St. John County, New Brunswick. U. S. Nat. Mus. Cat. No. 56955a. 
 2o. Exterior andside views of a dorsal valve from Locality 301, Middle Cambrian sandstones of Division lb2 
 
 of Matthew on Hanford Brook, St. John County, New Brunswick. Original in the collection of the 
 
 University of Toronto, Canada; cast in the United States National Museum (Cat. No. 58308). 
 2f. Cast of the interior and side view of dorsal valve as-sociated with the specimen represented by figure 2e. 
 
 University of Toronto, Canada. Type specimen, figured by Matthew [isn5a, PI. IV, fig. Ic] as Obolus 
 
 pristinus. 
 2g. Cast of the interior of a dorsal valve associated with the specimen represented by figure 2e. University 
 
 of Toronto, Canada. 
 2h. Broken cast of interior of dorsal valve, with side outline, associated with the specimen represented by 
 
 figure 2e. University of Toronto, Canada. 
 278 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL.LXXXIII 
 
 .' ■.^. 
 
 "k..^^ 
 
 \ 
 
 z- 
 
 i^^ 
 
 \ \ 
 
 
 I. 
 
 ^^ 
 
 ^ 
 
 
 ■^ vvtESEP OEt. 
 
 tPC COBCSTON 
 
PLATE luXJOny 
 
 279 
 
PLATE LXXXIV. 
 
 F. Foramen. 
 
 F'. Cast otforaminnl tube, 
 g. Umbonal muscle scars. 
 h. Central muscle scar, 
 i. Transmedian muscle scar, 
 j. Anterior lateral muscle scar. 
 
 p. Cast of false pedicle furrow, 
 pf. Underside of pedicle furrow. 
 
 s. Median septum. 
 
 t. Teeth, 
 vs. Vascular sinus. 
 
 SCHIZAMBON TYPICALIS Walcott (p. 624). 
 
 Figure 1. Exterior of ventral valve. U. S. Nat. Mus. Cat. No. 24556a. 
 
 la. Interior of ventral valve, the type specimen. U. S. Nat. Mus. Cat. No. 24556b. 
 
 lb. Exterior of dorsal valve. U. S. Nat. Mus. Cat. No. 24556c. 
 
 Ic. Interior of dorsal valve. TJ. S. Nat. Mus. Cat. No. 24556d. 
 
 Id. A portion of the surface enlarged to show the minute surface spines. U. S. Nat. Mus. Cat. No. 24556e. 
 
 The specimens represented are all from Locality 201a, Lower Ordovician Pogonip limestone on east slope of ridge 
 east of Hamburg Ridge, Eureka district, Nevada. The figiu-es (1, la-d) are copied from Walcott [1884b, PL I, 
 figs. 3a, 3, 3c, 3b, and 3d. respectively]. 
 
 ScHiZAMBON PRiscus Matthcw (p. 623). 
 
 Figures 2 and 2'. Exterior and side views of ventral valve from Locality 3q, Upper Cambrian shale in Barachois Glen, 
 
 4 miles (6.4 km. ) south of Little Bras d'Or Lake, Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. No. 
 
 52226a. 
 2a. Exterior of ventral valve associated with the specimen represented by figure 2. 
 
 52226b. 
 2b. Interior of ventral valve associated with the specimen represented by figure 2. 
 
 52226c. 
 2c. Interior of a broken dorsal valve from Locality 101, Upper Cambrian shale on east bank of Barachois River, 
 
 6 miles (9.6 km.) from Little Bras d'Or Lake, Cape Breton, Nova Scotia. U. S. Nat. Mus. Cat. No. 
 
 52227a. 
 2d. Interior of a dorsal valve associated with the specimen represented by figure 2c. 
 
 52227b. 
 2e. Interior of a dorsal valve associated with the specimen represented by figure 2. 
 
 52226d. 
 
 U. S. Nat. Mus. Cat. No. 
 U. S. Nat. Mus. Cat. No. 
 
 U. S. Nat. Mus. Cat. No. 
 U. S. Nat. Mus. Cat. No. 
 
 SCHIZAMBON MANITOUENSIS Walcott (p. 623). 
 
 Figure 3. Exterior of a ventral valve, the type specimen. U. S. Nat. Mus. Cat. No. 52224a. 
 3a. Exterior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52224b. 
 3b. Cast of interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52224c. 
 3c. Interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52224d. 
 
 3d. Outline of posterior portion of cast of the interior of a ventral valve. U. S. Nat. Miuj. Cat. No. 52224e. 
 3e. Outline of posterior portion of interior of a ventral valve. U. S. Nat. Mus. Cat. No. 52224f. 
 
 The specimens represented by figures 3, 3a-c are from Locality 186a, and those represented by figures 3d and 3e 
 from Locality 186, a slightly lower horizon; both near the line between the red and gray Ordovician limestone in red 
 limestone of Lower Ordovician age, Williams Canyon, Manitou, El Paso County, Colorado. 
 
 SCHIZAMBON? ESTHONIA Walcott (p. 622). 
 
 Figures 4 and 4'. Exterior and side view of the type specimen, a ventral valve, from Locality 336h, Upper Cambrian 
 Ungulite grit, at Baltischport, Esthonia, Russia. U. S. Nat. Mus. Cat. No. 52222a. 
 280 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH Li PL. LXXXIV 
 
 
 FRANCES W1ESER DEL. 
 
 M-Liorvpe CO aosrox 
 
PLATE LXXXIV. 281 
 
 Trematobolus iNSiGNis Mattliew (p. 617). 
 
 Figure 5. Natural cast, of the interior of a ventral valve. UniverBity of Toronto, Canada. Type specimen, figured 
 
 by Matthew [1893a, (ig. lb, p. 270], (See fig. 5a.) 
 5a. Cast taken from the natural mold of the interior of the ventral valve represented by figure 5. U. S. Nat. 
 
 Mus. Cat. No. 52211a. 
 5b. Interior of a ventral valve. University of Toronto, Canada. Specimen figured by Matthew [189.3a, fig. la, 
 
 p. 276]. (See fig. 5c.) 
 5c and 5c'. Top and back views of an artificial cast of the interior of the ventral valve represented by figure 5b. 
 
 U. S. Nat. Mus. Cat. No. 52211b. 
 
 The two specimens represented are both from Locality 301, Middle Cambrian sandstones of Division lb2 of Matthew 
 [1895a, p. 108], on Hanford Brook, St. John County, New Brunswick. 
 
 Trematobolus pristinus (Matthew) (p. 621). 
 
 [PI. LXXXIII, figs. 2, 2a-h.I 
 
 Figure 6. Reproduction of a small block of rock showing numerous specimens. Locality 2i, Middle Cambrian sand- 
 stones of Division lb3 of Matthew [1895a, p. 108], on Hanford Brook, St. John County, New Brunswick. 
 U. S. Nat. Mus. Cat. No. 52213f. 
 
PLATE LXXXV. 
 
 283 
 
PLATE LXXXV. 
 
 a. Cardinal area. 
 
 a'. Anterior a<lduclor impressions. 
 
 b. Dental sockets. 
 
 c. Crura. 
 
 d. Deltidium. 
 
 d'. Cast of umbonal cavity. 
 
 j. Cardinal process, 
 
 0. Ovarian spaces. 
 
 r. Visceral area. 
 
 t. Teeth, 
 vs. Vascular sinus. 
 
 BiLLINGSELLA COLORADOENSIS (SllUlUard) (p. 751). 
 
 [Text figs. 5, p. 299, and CO, p. 751.] 
 
 Figure 1. Exterior of typical form of ventral valve, from Locality 70, Upper Cambrian limestone on Morgans Creek, 
 Burnet County, Texas. U. S. Nat. Mus. Cat. No. 34777b. The surface of this specimen is enlarged 
 in figure Ik. It is not the type specimen. 
 
 la. Exterior of a silicified ventral valve, from Locality 302g, Upper Cambrian limestone, north slope of Crow- 
 foot Ridge, Yellowstone National Park, Wyoming. U. S. Nat. Mus. Cat. No. 35213a. Copied from 
 Walcott [1899, PI. LXI, fig. 1]. 
 
 lb. Ventral valve, from Locality 5a, Upper Cambrian limestone of the St. Charles formation, 2 miles southeast 
 of Malade, Oneida County, Idaho. The radiating striae and concentric ridges of growth are very 
 strongly marked on this specimen. Other specimens show the surface characters of figures 1 and le. 
 U. S. Nat. Mus. Cat. No. 51403a. 
 
 Ic. Partly exfoliated ventral valve from Locality 68, Upper Cambrian limestone, Packsaddle Mountain, 
 Llano County, Texas. U. S. Nat. Mus.' Cat. No. 34774a. 
 
 Id. Ventral valve from Locality 97, Upper Cambrian "St. Croix .sandstone, " Reads Landing, Wabasha County, 
 Minnesota. U. S. Nat. Mus. Cat. No. 34771a. 
 
 le. Dorsal valve associated with the specimen represented by figure 1. U. S. Nat. Mus. Cat. No. 34777c. 
 
 If. Dorsal valve associated with specimen represented by figure 1. U. S. Nat. Mus. Cat. No. 34777d. 
 
 Ig. Dorsal valve associated with specimen represented by figure la. L^. S. Nat. Mus. Cat. No. 35213b. Copied 
 from Walcott [1899, PI. LXI, fig. la]. 
 
 Ih. Dorsal valve associated with the ventral valve represented by figure Id. U. S. Nat. Mus. Cat. No. 34771b. 
 
 li. Dorsal valve with strongly marked radiating cost®, associated with the specimen represented by figure Ic. 
 U. S. Nat. Mus. Cat. No. 34774b. 
 
 Ij. Small dorsal valve showing deep mesial sinus. Locality 131, Upper Cambrian "St. Croix sandstone," 4 
 miles east of Lake City, Wabasha County, Minnesota. U. S. Nat. Mus. Cat. No. 34770a. 
 
 Ik. Enlargement of the surface of the specimen represented by figure 1. 
 
 1 1. Group of silicified shells associated with the specimen represented by figure la. U.S. Nat. Mus. Cat. 
 No. 35213c. 
 
 Im. Interior cast of ventral valve, showing marked vascular .sinuses, and a ridge corresponding to a median 
 groove. Same locality as specimen represented by figure Id. V. S. Nat. Mus. Cat. No. .34771c. 
 
 In. Impression of interior of ventral valve probably associa»ted with the specimen represented by figure Id. 
 U. S. Nat. Mus. Cat. No. 34771e. Drawn from an artificial cast, the original mold of which can not 
 be located. The cast, with another (Cat. No. 34771f) which was used to restore portions of figure In, 
 was in a tray with specimens from Locality 97, but it may not belong there. (See fig. lu.) 
 
 lo. Interior of ventral valve associated with the specimen represented by figure la. U. S. Nat. Mus. Cat. No. 
 35213d. Copied from Walcott [1899, PI. LXI, fig. Ic]. 
 
 Ip, Iq, and Ir. Casts of interiors of ventral valves from Locality 83% I'pper Cambrian greensand horizon in 
 "St. CroLx sandstone," Trempealeau, Trempealeau County, Wiscon.sin. These three figures repre- 
 sent unusually convex specimens that may belong to a distinct species. U. S. Nat. Mus. Cat. Nos. 
 52235a, 52235b, and 52235c, respectively. 
 
 Is. Cast of the posterior portion of a ventral valve, with side outline. Locality 70a, Upper Cambrian lime- 
 stone, Morgans Creek, Burnet County, Texas. U.S. Nat. Mus. Cat. No. 34777e. 
 
 It. Cast of the interior of a ventral valve, associated with specimen represented by figure la. U. S. Nat. Mus. 
 Cat. No. 35213e. Copied with slight alterations from the figure given by Walcott [1899, PI. LXI, 
 fig. Id]. 
 284 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LXXXV 
 
 FRANCES W1ESER DEL. 
 
 MELIOTVPC CO BOSTON 
 
PLATE LXXXV. , 285 
 
 BiLLiNGSELLA coLORADOENSis (Sliumard) — Continued. 
 
 Figure lu. Interior of dorsal valve from impression taken from natural cast, with outline of posterior view. Trobably 
 from Locality 97, Upper Cambrian "St. Croix sandstone," Reads Landing, Wabasha County, Minne- 
 sota. U. S. Nat. Mus. Cat. No. 34771g. Drawn from an artificial cast, the original mold of which can 
 not be located. The cast was in a tray with specimens from Locality 97, but it may not belong 
 there. (See note under figure In.) 
 
 Iv. Interior of dorsal valve associated with the specimen represented by figure Ic. U.S.Nat Mus Cat No 
 
 34774c. 
 Iw. Interior of dorsal valve associated with the specimen represented by figure la. U. S. Nat. Mus. Cat. No. 
 
 35213f. Copied with slight alterations from the figure given by Walcott [1899, PI, LXI, fig. lb]. 
 Ix. Cast of the interior of dorsal valve, with side and posterior outlines. U. S. Nat. Mus. Cat. No. 51403b. 
 
 From Locality 5a. (See fig. lb.) 
 ly. Cast of dorsal valve associated with the specimen represented by figure Id. U. S Nat Mus Cat No 
 
 34771d. 
 Iz. Cast of posterior portion of interior of dorsal valve from Locality 5b, Middle Cambrian Langston limestone, 
 
 2 miles (3.2 km.) southeast of Malade, Oneida County, Idaho. U. S. Nat. Mus. Cat. No. 34776a. 
 
PLATE LXXXVI. 
 
 287 
 
PLATE LXXXVI. 
 
 a. Cardinal area. d". Umbonal cavity. 
 
 b. Dental sockets. j. Cardinal process. 
 
 c. Crura. o. Ovarian areas, 
 d'. Cast of umbonal cavity. vs. Vascular sinus. 
 
 BiLLINGSELLA MAJOR Walcott (p. 758). 
 
 Figure 1. Portion of ventral valve, showing cast of cardinal area and surface costse. Locality 116, Upper Cambrian 
 sandstone on Wells farm, 2 miles (3.2 km.) west of Baraboo, Sauk Cotmty, Wisconsin. U. S. Nat. 
 Mus. Cat. No. 52256a. 
 la. Cast of compressed dorsal valve, the type specimen, associated with the specimen represented by figure 1. 
 U. S. Nat. Mus. Cat. No. 52256b. 
 
 Figures 1 and la are copied from Walcott [1908d, PI. X, figs. 1 and la]. 
 
 BiLLINGSELLA ORIENT ALIS (Whitfield) (p. 759). 
 
 Figure 2. Type specimen, compressed in shale. Locality 319g, Lower Cambrian shales in Parker's quarry, near 
 
 Georgia, Franklin County, Vermont. Copied from Whitfield [1884, PI. XIV, fig. 6] where it is 
 
 figured as Orthisina orientalu. 
 
 2a and 2b. Ventral and dorsal valves, from Locality 25a, Lower Cambrian limestone 2 miles (3.2 km.) east of 
 
 Swanton, Franklin County, Vermont. U. S. Nat. Mus. Cat. Nos. 52262a and 52262b, respectively. 
 
 BiLLINGSELLA PLICATELLA Walcott (p. 759). 
 [Text Hg. 1, p. 299.) 
 
 Figure 3. Exterior and side \-iews of a ventral \alvc with rather strongly marked fasciculate costse. U. S. Nat. 
 
 Mus. Cat. No. 52263a. 
 3a. Exterior and side \-iew3 of ventral valve with strong costse. U. S. Nat. Mus. Cat. No. 52263b. 
 3b. Exterior view of ventral valve on which the surface has been partly smoothed by attrition. U. S. 
 
 Nat. Mus. Cat. No. 52263c. 
 3c. Exterior and side views of a very convex ventral valve, marked by very fine radiating striae and faint 
 
 costa. U. S. Nat. Mus. Cat. No. 52263d. 
 3d. Exterior of a small, strongly costate ventral valve from Locality 161, Upper Cambrian limestone in pixnt 
 
 overlooking Churn Canyon, west side of the Bridger Range, Gallatin Coimty, Montana. U. S. Nat. 
 
 Mus. Cat. No. 52265a. 
 3e. Exterior of a small, strongly costate dorsal valve. U. S. Nat. Mus. Cat. No. 52263e. 
 3f. Exterior of ventral valve, partly smoothed by attrition. U. S. Nat. Mus. Cat. No. 52263f. 
 3g. Partly exfoliated ventral valve. U. S. Nat. Mus. Cat. No. 52263g. 
 
 3h. Exterior and side view of dorsal valve smoothed by attrition. U. S. Nat. Mus. Cat. No. 52263h. 
 3i. Cast of interior of ventral valve, the type specimen, showing cardinal area, a; cast of va.scuhir sinus, vs; 
 
 and ovarian areas, o. U. S. Nat. Mus. Cat. No. 522631. 
 3j. Cast of interior and side outline of a transverse ventral valve. U. S. Nat. Mus. Cat. No. 52263J. 
 3k. Cast of interior and side outline of ventral valve, on which the vascular and other impressions are strongly 
 
 marked. U. S. Nat. Mus. Cat. No. .52263k. 
 3 1. Cast of the interior of dorsal valve. U. S. Na(. Mus. Cat. No. 52263 1. 
 3m and 3u. Interiors of small, strongly marked ventral and dorsal valves from Locality 4j, Middle Cambrian 
 
 limestones at the head of Deep Creek, Canyon ([uadrangle (l^ S. Geol. Survey), Yellowstone National 
 
 Park, Wyoming. U. S. Nat. Mus. Cat. Nos. 52266a and 52266b, respectively. 
 
 With the exception of figures 3d, 3m, and 3n, all of the specimens represented are from Locality 158, Upper 
 Cambrian limestone north of East Gallatin River, near Hillsdale, Threeforks quadrangle (U. S. Geol. Survey), 
 Gallatin County, Montana. 
 288 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LXXXVl 
 
 •« i i "-.Vi'i 
 
 '-itm 
 
 /^'i 
 
 ■.^^ 
 
 / 
 
 "^ '^ 
 
 PRANCES WIE3ER DEL. 
 
 MCLIOTVPE CO BOSTON 
 
PLATE LXXXVI. 289 
 
 BiLLINGSELLA STRIATA Walcott (p. 764). 
 
 Figure 4. Exterior of ventral valve, the type specimen. U. S. Nat. Mu.s. Cat. No. 52279a. 
 4a. Partly exfoliated ventral valve. U. S. Nat. Mus. Cat. No. 52279b. 
 4b. Cast of interior of ventral valve and side outline. U. S. Nat. Mus. Cat. No. 52279c. 
 4c. Cast of imperfect dorsal valve. U. S. Nat. Mus. Cat. No. 52279d. 
 
 The specimens represented are all from Locality 149a, Middle Cambrian limestone at the forks of Polo Creek, 
 above Cherry Creek Basin, Threeforks quadrangle (U. S. Geol. Survey), Madison County, Montana. 
 
 BiLLINGSELLA WHITFIELDI (Walcott) (p. 764). 
 
 Figure 5. Exterior of ventral valve, with outline restored, from Locality 65, Middle Cambrian Eldorado limestone 
 [Walcott, 1908f, p. 184], east slope of Prospect Mountain, in New York Canyon, Eureka district, 
 Nevada. U. S. Nat. Mus. Cat. No. 24591a. 
 5a. Exterior of dorsal valve from Locality 55b, Middle Cambrian Eldorado limestone, west side of Secret 
 Canyon, Eureka district, Nevada. V. S. Nat. Mus. Cat. No. 57041a. This is the type specimen. 
 
 The figures (5 and 5a) are redrawn from the specimens illustrated by Walcott [1884b, PI. IX, figs. 4, 4a-b]. 
 
 BiLLINGSELLA OBSCURA Walcott (]). 758). 
 
 Figure 6. Exterior of an imperfect dorsal valve from Locality 74, Middle Cambrian .sandstone about .300 feet (91.4 m. 
 above the base of the Tonto group at the head of Nunkoweap Valley, Grand Canyon of the Colo- 
 rado, Arizona. U. S. Nat. Mus. Cat. No. 52258a. This is the type specimen. 
 
 62667°— VOL 52, pt 2—12 19 
 
PLATE LXXXVII. 
 
 291 
 
PLATE LXXXVII. 
 
 WiMANELLA? ANOMAI.A (Walc.ott) (p. 745). 
 
 Figure 1. Exterior of a compressed ventral valve, the type specimen. U. S. Nat. Mw.'^. Cat. No. 55223a. 
 la. Impression in shale of imperfect, compressed ventral valve. U. S. Nat. Mus. Cat. No. 55223b. 
 lb. Area and posterior portion of imperfect, compressed ventral valve. V. S. Nat. Mus. Cat. No. 55223c. 
 Ic. Interior of distorted dorsal valve. U. S. Nat. Mus. Cat. No. 55223d. 
 Id. Impression in shale of distorted dorsal valve. V. S. Nat. Mus. Cat. No. 55223e. 
 le. Exterior of dorsal valve doubtfully referred to this species. U. S. Nat. Mus. Cat. No. 55223f. 
 
 The specimens represented are all from Locality 90, Middle Cambrian Conasauga shale on Edwards farm, near 
 Craigs Mountain, about 10 miles (Ki km.) southeast of Center, Cherokee County, Alabama. 
 
 BiLLINGSELLA ? APPALACHIA Walcott (p. 750). 
 
 Figure 2. Compressed and distorted ventral valve. U. S. Nat. Mus. Cat. No. 57073a. 
 
 2a. Compressed ventral valve, the type specimen, preser\-ing surface costae. U.S. Nat. Mus. Cat. No. 57073b. 
 2b. Impression in shale of compressed dorsal valve. U. S. Nat. Mus. Cat. No. 57073c. 
 
 The specimens represented are all from Locality 121, Middle Cambrian Rogers^^lle shale, road just east of Harlan 
 Knob, 4 miles (6.4 km.) northeast of Rogersville, Hawkins County, Tennessee. 
 
 BiLLINGSELLA SALEMENSIS (Walcott) (p. 763). 
 
 FiGUUE 3. Exterior view of the type specimen, a \entral valve, with side outline. The slope of the cardinal area is 
 drawn in from the position of the beak and the cardinal angle. U. S. Nat. Mus. Cat. No. 17443a. 
 3a. Exterior of an imperfect dorsal valve. U. S. Nat. Mus. Cat. No. 17443b. 
 
 The specimens represented by figures 3 and 3a are from Locality 36, Lower Cambrian limestone, 1 mile (1 .6 km.) 
 south of Shushan and 3.5 miles (5.6 km.) north-northeast of Cambridge, \\ashington County, New York. The figures 
 (3 and 3a) are redrawn from the specimens illustrated by Walcott [1887, PI. I, figs. 17 and 17a, respectively]. 
 
 BiLLINGSELLA HIGHLANDENSIS (VV'^alcott) (p. 756). 
 
 Figure 4. Exterior of imperfect ventral valve. U. S. Nat. Mus. Cat. No. 15355a. Specimen figured by Walcott 
 [188eb, PI. VIII, fig. 3b]. 
 4a. Interior cast of ventral valve, the outline of which has been restored from another specimen (Cat. No. 
 
 1535oe). U. S. Nat. Mus. Cat. No. 1535.5b. 
 4b. Interior cast of a ventral valve with deep furrows that represent the ridges of the main vascular trunks 
 and the median ridge at the bottom of the delthyrium. The cast of the dental plates is also clearly 
 shown. U. S. Nat. Mus. Cat. No. 15355c. Type specimen figured by Walcott [ISSGb, PI. VIll, fig. 3a]. 
 4c. Imperfect cast of the interior of a dorsal valve. IT. S. Nat. Mus. Cat. No. 15355d. Specimen figured by 
 Walcott [1886b, PI. VIII, fig. 3]. 
 The specimens represented are all from Locality 31a, Lower Cambrian limestone in Pioche formation near Pioche, 
 Lincoln County, Nevada. 
 
 WiMANELLA HAULAXENSIS (Walcott) (p. 746). 
 
 Figure 5. Exterior of imperfect ventral valve. U. S. Nat. Mus. Cat. No. 52252a. Another specimen (Cat. No. 
 
 52252b) was used in drawing certain portions of this figure. 
 5a. Exterior of dorsal valve. U. S. Nat. Mus. Cat. No. 52252c. 
 5b. Cast of interior of ventral valve, the type specimen, associated on same hand specimen with figure 5a. 
 
 U. S. Nat. Mus. Cat. No. 52252d. 
 5c. Partial cast of interior ot ventral valve. V. S. Nat, Mus. Cat. No. 52252e. 
 5d. Caat of interior of a beautifully preserved portion of an abnormal dorsal valve. U. S. Nat. Mus. Cat. 
 
 No. 52252f. Another specimen (Cat. No. 522.52g) was used in drawing certain portions of this figure. 
 
 The specimens represented are all from Locality 121, Middle Cambrian Rogersville shale, road just east of Harlan 
 Knob, 4 miles (G.4 km.) northeast of Rogersville, Hawkins County, Tennessee. 
 292 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LXXXVH 
 
 FRANCES WIESER DEL. 
 
 MELIOTypE CO BOSTON 
 
PLATE LXXXVII. 293 
 
 BiLLiNGSKLLA LiNDSTROMi (Linnarsson) (p. 757). 
 
 Figure 6. Exterior and side views of nearly entire ventral valve from Locality 320n, Middle ("ambrian limestones of 
 the Paradojcides forchhammeri zone at Lovened, Djupadal, 19 miles (30.6 km.) south-southeast of 
 Skara, Province of Skaraborf;, Sweden. U. S. Nat. Mus. Cat. No. 52260a. 
 
 6a and 6b. Exterior views of ventral and dorsal valves with coarse costEe. U. S. Nat. Mus. Cat. Nob. 52259a 
 and .522.59b, respectively. 
 
 6c and 6d. Exterior and side views of dorsal valves. U. S. Nat. Mus. Cat. Nos. 522.59c and 52259d, respec- 
 tively. 
 
 6e. Cast of the interior of a ventral valve. U. S. Nat. Mus. Cat. No. 52259e. 
 
 6f. Cast of the interior of a dor,sal valve. U. S. Nat. Mus. Cat. No. .522.59f. The beak is added from another 
 specimen (Cat. No. 52259g). 
 
 The specimens represented by figures 6a-f are all from Locality 320q, Middle Cambrian limestones of the 
 Paradoxides forchhamtneri zone at Alunbruk (alum works), southern part of Oelaiid I.sland, Sweden. 
 
 WiMANELLA SAFFORDI (Walcott) (p. 747). 
 
 Figure 7. Cast of interior of a ventral valve, the type specimen. U. S. Nat. Mus. Cat. No. 52268a. 
 7a. Cast of interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52268b. 
 The specimens represented are both from Locality 14a, Middle Cambrian sandstone of the Rome formation along 
 First Creek Gap, 4 miles (6.4 km.) north-northeast of Knoxville [Keith 1905, areal geology sheet], Knox County, 
 Tennessee. 
 
PLATE LXXXVIII. 
 
 295 
 
PLATE LXXXVIII. 
 
 a'. Anterior adductor impressions. <i'. Cast of umbonal cavify. 
 a". Posterior adductor impressions. j. Cardinal process. 
 
 c. Crura. s. Median septum, 
 
 cp. Septal plates. 
 
 BiLLiNGSELL.\ EXPORRECTA (Liiuiarsson ) (p. 754). 
 
 Figure 1. Exterior and side views of a ventral valve preserving the outer .surface. U. S. Nat. Mus. Cat. Xo. 52249a. 
 la. Exterior and side views of ventral valve, in which the plications are stronger than in the specimen repre- 
 sented by figure 1. U. S. Nat. Mus. Cat. No. 52249b. 
 lb. Dorsal valve flattened in the shale. U. S. Nat. Mus. Cat. No. 52249c. 
 
 Ic. Exterior and side views of rather strongly costate dorsal valve. U. S. Nat. Mus. Cat. No. 52249d. 
 Id and Id'. Top, side, and back views of a cast of a somewhat quadrate ventral valve. U. S. Nat. Mus. Cat. 
 
 No. 52249e. 
 le. Top and side views of the ca.st of a transverse ventral valve. U. S. Nat. Mus. Cat. No. 52249f. Another 
 
 specimen (('at. No. 52249g) was used to restore certain portions of this figure. 
 If. Interior of a dorsal valve, with strongly developed median ridge. U. S. Nat. Mus. Cat. No. 52249h. 
 Ig. Cast of the interior of a dorsal valve, having very strongly marked muscle scars. U. S. Nat. Mus. Cat. No. 
 
 522491. 
 Ih. Interior of a dorsal valve with strongly marked muscle scars. U. S. Nat. Mus. Cat. No. 52249J. The 
 
 specimen represented occurs on the same hand specimen with that represented by figure 1 1. 
 li. Interior of a dorsal valve that should be compared with the interior represented by figure If. U. S. Nat. 
 
 Mus. Cat. No. 52249k. 
 Ij. Cast of the interior of a dorsal valve, with very strong muscle scars. U. S. Nat. Mus. Cat. No. 52249 1. 
 Ik. Cast of the interior of a dorsal valve, with strong muscle scars and vascular sinuses. U. S. Nat. Mus. Cat. 
 
 No. 52249m. 
 1 1. Cast of the interior of dorsal valve, with rather faintly marked muscle scars. U. S. Nat. Mus. Cat. Xo. 
 
 52249n. This specimen is associated on the same hand specimen with the specimen represented by 
 
 figure Ih. 
 
 The specimens represented are all from Locality 320b, Middle Cambrian limestones of ihe Agnostus Isevigatus zone 
 at Gudhem, 12.5 miles (20.1 km. ) south-southeast of Skara, Province of Skaraborg, Sweden. 
 
 BiLLINGSELLA EXPORRECTA RUGOSICOSTATA Walcott (p. 755). 
 
 Figure 2. Top and side views of a cast of the interior of a \-entral valve, the type specimen, having very strongly 
 marked costse. U. S. Nat. Mus. Cat. No. 52250a. 
 
 2a. Top and side ^■iews of a cast of the interior of a ventral valve, having strongly marked costas with fine radi- 
 ating strise upon them. f. S. Nat. Mus. Cat. No. 522.50b. 
 
 2b. Top and side views of a cast of the interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52250c. 
 
 2c. Top and side views of a cast of the interior of a dorsal valve less strongly costate than most specimens of 
 this variety. U. S. Nat. Mus. Cat. No. 52250d. 
 
 The specimens represented are all from Locality 320b, Middle (^ambrian limestones of the Agnostus Ixiigatus 
 zone at Gudhem, 12.5 mUes (20.1 km.) south-southeast of Skara, Province of Skaraborg, Sweden. 
 296 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH Lt PL. lXxxv II 
 
 ^SF^ 
 
 if 'mm 
 
 K 
 
 
 / 
 
 
 
 PRANCES WIESER DEL. 
 
 -lOTYPE CO eOSTOM 
 
PLATE LXXXIX. 
 
 297 
 
PLATE LXXXIX. 
 
 ct. Cardinal muscle scar. j. Anterior lateral muscle scar, 
 
 d. Dcllhyriuin. vs. Vascular sinus, 
 
 h. Central muscle scar. 
 
 BiLLINGSELLA RICHTHOFENI Walcott (p. 761). 
 
 Figure 1. Exterior of ventral valve, the type specimen, with .^ide outline, from Locality C3, Lower Cambrian Manto 
 shale, 2.5 miles (4 km.) southwesit of Yenchuang, Sintai district, Shantung, China. U. S. Nat. 
 Mus. Cat. No. 52559a. 
 
 WiMANELLA SIMPLEX Walcott (p. 748). 
 [Text fig. 04, p. 748.] 
 
 Figure 2. Ventral valve from Locality 4v, Lower Cambrian shale on Gordon Creek, 6 miles (9.6 km.) from the South 
 
 Fork of the Flathead River, Ovando quadrangle (U. S. Cieol. Survey), Powell County. Montana. 
 
 U. S. Nat. Mus. Cat. No. 52278a. Copied from Walcott [190Sd. PL N. fig. 2]. This is the type 
 
 specimen. 
 2a, 2b, and 2c. Ventral valves of varying outlines owing to distortion in the shales of Locality 4w, Lower 
 
 Caml)rian shales on Youngs Creek, about 5 miles (8 km.) from its junction with Danaher Creek, 
 
 Ovando quadrangle (U. S. Geol. Survey), Powell County, Montana. U. S. Nat. Mus. Cat. Nos. 
 
 52277a-c, respectively. 
 2d. Cast of interior of ventral valve associated with the sjiecimens represented by figures 2a-c. V. S. Nat. 
 
 Mus. Cat. No. 52277d. 
 2e. Ventral and dorsal valves compressed and resting against each other at the posterior margins, associated 
 
 with the specimen represented by figure 2. V. S. Nat. Mus. Cat. No. 5227Sb. 
 
 Otusia utahensis "Walcott (p. 770). 
 
 Figure 3. Transverse dorsal valve, the type specimen, l'. S. Nat. Mus. Cat. No. 522Sla. 
 3a. Ventral valve with rounded cardinal angles. U. S. Nat. Mus. Cat. No. 522Slb. 
 3b. Fragment of a dorsal valve. U. S. Nat. Mus. Cat. No. 52281c. 
 3c. Enlargement of outpr surface. U. S. Nat. Mus. Cat. No. 52281d. 
 
 The specimens represented are from Locality 33r, Middle Cambrian limestone in canyon about 1 mile (1.6 km.) 
 east of Cricket Spring. Cricket Range (locally known as the Beaver River Range or the Beaver Mountains^ northwest 
 of Black Rock. Millard County. Utah. 
 
 Wyxnia warthi (Waagen) (p. 771). 
 
 [Text figs. (;s.\ and OSA', p. 771.) 
 
 Figure 4. Cast of the interior of the ventral valve represented Ijy figure 4b. showing faint muscle area and strong 
 vascular sinuses. This figure is incorrect and is superseded by text figure 68A, page 771, which see. 
 Geol. Survey India Cat. No. 4 124. The area of this specimen was figured by Waagen [1891, PI. 
 II, fig. 14]. " 
 
 4a. Cast of the interior of another ventral ^•alve showing faint muscle area and strong vascular sinus. Geol. 
 Survey India Cat. No. 4/122. Type specimen figured liy Waagen [1891, PI. I. figs. 12a-b]. 
 
 4b. Area of the specimen represented Ijy figure 4. The small deltidium represented in the drawing is a mis- 
 take; there is none on the specimen. The delthjTium is much too large in the drawing owing to the 
 breaking away of the point of the beak. The specimen is correctly represented in text figure 68A', 
 page 771, which see. Geol. Survey India Cat. No. 4 124. Specimen figured in this position by 
 W.iagcn [1891, PI. II, fig. 14]. 
 
 4c. Cast of the interior of a doi-sal valve. This valve is fitted in its proper place to the ventral valve repre- 
 sented liy figure 4a, and the two valves probably belong to tlie same specimen. Geol. .Survey India 
 Cat. No. 4/122. 
 
 4d, 4e, and 4f. Diagrammatic figures of a very young individual showing the two valves united. Copied 
 from Waagen [1891. PI. II, figs. 2a-c]. 
 
 The specimens represented are all from Locality 357d, Middle Cambrian concretionary shales of the Kliussak 
 group at several localities between Chel Hill and Kiura (Khewrai. eastern part of the .Salt Range. India. The speci- 
 mens represented by figures 4 and 4a likely occur in the ^•icinity of Ch^l Ilill. Tliey are all in the collection of the 
 Geological Survey of India. 
 298 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. LXXXIX 
 
 [...:.■■ 
 
 3, 
 
 \ 
 
 ^ 
 
 FRANCES WIESER DEL. 
 
 MELIOT/PE ^C SaSTON 
 
PLATE LXXXIX. 299 
 
 EooRTHis KicHOUENsis (Walcott) (j). 782). 
 
 Figures 5 and 5'. Exterior and side views of a ventral valve, the type specimen, from Locality C78, Middle Cambrian 
 limestone, Kichou formation, 4.5 miles (7.2 km.) south of Wutaihien, Shaiisi, China. U. S. Nat. Mus. 
 Cat. No. 52550a. 
 
 EooRTHis AGRESTE (Walcott) (p. 773). 
 
 Figure 6. Exterior and side views of a ventral valve, the type specimen, from Locality C28, Middle Cambrian 
 Changhia limestone 1 mile (1.6 km.) east-southeast of Changhia. .Shantung, China. U. S. Nat. Mus. 
 Cat. No. 52545a. 
 Ga. Enlargement of the radiating rilis on another specimen. U. S. Nat. Mus. Cat. No. 52545b. 
 
 EooRTHis sp. undt. c (Walcott) (p. 793). 
 
 Figure 7. Exterior and side views of a small ventral valve from Locality C26, Middle Canil)rian Changhia limestone 
 2 miles i3.2 km.) north-northeast of Changhia, Shantung, China. IT. S. Nat. Mus. Cat. No. 52554a. 
 
 EooRTHis sp. midt. d (Walcott) (p. 793). 
 
 Figure 8. Exterior of a ventral valve from Locality C71, Middle Cambrian limestone, Kichou formation, 4 mileS 
 (C.4 km.) southwest of Tungyn, Shansi, China. V. S. Nat. Mus. Cat. No. 52555a 
 
 HUENELLA ETHERIBGEI Walcott (p. S07). 
 
 Figures 9 and 9'. Top and side views of a dorsal valve from Locality 315c. Middle ? Cambrian. Archseocyathinfe white 
 limestone at "Wirrialpa, Flinders Range, South Australia. Type specimen in the collection of the 
 LTniversity of Adelaide, South Australia; cast in the United States National Museum, Cat. No. 53G78b. 
 9a and 9a'. Top and side views of a ventral valve associated with the specimen represented by figure 9. 
 Original in the collection of the University of Adelaide, South Australia; cast in the LTnited States 
 National Museum, Cat. No. 53678a. 
 
 The figures are both copied from Walcott [1908d, PL X, figs. 13a and 13, respectively]. They represent the 
 specimens illustrated by Etheridge [1905, PI. XXV, figs. 10 and 9, respectively] as Orthis (or Orthlsina) sp. 
 
 DiCELLOMUS PROLiFicus Walcott (p. 57S). 
 
 FiGURE.s 10 and 10'. Top view and side outline of a broad form of the ventral val\-e, the type specimen. IT. S. Nat. 
 Mus. Cat. No. 51925a. Copied from Walcott [1908d, PI. VIII, fig. 3]. 
 10a and 10a'. Top view and side outline of a narrow ventral valve. U. S. Nat. Mus. Cat. No. 51925c. 
 10b and 10b'. Top view and side outline of dorsal valve. U. S. Nat. Mus. Cat. No. 51925b. Copied from 
 Walcott [1908d. PI. VIII, fig. 3a]. 
 
 The specimens represented are all from Locality lOz, Middle Cambrian Marjum limestone in the long cliff about 
 2 miles (3.2 km.) southeast of Marjum Pass [Walcott, 19081. p. 179 and Pis. XIII and XV], House Range. Utah. 
 
 DiCELLOMUS PARVUS Walcott (p. 574). 
 
 Figure 11. Top ^^ew of partly exfoliated ventral valve. U. S. Nat. Mus. Cat. No. 52523c. 
 
 11a and lib. Interiors of dcjr.sal valves. U. S. Nat. Mus. Cat. Nos. 52o23a and 52523b, respectively. Copied 
 from Walcott [190Sd. PI. VIII, figs. 2 and 2a, respectively]. Figure lib represents the type specimen, 
 lie. Exterior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52523d. 
 lid. Exterior of a young shell. I^. S. Nat. Mus. Cat. No. 52.D23e. 
 
 The figures represented are all from Locality C6, Middle Cambrian .shales, Kiulung group. 2.5 miles (4 km. ) .south- 
 west of Yenchuang, Sintai district. Shantung. China. 
 
PLATE XC. 
 
 301 
 
PLATE XC. 
 
 a. Cardinal area. d'. Cast of umbonal cavity, 
 a'. Anterior adductor impressions. j. Cardinal process. 
 
 b. Dental sockets. o. Ovarian area:>. 
 
 c. Crura. vs. Vascular sinus. 
 
 BiLLINGSELLA RETROFLEXA (Matthew) (p. 761). 
 
 Figure 1 . Cast of the exterior of a rather coarsely costate ventral valve. University of Toronto, Canada, 
 la. Cast of the exterior of a finely costate ventral valve. University of Toronto, Canada. 
 lb. Cast of the exterior of a small, compressed ventral valve, with a strongly marked mesial depression. 
 
 University of Toronto, Canada. 
 Ic. Matrix of the exterior of a large dorsal valve. University of Toronto, Canada. Specimen figured by 
 
 Matthew [1903, PI. X, fig. 2d]. 
 Id. Cast of the e.xterior and side outline of a dorsal valve. University of Toronto, Canada, 
 le. Enlargement of the costse and radiating striae, as shown in the matrix of the anterior portion of the shell 
 
 University of Toronto, Canada. 
 If. Cast of a partly exfoliated dorsal valve. University of Toronto, Canada. 
 Ig. Cast of the interior of a ventral valve. University of Toronto, Canada. Specimen figured by Matthew 
 
 [1895, PI. II, fig. lb] as Clilambonites (Gonainbonitcs) plana retrojlaa. • 
 
 Ih. Cast of a portion of the interior of a ventral valve, in which portions of the ca.st of the outer surface of the 
 
 shell are preserved. University of Toronto, Canada. Type specimen figured by Matthew [1895, 
 
 PI. II, fig. la] as Clilamboniles (Goiianibonites) plana retrojtexa. 
 
 The specimens represented are all from Locality 307d, Middle Cambrian sandy limestone on Young (McFees) 
 Point, near George Paver, Cape Breton, Nova Scotia. 
 
 BiLLiNGSELL.v KOMiNGERi (BaiTande) (p. 762). 
 
 Figures 2, 2a-d. Ventral, dorsal, side, front, and posterior views of the type specimen in which the two valves are 
 united, from Locality 345f, Middle Cambrian Etage C, near Skrej, Bohemia. Figures 2, 2a-d are copied from 
 Barrande [1879a, Pl.'LXII, figs. II: 3a, 3c, 3b, 3d, and 3e, respectively]. 
 
 Figure 2e. Exterior and side views of a ventral valve. U. S. Nat. Mus. Cat. No. 52267a. 
 
 2f. Matrix of ventral valve in which the area is preserved. U. S. Nat. Mus. Cat. No. 52267b. The specimen 
 is on the same hand fragment with the ventral valve .shown in figure 2h. 
 
 2g, 2h, and 2i. Casts of the interiors and side outlines of ventral valves. L". S.Nat. Mus. Cat. Nos. 52267c, 
 52267d, and 52267e, respectively. The specimen represented by figure 2h is on the same hand frag- 
 ment as the one shown in figure 2f. 
 
 2j. Cast of interior and side view of a dorsal valve. U. S. Nat. Mus. Cat. No. 52267f. 
 
 2k. Cast of the interior and side view of a dorsal valve showing very strong muscular impressions. V. S. Nat. 
 Mus. Cat. No. 52267g. 
 
 2 1. Cast of the interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52267h. 
 
 2m. Cast of the interior of a very small ventral valve. U. S. Nat. Mus. Cat. Xo. 522G7i. 
 
 2n, 2n', and 2n". Top, posterior, and side views of the cast of the interior of a ventral valve in which the 
 vascular trunks are readily traced to the back of the intcrinr (if the b^>ak. U. S. Nat. Mus. Cat. No. 
 522G7J. 
 
 The specimens represented by figures 2e-n are from Locality 345, Middle Cambrian .^hale on the I)h)uha llnra, 
 above the brook of Sbirov, near Skrej, Bohemia. 
 302 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XC 
 
 FRANCES WIESER DEL. 
 
 LiOTv^e CO BOSTON 
 
PLATE XCI. 
 
 303 
 
PLATE XCI. 
 
 b. Dental sockets. d'. Cost ot umbonal cavity. 
 
 c. Crura. i- Cardinal process. 
 
 EooKTHis REMNiCHA (X. H. Wiiichcll) (p. 786). 
 
 [Text ng. 7, p. 299, and PI. XCII, figs. 2, 2a-d, 3, 3a-e.] 
 FiouEES 1, la. and 11). Casts, taken in a natural mold, of ventral valves in which the costa and mesial sinus show 
 
 wide variation in form. U. S. Nat. Mus. Cat. Nos. 52361a, 523011), and 52361c respectively. 
 Ic. Top view, with side and back outlines, of a natural cast of part of the interior of a ventral valve. The 
 
 tripartite divi.sion of the interior of the shell (visceral area) opposite the deltidium is finely shown. 
 
 U. S. Nat. Mus. Cat. No. 62361d. 
 Id. Natural cast ot the interior of a ventral valve, with strong rounded costse. U. S. Nat. Mus. Cat. No. 
 
 52361e. 
 le. Natural cast of the interior of a ventral valve, with fine costse and short auricula te extension of the cardinal 
 
 angles. U. S. Nat. Mus. Cat. No. 52361f. 
 If and Ig. Natural casts of small finely costate ventral valves, with slightly auriculate cardinal angles. U. S. 
 
 Nat. Mus. Cat. Nos. 52361g and 52361h, respectively. 
 Ih. Natural cast of strongly costate ventral valve, with short cardinal line. Locality 80a, Upper Cambrian 
 
 " St. Croix sandstone " 4 miles (6.4 km.) north of Reedsburg, Sauk County, Wisconsin. U. S. Nat. Mus. 
 
 Cat. No. 523G2a. 
 11. Cast in natural mold of a ventral valve, with short cardinal line, strong costse, and median sinus. U. S. 
 
 Nat. Mus. Cat. No. 523611. 
 Ij. Natural cast of a small ventral valve, with very strong costse. U. S. Nat. Mus. Cat. No. 52361J. 
 Ik. Natural cast of a ventral valve, with fine costse interspaced between strong costse. U. S. Nat. Mus. Cat. 
 
 No. 52361k. 
 1 1. Natural cast of a ventral valve, with strong costa? much like those of figure Id. A gradation of the strength 
 
 of the costse is noticeable from figure 1 1 through figiu-es Id, Ij, lb, Ic, Ih, If, and Ig. The specimen 
 
 represented liy figure 11 is associated with the ventral valve shown in figure Ih. U. S. Nat. Mus. 
 
 Cat. No. 52362b. 
 Im, In, lo, Ip, and Irj. Natural casts of dorsal valves, showing variation in form and strength of surface costse. 
 
 U. S. Nat. Mus. Cat. Nos. 52361 1-p, respectively. 
 Ir. Enlargement of the posterior portion of figure Iq. U. S. Nat. Mus. Cat. No. 52361p. 
 Is. Enlargement of the surface of a ventral valve from Locality 12n, Upper Cambrian limestone of the Reagan 
 
 sandstone, sec. 1, T. 2 S.,R. 1 E., Ardmore quadrangle (U. S. Geol. Survey*. Carter County. Okla- 
 homa. U. S. Nat. Mus. Cat. No. 5235Ga. 
 
 \Mth the exception of figures Ih, 1 1, and Is the specimens repre.sented are all from Localit\- 97a, Upper Cambrian 
 "St. Croix sandstone " near Winfield, Jeffer.son County. Wisconsin. 
 
 EOORTHIS REMNICHA WINFIELDENSIS (Walcott) (p. 788). 
 
 Figure 2. Exterior and side views of a cast in a natural mold of the exterior surface of a ventral valve, the type 
 specimen. U. S. Nat. Mus. Cat. No. 52374a. 
 2a, 2b, and 2c. Three natural casts of ventral valves that illustrate variation in form. U. S. Nat. Mus. Cat. 
 
 Nos. 52374b, 52374c, and 52374d, respectively. 
 2d. Exterior and side views of natural cast of exterior of dorsal valve. U. S. Nat. Mus. Cat. No. 52.374e. 
 2e. Exterior, side, and back views of natural cast of a dorsal valve. U. S. Nat. Mus. Cat. No. 52374f. 
 The specimens represented are all from Locality 97a, Upper Caml>riaii ''St. Croix sandstone" near Winfield, 
 Jefferson County, Wisconsin. 
 
 EooRTiiis IDDINGSI (Walcott) (p. 780). 
 
 Figure 3. Ventral valve. The outline is partly restored from another shell. U. S. Nat. Mus. Cat. No. 52340a. 
 
 Type specimen figured by Walcott [1899, PI. LXII, fig. la] as Eoorthis rcmnicha. 
 3a. A small dorsal valve. U. S. Nat. Mus. Cat. No. 52340b. Specimen figured by Walcott [1S99, PI. LXII, 
 
 fig. lb] as Eoorthis remnicha. 
 3b. Interior of a ventral valve. U. S. Nat. Mus. Cat. No. 52340c. 
 
 The specimens represented are all from Locality 302c, L^pper Cambrian shaly limestone on south side of Gallatin 
 Valley, Yellowstone National Park, ^\'yonling. 
 
 Eoorthis papias (Walcott) (p. 78.5). 
 
 Figure 4. Top and side views of the type and oidy specimen of the species in the collection. Locality 61, Middle 
 Cambrian shales near the top of No. 6 of the Manuels Brook .section [Walcott. 1891b. p. 261]. east side 
 of Manuels Brook, Conception Bay. Newfoundland. U. S. Nat. Mus. Cat. No. 52353a. 
 304 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XCl 
 
 FRANCES WIESER DEL. 
 
 MELIOTYPG CO SOSTOtt 
 
PLATE XCII. 
 
 62667°— VOL 51, pt 2—12 20 305 
 
PLATE XCII. 
 
 1). Dental sockets. d'. Umbonal cavity, 
 
 c. Crura. j. Cardinal process. 
 
 EOORTHIS REMNICHA SULCATA (Walcott) (p. 787). 
 
 Figures 1 and lb. Natural cast of dorsal valves from Locality 97a, Upper Cambrian sandstone near Winfield, Jefferson 
 County, Wisconsin. U. S. Nat. Mus. Cat. Nos. 52365a and 52365b, respectively, 
 la and Ic. Natural casts of dorsal valves from Locality 80a, Middle Cambrian sandstone 4 miles (6.4 km.) 
 north of Reedsburg, Sauk County, Wi-sconsin. U. S. Nat. Mus. Cat. Nos. 52366a and .52366b, respec- 
 tively. Figure la represents the type specimen. 
 
 EooRTHis REMNICHA (N. H. Wincliell) (p. 786). 
 
 [Text fig. 7, p. 299, and PI. XCI, figs. 1, la-s.) 
 
 Figure 2. E.xterior of dorsal valve from Locality 302b, Middle Cambrian limestones near Crowfoot Ridgo, Yellowstone 
 
 National Park, Wyoming. U. S. Nat. Mus. Cat. No. 35215a. Specimen figured by Walcott [1899, 
 
 PI. LXII, fig. 1]. 
 2a. Interior of ventral valve from Locality 302n, Upper Cambrian limestone on south side of Gallatin Valley, 
 
 Gallatin County, Montana. U. S. Nat. Mus. Cat. No. 52354a. Specimen figured by Walcott [1899, 
 
 PI. LXI, fig. 3a]. 
 2b. Interior of dor.sal valve associated with the specimen represented by figure 2a. U. S. Nat. Mus. Cat. 
 
 No. 52354b. Specimen figured by Walcott [1899, PI. LXI, fig. 3]. 
 2c. Enlargement of exterior of a ventral valve associated with the specimen represented by figure 2, showing 
 
 fine radiating striae. U. S. Nat. Mus. Cat. No. 35215b. Specimen figured by Walcott [1899, PI. 
 
 LXII, fig. Id]. 
 2d. Ventral and dorsal valves associated with the specimen represented by figure 2a, showing fine radiating 
 
 stria. U. S. Nat. Mus. Cat. No. 52354c. Specimen figured by Walcott [1899, PI. LXII, fig. Ic]. 
 3; 3a, 3a', 3a"; and. 3c. Threeventral valves illustrating variation in form and costae. The fine radiating striae 
 
 so characteristic of the specimens represented by figures 2c and 2d are largely exfoliated with the 
 
 matrix. A few traces of the striae are shown by figure 3a. Locality 12k, Upper Cambrian limestone 
 
 of the Reagan sandstone, sec. 35, T. 1 S., R. 1 E., Ardmore quadrangle. Carter County, Oklahoma. 
 
 U. S. Nat. Mus. Cat. Nos. 52355a, 52355b, and 52355c, respectively. 
 3b. Ventral valve from Locality 12n, Upper Cambrian limestone of the Reagan sandstone, sec. 1, T. 2 S., 
 
 R. 1 E., Ardmore quadrangle. Carter County, Oklahoma. U. S. Nat. Mus. Cat. No. 52356h. 
 3d. Broad form of dorsal valve associated with the specimen represented by figure 3b. L^. S. Nat. Mus. Cat. 
 
 No. 52356c. 
 3e. Elongate form of dorsal valve associated with the specimen represented by figure 3. U. S. Nat. Mus. 
 
 Cat. No. 52355d. 
 
 EOORTHIS REMNICHA TEXANA (Walcott) (p. 787). 
 
 Figures 4, 4'; 4a; and 4b. Three ventral valves, varying in form and surface characters, from Locality 71, Upper 
 Cambrian limestone in Cold Creek Canyon, Burnet County, Texas. U. S. Nat. Mus. Cat. Nos. 52369a, 
 52369b, and 52369c, respectively. Figure 4 represents the type specimen. 
 
 4". Back \-iew of a large ventral valve associated with the specimen represented by figure 4c. The specimen 
 can not be located. U. S. Nat. Mus. Cat. No. 52370b. 
 
 4c. Dorsal valve from Locality 12m, Upper Cambrian Arbuckle limestone, sec. 2, T. 2 S., R. 1 E., .Vrdmore 
 quadrangle, Carter County, Oklahoma. U. S. Nat. Mus. Cat. No. 52370a. 
 
 4d, 4e, 4f, and 4g. Dorsal valves, varying in form and surface characters, ass.iciated with the specimens 
 represented by figures 4, 4a-b. U. S. Nat. Mus. Cat. No.^. 52369d-g, respectively. 
 
 306 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XCII 
 
 FRANCES WIESER OEL. 
 
 HCt.lOTVP6 CO BOSTON 
 
PLATE XCIII. 
 
 307 
 
PLATE XCIII. 
 
 a. Cardinal area. 
 
 a'. Anterior udductor impressions, 
 a". Posterior adductor impressions. 
 
 b. Dental soeket.s. 
 d. Delthyrium. 
 
 d'. Cast of umbonal cavity. 
 
 j. Cardinal process. 
 
 ^■|\'ascular markings. 
 
 sp. Free spondylium or cast of it. 
 
 t. Teeth, 
 vs. Vascular sinus. 
 
 FlNKELNBURGIA OSCEOLA (Walcott) ()). 7'. 15). 
 
 Figures 1 and lb. Natural cauls of ventral valves from Locality 78, Upper Cambrian .sandstone in quarry near St. 
 
 Croix River, in suburbs of Osceola, Polk County, WLscon.sin. U. S. Nat. Mils. Cat. Nos. 52413a and 
 
 52413b, respectively. 
 la. Natural cast of ventral valve from Locality 79b, Upper Cambrian sandstone near Hudson, St. Croix 
 
 County, Wisconsin. U. S. Nat. Mus. Cat. No. 52415a. 
 Ic and 1(1, Id', and Id". Casts of the interior of a dorsal and a ventral valve from Locality 83', Upper Cam- 
 brian sandstone near Trempealeau, Trempealeau County, Wisoon,sin. U. S. Nat. Mus. Cat. Nos. 
 
 52412a and 52412b, respectively. Figure Id represents the type specimen, 
 le. Natural mold of exterior of dor.sal vahe associated with the specimens represented by figures Ic and Id. 
 
 U. S. Nat. Mus. Cat. No. 52412c. 
 If. Cast of interior of dor.sal valve that shows casts of what may have been the points of attachment of the 
 
 adductor muscles, associated with the specimens represented by figures Ic and Id. U. S. Nat. Mus. 
 
 Cat. No. 52412d. 
 Ig. Cast of the interior of dorsal valve as.sociated with the specimens represented by figures Ic and Id. . U. S. 
 
 Nat. Mus. Cat. No. 52412e. 
 Ih. Imperfect cast of the inferior of a dorsal valve from Locality 79a, Upper Cambrian sandstone at Menomo- 
 
 nie, Dunn County, Wisconsin. U. S. Nat. Mus. Cat. No. 52414a. 
 
 FiNKELNBURGIA FINKELNBLTJOI (Walcott) (j). 794). 
 
 Figure 2. Cast of interior of ventral valve, the type specimen. What may be the cast of the base of the \asciilar 
 
 trunks is .shown (vs). U. S. Nat. Mus. Cat. No. 52410a. 
 2a. Cast of interior of ventral valve, with outline of posterior view, showing area of adductor scars (a'). 
 
 U. S. Nat. Mus. Cat. No. 52410b. 
 2b. Cast of the interior of a ventral valve. U. S. Nat. Mus. Cat. No. .52410c. 
 2c. Cast of the inferior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52410d. 
 2d. Cast of the inferior of a ventral valve with the bases of very large vascular sinuses. U. S. Nat. Mus. Cat. 
 
 No. 52410e. 
 2e. Cast of interior of dorsal valve, with back and .side outlines. U. S. Nat. Mus. Cat. No. 52410f. 
 
 The specimen represented by figure 2 is from Locality 83, and those by figures 2a-c are from Locality 83'. a slightly 
 lower horizon, both in the Upper Cambrian sandstone near Trempealeau. Tremjiealeau County, ^\'iscon^in. 
 
 EooRTiiis? DIABLO (Walcott) (p. 77s). 
 
 Figure 3. Cast of interior of ventral valve, the type specimen, from Locality 81b, Upper Cambrian sandstone near 
 Devils Lake, Sauk ('ounty, Wisconsin. U. S. Nat. Mus. Cat. No. 52334a. 
 
 Otusla sandbergi (N. II. Winchell) (j). 769). 
 
 Figures 4 and 4a. Exterior of ventral valves. U. S. Nat. Mus. Cat. Nos. 3.5214a and 35214b, respectively. 
 4b. Interior of dorsal valve. U. S. Nat. Mus. Cat. No. 35214c. 
 4c and 4d. Inferior of the posterior part of a ventral valve. U. S. Nat. Mus. Cat. No. 35214d. 
 
 The specimens represented are all from Locality 302f, Upper Cambrian limestone on north side of Elk Pass, 
 Yellowstone National Park, Wyoming. 
 308 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH U PL. XCIII 
 
 =^RANCE8 WIESER DEt 
 
 MtLIOTVPE CO BOSTOM. 
 
PLATE XCIII. 309 
 
 Protorthis wingi Wal('ott (p. 743). 
 
 Figure 5. Distorted cast of interior of ventral valve. U. S. Nal. Mns. Cat. No. r)243Ta. 
 
 5a. Distorted ventral valve, the typo specimen, compreB.sed in argillaceous shale. U. S. Nat. Mus. Cat. No. 
 
 52437b. 
 oh and oc. Casts of distorted dorsal valves. U. S. Nat. Mus. Cat. Nos. •^)24.37c and .52437d, respectively. 
 
 The specimens represented are all from Locality 28, Ujjper Cambrian shales about 100 feet above the OUnellua 
 horizon south of Highgate Falls, 0.25 mile (0.4 km.) east of •Swanton, Franklin County, Vermont. 
 
 NisusiA (Jamesella) nautes (Walcott) (p. T.'A). 
 
 Figures and Oa. Exterior of ventral valves compressed and distorted in argillaceous shale of Locality 163, Middle 
 Cambrian Spence shale member of the Ute limestone in Spence Gulch, 15 miles (24.2 km.) west of 
 Montpelier, Bear Lake County, Idaho. U. S. Nat. Mus. Cat. Nos. 152432a and 52432b, respectively. 
 Figure 6 represents the type specimen. 
 6b. Interior of dorsal valve associated with specimens represented by figures and (ja. U. S. Nat. Mus. Cat. 
 No. 52432c. 
 
 Nisusia (Jamesella) spencei (Walcott) (p. 7.37). 
 
 [Text fig. 62, p. 737.] 
 
 Figure 7. Compressed ventral valve, from Locality llq. Middle Cambrian limestone in Ic of the Marjum limestone, 
 in ridge east of \\lieeler Amphitheater, IIou.sc Range, ITtah. U. S. Nat. Mus. Cat. No. 52436a. 
 7a. Compressed ventral valve, from Locality 163, .Middle (.'ambrian Spence shale member of the Ute limestone 
 in Spence Gulch, 15 miles (24.2 km. ) west of Montpelier, Bear Lake County, Idaho. U. S. Nat. Mus. 
 Cat. No. 52435b. This is the type specimen. 
 
PLATE XCIV. 
 
 311 
 
PLATE XCIV. 
 
 EooRTHis wiCHiTAENsis (Walcott) (p. 790). 
 
 [I'l. xciv.ng. lu.] 
 
 Figures 1 ami 1'. Exterior of ventral valve, the type specimen, and view of area, from Locality 12p. Upper Cam- 
 brian limestones, at the northwest extremity of the Arl)uckle Mountains. al)out 4 miles (0,4 km. I east 
 of Homer, Carter County, Oklahoma. U. S. Nat. Mus. Cat. No. 52384a. 
 
 laand la'. Exterior of ventral valve showingslight mesial fold, with side view. Locality 12k, Upper Cambrian 
 limestones in sec. 35, T. 1 S., R. 1 E., Ardmore quadrangle, Carter County, Oklahoma. U. S. Xat. 
 Mus. Cat. No. 52383a. 
 
 lb and lb'. Exterior of ventral valve associated with the specimen represented by figure 1, showing 
 flattened mesial area. U. S. Nat. Mus. Cat. No. 52384b. 
 
 Ic and Ic'. Exterior of ventral valve associated with the specimen represented by figure la. U. S. Nat. Mug. 
 Cat. No. 52383b. 
 
 Id. Exterior of ventral valve from Locality 71, Middle Cambrian limestone in Cold Creek Canyon, Burnet 
 County, Texas. U. S. Nat. Mus. Cat. No. 52379a. 
 
 le. Ventral valve partly exfoliated posteriorly so as to show cast of muscle area, associated with the 
 specimen represented by figure 1. U. S. Nat. Mus. Cat. No. 52384c. 
 
 If. Exterior of ventral valve, with straight cardinal slopes, associated with the specimen represented by 
 figure 1. U. S. Nat. Mus. Cat. No. 52384d. 
 
 Ig and Ih, Ih'. Exterior views of two dorsal valves illustrating variation in form and surface characters, 
 associated with the specimen represented by figure 1. U. S. Nat. Mus. Cat. Nos. 52384e and 52384f, 
 respectively. 
 
 li. Exterior of dorsal valve associated with the specimen represented by figure Id. U. S. Nat. Mus. Cat. 
 No. 52379li. 
 
 Ij. Ij', and Ik. Exteriors of two dorsal valves associated with the specimen represented by figure la. U. S. 
 Nat. Mus. Cat. Nos. 52383c and 52383d, respectively. 
 
 11 and Im. Dorsal valves associated with the specimen represented by figure 1. U. S. Nat. Mus. Cat. Nos. 
 52384g and 52384h. respectively. 
 
 In. Dorsal valve from Locality 12n, ITpper Cambrian limestones in sec. 1, T. 2 S., R. 1 E.. Ardmore quad- 
 rangle. Carter County, Oklahoma. U. S. Nat. Mus. Cat. No. 52381a. 
 
 lo. Cast of interior of a dorsal valve from Locality 68, Upper Cambrian limestone in Packsaddle Mountain, 
 Llano County, Texas. U. S. Nat. Mus. Cat. No. 52382a. 
 
 EOORTHIS WICHITAENSIS LiEVIUSCULUS (Walcott) (p. 791). 
 
 Figures Ip, Iq. Ir, and Is. Ventral, dorsal, side, and posterior views of the type specimen, a complete shell free from 
 matrix, from Locality 12p, ITpper Cambrian limestones, at the northwest extremity of the Arbuckle 
 Mountains, about 4 miles (6.4 km.) east of Homer, Carter County, Oklahoma. U. S. Nat. Mus. Cat. 
 No. 52396a. 
 
 EOORTHIS INDIANOLA (Walcott) (p. 780). 
 [PI. XCW.figs. 2, 2a-h.l 
 
 Figure It. Dorsal valve from Locality 12k, I'pper Cambrian limestones, Ardmore quadrangle. Carter County. Okla- 
 homa. U. S. Nat. Mus. Cat. No. 52343a. 
 
 Figure lu. Fragment of limestone from Locality 14b, Upper Cambrian limestone on Cold Creek, Llano County, Texas, 
 illustrating association of forms of Eoorthis wichiluensis (W) and Eoorthis indiannla (X). I^. S. Nat. 
 Mus. Cat. No. 52380a. 
 
 Eoorthis wichitaensis (Walcott) (p. 790;. 
 
 [PI. XCn'.flgs. l,la-o.I 
 
 Figure 1\i. Fragment of limestone from Locality 14b, Upper Cambrian limestone on Cold Creek, Llano County, Texas, 
 illustrating association of forms of Eoorthia wichitaensis (W) and Eoorthis indianola (X). U. S. Nat. 
 
 strating 
 Mus. Cat. No. 52380a 
 
 312 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XCIV 
 
 PC CS BOSTON 
 
PLATE XCIV. 313 
 
 EOORTHIS INDIANOLA (Walcott) (p. 7S0). 
 [PI. XCIV, figs. It-u.) 
 
 Figure 2. Exterior of a ventral valve, the type specimen, enlarged to show surface costje and strise. U. S. Nat. 
 
 Mus. Cat. No. 52343b. 
 2a. Exfoliated ventral valve showing cast of vi.sceral area. Locality 12p, Upper Cambrian limestones at the 
 
 northwest extremity of the Arlmckle Mountains, about 4 miles ( (1.4 km. ) east of Homer, Carter County, 
 
 Oklahoma. U. S. Nat. Mus. Cat. No. 52342a. 
 2b, 2b'; 2c, 2d, and 2e. Exterior of four ventral valves that vary in form and surface characters. U. S. Nat. 
 
 Mus. Cat. No. 52343c-f, respectively. 
 2f and 2f'. Exterior and side outline of dorsal valve. U. S. Nat. Mus. Cat. No. 52343g. 
 2g and 2g'. Ventral valve associated with the specimen represented by figure 2a. U. .S. Nat. Mus. Cat. No. 
 
 52342b. 
 2h. Exterior of dorsal valve. U. S. Nat. Mus. Cat. No. o2343h. 
 
 ■\\'ith the exception of figures 2a and 2g the specimens represented are all from Locality 12k, Upper Cambrian 
 limestones in sec. 35, T. 1 S., R. 1 E., Ardmore quadrangle. Carter County, Oklahoma. 
 
 EOORTHIS HASTINGSENSIS (Walcott) (p. 779). 
 
 Figures 3 and 3'. Exterior view and side outline of ventral valve from Locality 21, Middle Cambrian limestone at 
 the base of the Paradoxides zone on Hanford Brook, St. John County, New Brunswick. U. S. Nat. 
 Mus. Cat. No. 52337a. This is the type specimen. 
 
 3a. Diagrammatic outline of a vertical median section through the united valves of a specimen associated 
 with the ventral valve represented by figure 3. U. S. Nat. Mus. Cat. No. 52337b. 
 
 3b and 3c, 3c'. View of exterior of ventral and dorsal valves, with side outline of dorsal valve, from Locality 
 2s, Middle Cambrian limestone, at Hastings Cove, on Kennebeca.sis Bay, northeast of St. John, New 
 Brunswick. U. S. Nat. Mus. Cat. Nos. 52336a and 5233Gb, respectively. 
 
PLATE XCV. 
 
 315 
 
PLATE XCV." 
 
 a'. Anterior adductor scars. c. Crura, 
 
 a". Posterior adductor scars. j. Cardinal process, 
 
 b. Dental sockets. r. Diductor .soars. 
 
 EooRTiiis CHRisTiANLE (Kjerulf) " (p. 775). 
 
 Figure 1. Cast of e.Ktcrior of ventral valve. U. S. Nat. Mu.-<. Cat. No. 52.306h. 
 
 la, -lb, and Ic. Casts of ventral valves showing muscular area. U. S. Nat. Mus. Cat. Nos. 52306a-c, respec- 
 tively. 
 Id, le, and If. Casts of exterior of dorsal valves. U. S. Nat. Mus. Cat. Nos. 52.306d-f, re.spectively. 
 Ig. Cast of interior of dorsal valve. U. S. Nat. Mus. Cat. No. o230Gg. 
 
 The specimens represented by figures 1, la-gare from Locality 310d, Upper Cambrian Ceralopyge slate at Borghr)lm, 
 Oeland Lsland, Sweden. 
 
 Figure Ih. Dorsal valve with strong median sinus, from Locality 323x, Upper Cambrian Ceralopyge slate at Rus- 
 s?l6kken, near Christiania, Norway. U. S. Nat. Mus. Cat. No. 52307a. 
 
 EooRTHis DAUNUS (Walcott) '' (p. 776). 
 
 Figure 2. Ventral valve with side outline from Locality 310j, passage beds between the Upper Cambrian and the 
 
 Ordovician, Ceratopyge limestone at Borgholm, Oeland Island, Sweden. V. S. Nat. JIus. Cat. No. 
 
 52309a. 
 2a and 2b. Dorsal valves in limestone matrix of Locality 323z, passage beds between the Upper Cambrian and 
 
 the Ordovician, Ceratopyge limestone at Toien, near Christiania, Norway. L'. S. Nat. Mus. Cat. 
 
 Nos. 52308a and 52308b, respectively. Figure 2a represents the type specimen. 
 2c. Dorsal valve associated with the .specimen represented by figure 2. I'. S. Nat. Mus. Cat. No. 52309b. 
 
 EOORTHIS TULLBERGI (Walcott)" (p. 790). 
 
 FidURE 3. Partly exfoliated ventral valve, the type specimen, from Locality 390, passage beds between the Upper Cam- 
 brian and the Ordovician, at Alunbruk (alum works\ Oeland Island, Sweden. U. S. Nat. Mus. Cat. 
 No. 58309. 
 
 EooRTHis wiMAXi (Walcott) " (p. 791). 
 
 Figure 4. Cast of interior of ventral valve from Locality 8x, passage beds between the Upper Cambrian and the Ordo- 
 vician, Ceratopyge limestone at Slemmostad, about 3 miles (4.8 km.) southwest of Christiania, Norway. 
 U. S. Nat. Mus. Cat. No. 52311a. 
 
 4a. Cast of interior of dorsal valve, the type specimen, from Locality 323w, L'pper Cambrian lilack argil- 
 laceous shale of "Etage 3a/}" at Christiania, Norway. L'. S. Nat. Mus. Cat. No. 52;il3a. 
 
 4b. Exfoliated dorsal valve from Locality 310j, passage bids between the L'pper Cambrian and the Ordovician, 
 Ceratopyge limestone at Borgholm, Oeland Island, Sweden. V. S. Nat. Mus. Cat. No. 52312a. 
 
 4c and 4d. Ventral and dorsal valves associated with the specimen represented by figure 4a. V. S. Nat. Mus. 
 Cat. Nos. 52313b and 52313c, respectively. 
 
 Protorthis? hunnebergensis Walcott" (p. 740). 
 
 Figure 5. Cast in shale of exterior of ventral valve. U. S. Nat. Mus. Cat. No. .52428a. 
 
 5a. Cast of compressed ventral valve, the type specimen. U. S. Nat. Mus. Cat. No. 52428b. 
 5b. Cast in shale of exterior of dorsal valve. U. S. Nat. Mus. Cat. No. 52428c. 
 5c. Partial cast of interior of dorsal valve. U. S. Nat. Mus. Cat. No. 5242Sil. 
 
 The specimens represented are all from Locality ,390f, pa.ssage beds between the Upper Cambrian and the Ordo- 
 vician, shales at Mossebo, on Hunneberg, Province of Skaraborg, Sweden. 
 
 o A photograph of this plate was sent to Prof. J. C. Moberg, who reproduced It as Plate II ol his paper on the Ceralopyge region (Moberg and 
 
 Segerberg, 1900, I'l. 11]. 
 
 81 G 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XCV 
 
 PHANCES WIESeR DEL. 
 
 MCLiatVPE CO aOSTOM 
 
PLATE XCV. 817 
 
 EOSTROPIIOMENA ELEGANTULA (Willcott)" (p. 796). 
 
 Figure 6. Exterior of ventral valve, the type specimen. U. S. Nat. Mu.s. Cat. No. 5231Ga. 
 6a. Tartly exfoliated dorsal valve. U. S. Nat. Mus. Cat. No. 52316b. 
 
 6b. Cast of Interior of dor.sal valve. All elevations and depressions are the reverse of their actual occurrence 
 in the interior of the shell. U. S. Nat. Mus. Cat. No. 52316c. 
 
 The specimens represented are all from Locality 310j, passage beds between the Upper Cambrian and the Ordo- 
 vician, Ccrafopyge limestone at Borgholm, Oeland Island, Sweden. 
 
 EooKTHis ATAVA (Matthew)" (p. 774). 
 
 Figures 7 and 7a. Ventral valves. Figure 7 represents the type specimen. 
 7b. Dorsal valve. 
 
 The specimens represented are all from Localily 308a, Upper Cambrian shales of Division C3a of Matthew at Navy 
 Island, St. John Harbor, St. John, New Brunswick. The figures (7, 7a-b) are redrawn from the specimens illustrated 
 by Matthew [1893, PI. VII, figs. 8c, 8a, and 8b, respectively]. 
 
 a A photograph of this plate was sent to I'rot. J. C. Moberg, who reproduced it as Plate U of his paper on the Ceralopyge region [Moberg and 
 Segerberg, 1906, PI. IIJ. 
 
PLATE XCVI. 
 
 319 
 
PLATE XCVI. 
 
 c. Crura. ps. Pseudospondylium. 
 
 j. Cardinal process. s. Median septum, 
 
 t. Teeth. 
 
 EooRTHis DESMOPLEURA (Meek) (p. 777). 
 
 FiGBRES 1; la, la'; lb; and If. Exterior and side view.s of four ventral valvep, illustratinj; variation in form and 
 surface characters. Locality 187, Lower Ordovician red siliceous limestone 105-122 feet above the 
 pre-Cambrian, 2 miles (3.2 km.) below JIanitou Park Hotel, El Paso County, Colorado. L'. S. Nat. 
 Mus. Cat. Xos. 52317a-d, re.spectively. 
 
 Id and le. Cast of ventral valve associated with the specimen represented by figure 1, with side outline, show- 
 ing area and cast of umbonal cavity. U. S. Nat. Mus. Cat. No. 52317e. 
 
 If and Ig. Dorsal valves associated with the specimen represented by figure 1. V. S. Nat. JIus. Cat. Nos. 
 52317f and 52317g, respectively. 
 
 Ih. Silicified shell showing character of radiating costse and stria;. This is the type specimen, from Locality 
 360f, Lower Ordo\'ician siliceous limestone at Glen EjTe, Camp Creek Canyon, near Manitou, El 
 Paso County, Colorado. V. S. Nat. Mus. Cat. No. 7859a. 
 
 li and Ij. Top and side views of ventral valves from Locality 14k, I^pper Cambrian limestone on Wolf Creek. 
 15 miles (24.2 km.) west -southwest of Sheridan, Sheridan County, Wyoming. U. S. Nat. Mus. Cat. 
 Nos. 52320a and 52320b, respectively. 
 
 Ik and 1 1. Exterior of dorsal calves associated with the dorsal valves represented by figures li and Ij. U. S. 
 Nat. Mus. Cat. Nos. 52320c and 52320d, respectively. 
 
 Im and In. Exterior of small ventral valves. U. S. Nat. Mus. Cat. Nos. 52319a and 52319b, respectively. 
 
 lo. Exterior of a ventral valve. V. S. Nat. Mus. Cat. No. 52319c. 
 
 Ip. Side view of a young, convex shell. V . S. Nat. Mus. Cat. No. 52319d. 
 
 Iq. Posterior portion of the interior of an abraded ventral valve. L'. S. Nat. Mus. Cat. No. 52319e. 
 
 Ir. Interior of an abraded dorsal valve. U. S. Nat. Mus. Cat. No. 52319f. 
 
 The specimens represented by figures Im-r are from Locality 168, Middle Cambrian limestones on Tepee Creek, 
 near the road from Sheridan to Dome Lake, Bighorn Mountains, Wyoming. 
 
 EOORTHIS DESMOPLEURA NYMPHA (Walcott) (p. 778). 
 
 Figure 2. Exterior and side views of a \-entral \ahe, the type specimen, from Locality 168, Middle Cambrian lime- 
 stones on Tepee Creek, near the road from Sheridan to Dome Lake, Bighorn Jlountains, ^^■yoming. 
 U. S. Nat. Mus. Cat. No. 52333a. 
 
 Plectorthis whitfieldi (X. H. Winchell) (p. 308). 
 
 Figure 3. Interior of a ventral valve, showing the relatively high area and strong teeth, the outline of the pseudo- 
 spondylium, and the low ridges extending forward and outward from its anterior margin. Ordovician, 
 Spring Valley, Minnesota. Copied from Hall and Clarke [lS92c, PI. V, fig. 26]. 
 
 Plectorthis plicatella (Hall) (p. 772). 
 
 [Text fig. 12, p. 299.] 
 
 Figure 4. Posterior portion of the interinr of a \i'ntral valve, showing the broad delthyrium. teeth, and the outline 
 of the pseudospondylium. 
 4a. The area of the dorsal valve, showing the triangular delthyrium, cardinal process, crural plates, and low 
 narrow median ridge. 
 
 The specimens represented are all from the Ordovician at Covington, Keritu<ky. The figures are copied from Hall 
 and Clarke [1892c, PI. V, figs. 19 and 20]. 
 320 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XCVI 
 
 ^ 
 
 ilA-i*^- 1 'iJiL 
 
 '^ikH^h^..^ \ 
 
 
 
 <^m 
 
 ,^ f/^ 
 
 "^iiX'l 
 
 i^ii 
 
 
 5" 
 
 ^ 
 
 u 
 
 i > 
 
 0') m 
 
 
 FRANCES WiESER DEL. 
 
 ELIOTVPC CO eOSTOM 
 
PLATE XCVI. 321 
 
 Plectorthis jamesi (Hall) (p. 772). 
 
 Figure 5. Exterior of a ventral valve. U. S. Nat. Mus. Cat. No. 51307a. 
 5a. Interior of a ventral valve. U. S. Nat. Mus. Cat. No. 513C7b. 
 5b. Interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 51307c. 
 
 5c. View of the interior of the specimen represented by figure 5b over the front margin so as to obtain a front 
 view of the cardinal process and crural plates. 
 
 The specimens represented are all from Ordovician beds of Lorraine age at Cincinnati, Ohio, and the figures are 
 introduced here for comparison. 
 
 Plectorthis parva (Dalman) (p. 776)." 
 
 Figure 6. Exterior of a ventral valve, to illustrate form and surface ribs. U. S. Nat. Mus. Cat. No. 52314a. 
 
 6a-d. Side views of four specimens having the two valves united, to illustrate the variation in the convexity 
 
 of young and adult shells. U. S. Nat. Mus. Cat. Nos. 52314b-e, respectively. 
 6e. Interior of a ventral valve. U. S. Nat. Mus. Cat. No. 52314f. 
 6f. Interior of a dorsal valve.. U. S. Nat. Mus. Cat. No. 52314g. 
 6g. Enlargement of the posterior portion of the interior of a dorsal valve, to show the small cardinal process, 
 
 etc. U. S. Nat. Mus. Cat. No. 52314h. 
 
 The locality and horizon of the specimens represented are unknown. 
 
 a See Eoorthis christianix, p. 776. 
 62667°— VOL 51, pt 2—12 21 
 
PLATE XCVII. 
 
 323 
 
PLATE XCVII. 
 
 EooRTHis PRiMORDiAi.is (tie \'cnicuil and Biiriando) (p. 785). 
 
 FicJURE I. Ventral view of the type specimen, having the two valves nnited. 
 la. Dorsal view of the specimen represented by figure 1. 
 
 lb. The same, seen from the side. The area of the dorsal valve is a little loo .short. 
 Ic. The same, posterior view. 
 Id. The same, seen from the front side. Most of our specimens are less thick. 
 
 The specimen represented is from Locality 350, Middle Cambrian limestone near Adrados, Cantabrian Mountains, 
 Province of Leon, Spain. The figures are 'copied from de Verneuil and Harrande [1860, PI. VIII, figs. G, Ca-<1]. 
 
 NisusiA (Jamesella) pellico (dc Verneuil and Barrande) (p. 735). 
 
 Figure 2. Ventral view of the type specimen, showing area and deltidiuin. 
 2a. Dorsal view of the specimen represented by figvire 2. 
 2b. Posterior view of same, showing areas of valves. 
 
 The specimen represented is from Locality 350, Middle Cambrian limestone near Adrados, Cantabrian Mountains, 
 Province of Leon, Spain. The figures are copied from de Verneuil and Harrande [18(i0. PI. VII, figs. 7, 7a-b]. 
 
 NiSUSiA ? VATICINA (de Yeiiieiiil and Barrande) (]). 7.30). 
 
 Figure 3. Dorsal view of the type specimen, with the two valves united, showing the area of the ventral valve. 
 3a and 31). Posterior and side views of same shell. 
 
 The specimen represented is from Locality 350, Middle Cambrian limestone near Adrados, Cantabrian Mountains, 
 Province of Leon, Spain. The figures are cojjied from de Verneuil and Barrande [1800, PI. A'lII, figs. S, Sb-c]. 
 
 EooRTHis BAVARICA (Barrande) (p. 775). 
 
 Figure 4. A distorted ventral valve, the type specimen, from Locality 303c, passage beds between the Upper Cam- 
 brian and Ordovician, suburbs of Hof, Bavaria. Copied from Barrande [1868a, fig. 76]. 
 
 EooRTHis LiNNARSSONi (Kayser) (p. 782). 
 
 Figure 5. Dorsal valve from Locality C64, Upper Cambrian limestone 2.7 miles (4.4 km.) southwest of Yenchuang, 
 Sintai district, Shantung, China. U. S. Nat. Mus. Cat. No. 52.549a. 
 5a. Ventral and dorsal valves from Locality 332a, LTpper Cambrian at Taling. Liaotung, China. Type 
 specimen copied from Kayser [1883, PI. Ill, fig. 1]. 
 
 EooRTHis KAYSERi (Walcott) (j). 782). 
 
 Figure 6. Partly exfoliated, distorted ventral valve. U. S. Nat. Mus. Cat. No. 52546a. 
 
 6a. Partly exfoliated dor.sal valve, the tyi)e specimen. U. S. Nat. Mus. Cat. No. 52546b. 
 Gb. Cast of tlic interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52546c. 
 
 The specimens represented are all from Locality 064, I'jjper Cambrian limeslone 2.7 miles (4.4 km.) southwest of 
 Yenchuang, Sintai district, Shantung, China. 
 
 BiLLiNGSELLA iiicKsi (Saltef MS.) (Davidsoii) (p. 756). 
 
 Figures 7 and 7a. Ventral and dorsal views of the type specimen. 
 7b. Cast of ventral valve. 
 
 The specimens represented are from Localities 318d and 318p, Middle Caml)rian sandstones in the Menevian at 
 Porth-y-rhaw and Ninewells, near Si. Davids, South Wales; Davidson does not say which. Figures 7, 7a-b are copied 
 from Davidson [1869, PI. XXXIII, figs. 14a, 13a, and IGa, resi)ectively]. 
 324 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XCVII 
 
 FRANCES WIESER DEL. 
 
 MELIOTVPE CO., BOSTON 
 
PLATE XCVII. 325 
 
 B1LLINGSELI.A puMPELLYi Walcott (p. 760). 
 
 Figure 8. Top and side view of partly exfoliated ventral valve, the type specimen, from Locality C61, Upper Cam- 
 brian limestone 3 miles (4.8 km.) southwest of Yenchuang, Sintai district. Shantung, China. U. S. 
 Nat. Mus. (.'at. No. .52.558a. 
 
 8a. Top and side view of cast of a ventral valve from Locality C36, Upper Cambrian Chaumitien limestone 
 at Chaumitien, Changhia district, Shantung, China. U. S. Nat. Mus. Cat. No. 52557a. 
 
 8b. Interior of dorsal valve associated with the specimen represented by figure 8a. U. S. Nat. Mus. Cat. 
 No. 52557b. 
 
 8c. Enlargement of outer surface, near front margin, of a shell associated with the specimen represented by 
 figure 8. V. S. Nat. Mus. Cat. No. 52.558b. 
 
 EooRTHis NEWTONENsis (Weller) (p. 784). 
 
 Figures 9 and 9a. Cast of interior of ventral and dorsal valves, with side outline of ventral valve (9'), from Locality 
 lie, Upper Cambrian Uardyston quartzite, O'Donnell and McManniman's quarry, Newton, Sussex 
 County, New Jersey. U. S. Nat. Mus. Cat. Nos. 52352a and 52352b, respectively. 
 
 EooRTHis jOHANNENsis (Matthew) (p. 781). 
 
 Figure 10. Top and side views of ventral valve, the type specimen. University of Toronto, Canada. 
 10a. Top and side views of dorsal valve. University of Toronto, Canada. 
 
 The specimens represented are both from Locality 308b, Upper Cambrian limestone in shales of Division C3a of 
 Matthew, Germaine Street, St. John, St. John County, New Brunswick. The figures are redrawn from the specimens 
 illustrated by Matthew [1892, PL XII, figs. 13a-c] as Orthisina (?) johannensh. 
 
 EooRTHis SALTENsis (Kayser) (p. 788). 
 
 Figure 11. Group of .-ihells on fragment of rock from Locality 389, Upper Cambrian sandstone at Salta, Argentina. 
 Type specimen, copied from Kayser [1876, PL I, fig. 16]. 
 11'. Casts of two ventral valves on fragment of rock from Locality 389a, Upper Cambrian sandstone at Nevado 
 de Castillo, Province of Salta, Argentina. Copied from Kayser [1876, PI. I, fig. 15]. 
 
 EooRTHis PAGODA (Walcott) (p. 784). 
 
 Figures 12 and 12a. Partly exfoliated ventral \-alves. U. S. Nat. Mus. Cat. Nos. 52552a and 52552b, respectively. 
 Figure 12 represents the type specimen. 
 12b. Partly exfoliated dorsal valve. U. S. Nat. Mus. Cat. No. 52552c. 
 12c. Interior of dorsal valve. U. S. Nat. Mus. Cat. No. 52552d. 
 12d. Enlargement of a portion of the outer surface of the shell. U. S. Nat. Mus. Cat. No. 52552e. 
 
 The specimens represented are all from Locality C56. Upper Cambrian ( hauniitien limestone at Pagoda Hill, 
 1 mile (1.6 km.) west of Tsinan, Shantung, China. 
 
 EooRTHis DORIS (Walcott) (p. 779). 
 
 Figure.s 13 and 13a. Top and side views of two ventral valves from Locality C64, Upper Cambrian limestone 2.7 miles 
 (4.4 km.) southwest of Yenchuang, Sintai district. Shantung, China. U. S. Nat. Mus. Cat. Nos. 52.551a 
 and 52551b, respectively. Figure 13a represents the type specimen. 
 
 NisusiA COMPTA (Tate) (p. 727). 
 
 Figure 14. Top and side views of the type specimen of the .species from Locality 315, Middle? Cambrian limestone 
 at Curramulka, Yorke Peninsula, South Australia. University of Adelaide, South Australia. Speci- 
 men figured by Tate 1 18112, PI. II, figs. 6 and 6a] as Orlhisina compta. 
 
 EooRTHis TATEi (Etlieridge) (p. 789). 
 
 Figure.? 15, 1.5', and 1.5a, 1.5a'. Top and side views of ventral and dorsal valves from Locality 315b, Middle? Cambrian 
 limestone at Wirrialpa, Flinders Range, South Australia. University of Adelaide, South Australia. 
 Figures 15 and 15a are redrawn from the specimens illustrated by Etheridge [1905, PL XXV, figs. 
 7 and 8, respectively]. Figure 15a represents the type specimen. 
 
PLATE XCVIII. 
 
 327 
 
PLATE XCVIII. 
 
 Orusia lenticularis (Walilenberg) (p. 765). 
 
 [I'l. XCVIII, Hgs.fi.Oa-o.) 
 
 Figures 1; la, la'; and lb. Exterior surface of ventral valves, illustrating variation in radial costse, with side outline 
 of specimen represented by figure la. Locality 3S0n, Upper Cambrian limestone at Hunneberg, 
 Province of Skaraborg, Sweden. U. S. Nat. Mus. Cat. Nos. 52400a-c, respectively. 
 
 Icand Ic'. Top and posterior \aews of \'entral \'alve associated vrilh the specimens represented by figures 
 1, la-h. Figures Ic and 2b represent forms having the characters of Matthew's "Orusia lenticularis 
 strophomenoides." V. S. Nat. Mus. Cat. No. 52400d. 
 
 Id and Id'. Top and side views of a smooth ventral valve associated with the specimens represented by 
 figures 1, la-b. U. S. Nat. Mus. Cat. No. 52400e. 
 
 le and le'. Natural mold of the interior of ventral valve, with posterior outline. Locality 310a, Upper ( am- 
 brian shales of Olenus truncatus zone on Oeland Island, Sweden. U. S. Nat. Mus. Cat. No. 52406a. 
 
 If, If, and If". Top, side, and posterior views of a very smooth ventral valve associated with the specimen 
 represented by figure le. U. S. Nat. Mus. Cat. No. 5240Gb. 
 
 Ig and Ig'. Top and side views of a dorsal \alve associated with the specimen represented by figure le. U.S. 
 Nat. Mus. Cat. No. 52406c. 
 
 Ih, li, Ij, Ik, 1 1, Im, In, and lo. Series of dorsal valves and side outlines illustrating variation in form of 
 shell and character of surface. Locality 390n, Upper Cambrian limestone at Hunneberg, Province 
 of Skaraborg, Sweden. U. S. Nat. Mus. Cat. Nos. 52400f-m, respectively. 
 
 Ip. Cast of the interior of a small ventral valve, showing the extension of the main vascular sinuses back 
 across the umbonal cavity; also the division of the muscle area between them by a narrow septum. 
 This specimen is in the tray with the specimens represented by figures le-g, but none of the speci- 
 mens received locality numbers when they were first collected and the locality may be con.sidered 
 doubtful. U. S. Nat. Mus. Cat. No. 52406d. 
 
 2 and 2'. Top and side views of a ventral valve from Locality 3, Upper Cambrian limestone 300 feet above 
 the Paradoxides zone on Manuels Brook, Conception Bay, Newfoundland. U. S. Nat. Mus. Cat. 
 No. 52402a. 
 
 2a. Ventral valve, with numerous radiating costse, from Locality 6v, L^ppcr Cambrian limestones 325 feet 
 above the Middle Cambrian on Manuels Brook, Conception Bay, Newfoundland. U. S. Nat. Mus. 
 Cat. No. 52404a. 
 
 2b. A small, very convex, and rugose ventral valve in which the radiating costse are nearly obliterated, 
 associated with the specimen represented by figure 2a. Figures Ic and 2b represent forms having 
 the characters of Matthew's " Orusia hnlicularis strophomenoides." U. S. Nat. Mus. Cat. No. 52404b. 
 
 2c and 2d. Compressed ventral valves associated with the sj)ecimen represented by figure 2. U. S. Nat. 
 Mus. Cat. Nos. 52402b and 52402c, respectively. 
 
 2c'. Side outline of specimen represented by figure 2o. 
 
 2e, 2f, 2h, 2i, and 2j. Series of dorsal valves associated with the specimen represented by figure 2, illus- 
 trating variation in form of shell and surface characters. U. S. Nat. Mus. Cat. Nos. 52402d-h, 
 respectively. 
 
 2f'. Posterior view of specimen represented by figure 2f. 
 
 2g. Dorsal valve associated vrith the specimen represented by figure 2a. U. S. Nat. Mus. Cat. No. 52404c. 
 
 2k. Compressed ventral valve associated with the specimen represented by figure 2. V. S. Nat. Mus. Cat. 
 No. 524021. 
 
 3. Enlargement of a fragment of shale on which the shells show a considerable variation. 
 
 3a and 3b. Ventral and dorsal valves. 
 
 The specimens represented by figures 3, 3a-b are in the collection of the Univer.«ity of Toronto, Canada, and sire 
 labeled as coming from St. John, New Brunswick. They are among the material used by Matthew in drawing figures 
 9a-<l of his paper [1892, PI. XII], but closer identification is impossible. 
 
 Orusia lenticulaki.s ly.ncioides (MatUiew) (p. 769). 
 
 Figure 4. Ventral valve from Lcxality 308b. I'pik r Cambrian lim(sli>ne in shales of Dix-ision C3a of Matthew, Gor- 
 maine Street, St. John, New Brunswick. University of Toronto, Canada. Type specimen figured 
 by Matthew [1892, PI. XII, fig. lOaJ. 
 328 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH l; PL XCVIM 
 
 PRANCES WIESER DEL. 
 
 PC c:: sosroN 
 
PLATE XCVIII. 329 
 
 Orusia lenticularis atrypoides (Matthew) (p. 769). 
 
 Figure 5. Ventral valve from Locality 308b, Upper Cambrian limestone in shales of Division C3a of Matthew, Ger- 
 maine Street, St. John, New Brunswick. University of Toronto, Canada. Type specimen figured 
 by Matthew [1892, PI. XII, fig. 11a]. 
 
 Orusia lenticxjlaris (Wahlenberg) (p. TG.'S). 
 
 [PI. XCVIII, figs. :,la-p; 2,2a-k; and .3,3a-l>.) 
 
 Figures 6, 6a-c. Ventral, dorsal, side, and po.sterior views of a specimen from Locality 3, Upper Cambrian limestones 
 300 feet above the Paradoxides zone on Manuels Brook, Coneeption Bay, Newfoundland. U. S. 
 Nat. Mus. Cat. No. 52402J. 
 
PLATE XCIX. 
 
 331 
 
PLATE XCIX. 
 
 a. Cardinal area. f. Cast of dental sockets. 
 
 b. Dental sockets. pc. rseudocTuraliiim. 
 
 d. Delthyrium. sp. Free spondylium or cast of it. 
 
 d'. Cast of didnctor scars. t. Teeth. 
 
 Protorthis billingsi (Hartt) (p. 739). 
 
 Figure 1. Cast of ventral valve from a natural mold, in which the area i.s compressed and crowded backward. V. S. 
 
 Nat. Mus. Cat. No. 52424a. 
 la. Natural cast of compressed ventral valve. U. S. Nat. Mus. Cat. No. 52424b. 
 lb, lb', and Id, Id'. Top and back views of natural casts of compressed ventral valves in which the area is 
 
 shown. Id' shows the cast of the spondylium. T. S. Nat. Mus. Cat. Nos. 52424c and 52424d, 
 
 respectively. 
 Ic. Natural cast of a compressed ventral valve (locality unknown). University of Toronto, Canada, 
 le and If. Natural casts of compressed dorsal valves. U. S. Nat. Mus. Cat. Nos. 52424e and 52424f, 
 
 respectively. 
 Ig. Natural cast of the outer surface of a small dorsal valve. U. S. Nat. Mus. Cat. No. 52424g. 
 
 With the exception of figure Ic the specimens represented are all from Locality 3b, Middle Cambrian shale, head 
 of Seeley Street, St. John, St. John County, New Brunswick. None of them has been figured before. 
 
 Protorthis quacoensis (Matthew) (p. 742). 
 
 Figure 2. Exterior of a compressed ventral valve. 
 
 2a. A minute ventral valve referred to this species. 
 
 2b. Top, side, and posterior views of the cast of an uncompressed ventral valve, showing elevation, cardinal 
 
 area, and deltidium. Type specimen, figured by Matthew [1886, PI. V, figs. 20b and 20c]. 
 2c. An uncompressed dorsal valve, with posterior and side view in outline. 
 2d. Dorsal \a\ve distorted by compression and movement in the shale. 
 2e. Top and posterior views of the cast of a dorsal valve. Specimen figured by Matthew [18S6, PI. V, figs. 
 
 20 and 20a]. 
 
 The specimens represented are from Division Ic of Matthew's Etcheminian, but Matthew does not state [1886, 
 pp. 44 or 82] whether they are from Porters Brook (Locality 301mi or Portland (Locality SOlgi. St. John County, 
 New Brunswick. They are all in the collections of the University of Toronto, Canada. 
 
 Protorthis latourensls (Matthew) (p. 741). 
 
 Figures 3 and 3'. Mold of interior of a dorsal? valve, with side outline (locality unknown"). University of Toronto, 
 
 Canada. 
 3a. Matrix in fine shale of the exterior of a ventral valve from Locality 308h, Middle Cambrian shales of 
 
 Division Icl at Portland, St. John, New Brunswick. U. S. Nat. Mus. Cat. No. 1818.5a. 
 3b. Posterior view of mold of a ventral valve showing mold of spondylium (locality unknown). Uni\ersity 
 
 of Toronto, Canada. 
 3c. Posterior view of the mold of a ventral valve (locality unknown). University of Toronto, Canada. 
 3d. Matrix of exterior of a dorsal valve from Locality 301w, Middle Cambrian shales of Division ]c2 of Matthew 
 
 ut Portland, St. John, New Brunswick. U. S. Nat. Mus. Cat. No. 18168a. 
 
 Figures 3, 3b, and 3c were drawn from specimens in Matthew's original material, but none of the Bpecimens 
 represented by Matthew in figures IS, 18a-c [18S(i, PI. V] is redrawn in this monograph. 
 
 Protorthis Helena Walcott (p. 740). 
 
 Figure 4. Cast of ventral valve, the type specimen, from Locality 2u, Middle Cambrian shale on south side of Long 
 Island, Kennebccasis Bay, St. John County, New Brimswick. U. S. Nat. Mus. Cat. No. -524273. 
 4a and 4b. Side and back views of the specimen represented by figure 4. 
 332 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. XCIX 
 
 FRANCES WIE8ER DEL. 
 
 MEllOTyCC CO SOSTOm 
 
PLATE XC'IX. 333 
 
 Pkotorthis (Loperia) dugaldensis Walcott (]).744). 
 
 Figures 5, 5', and 5". Top, side, and posterior views of a niolil of ihe interior of a ventral valve, the type specimen. 
 
 IT. S. Nat. Mua. Cat. No. 52440a. 
 5a. A compressed and distorted ventral valve from Locality 2u, Middle Cambrian, south side of Long Island, 
 
 Kennebecasis Bay, St. John County, New Brunswick. LT. S. Nat. Mus. Cat. No. 52446a. 
 5b. Side outline of the natural mold of a ventral valve. U. S. Nat. Mus. Cat. No. 52440b. 
 5b'. View looking from front margin toward the area and spondylium, as shown in a cast of a ventral valve. 
 
 Same specimen as represented by figure 5b. 
 5c and 5c'. Top and side views of the natural mold of a ventral valve. The outline 5c' shows the position of 
 
 the short spondylium just beneath the beak. U. S. Nat. Mus. Cat. No. 52440c. 
 5d; 5e, 5e'; 5f, 5f'; 5g; and 5h, 5h'. Top and side views of natural molds of five dorsal valves, V. S. Nat. 
 
 Mus. Cat. Nos. 52440d-h, respectively. 
 51. Enlargement of the outer surface obtained by making a cast from the matrix of the surface. U. S. Nat. 
 
 Mus. Cat. No. 524401. 
 5j. Exterior of a ventral valve, drawn from impressions obtained in a natural matrix. U. S. Nat. Mus. Cat. 
 
 No. 52440]. 
 
 The specimens represented by figs. 5, 5b-j (not 5a) are from Locality lOp. Middle Camlirian sandstones of Division 
 E2b of Matthew on Dugald Brook, Indian River, Cape Breton, Nova Scotia. 
 
 Protorthis Levis' Walcott (p. 741). 
 
 Figures 6, 6a, and 6b. Top, back, and side views of the type specimen, from Locality 79a, Upper Cambrian "St. 
 Croix sandstone" 0.5 mile (0.8 km.) southeast of the county courthouse, Menomonle, Dunn 
 County, Wisconsin. I'. S. Nat. Mus. Cat. No. 52429a. 
 
PLATE C. 
 
 335 
 
PLATE C. 
 
 a. Cardinal area. d'. Cast of pscudocniralium. 
 
 1). Dental sockets. e. Adduclor soars. 
 
 c. Crura. >■• Diductor scars, 
 cr. Pseudoeruraliuni. t. Teeth. 
 
 d. Deltidium. ^- Flexure line. 
 
 NiSUSIA FESTINATA (Billuigs) (p. 727). 
 [Text flg. (i, p. 299.] 
 
 Figure 1. Exterior of ventral valve, drawn from mold taken in a natural cast. U. S. Nat. Mus. Cat. Xo. 52288a. 
 
 la. Cast of ventral valve from Locality 26a, Lower Cambrian limestone 2 miles (3.2 km.) ea-st of Swanton, 
 
 Franklin County, Vermont. U. S. Nat. Mus. Cat. Xo. 153.38a. Specimen figured by Walcott 
 
 [188(ib. PI. VII, fig. 7]. 
 lb, lb', and lb". Top, side, and back views of cast of transvcr.-^e ventral valve. U. S. Nat. Mus. Cat. Xo. 
 
 62288b. 
 Ic and Ic'. Top and side views of cast of elevated ventral valve, willi strongly marked cost«. U. S. Nat. 
 
 Mus. Cat. No. 52288c. 
 Id and Id'. Top and back views of cast of ventral valve, an intermedialo form lietween those represented 
 
 l)y figures lb and Ic. U. S. Nat. Mus. Cat. No. 52288d. 
 Id". Side view of ventral valve, with finer cost;* than that represented liy ligure Id. U. 8. Nat. Mus. Cat. 
 
 No. 52288e. 
 le, le'. and le". Top, side, and back views of a cast taken in a tialural mold of a ventral valve, in which 
 
 the area slopes forward. U. S. Nat. Mus. Cat. No. 52288f. 
 If and IF. Top and side views of a cast of a dorsal valve. U. S. Nat. Mus. Cat. No. 52288g. 
 Ig. Cast of the interior of a large dorsal valve. The reference of the markings at "e" as adductor scars is 
 
 doubtful. U. S. Nat. Mus. Cat. No. 52288h. 
 Ih and Ih'. Top and liack views of a small ventral valve, from Locality 26, Lower Cambrian sandstone east 
 
 of Highgate Springs, Franklin County, Vermont. U. S. Nat. Mus. Cat. No. 15362a. Specimen 
 
 figured liy Walcott [1886b. PI. VII, figs. 7a-l)]. 
 li and li'. Top and side views of cast of a small transverse dorsal valve. L'. S. Xat. Mus. Cat. No. 52288i. 
 Ij. Interior of a ^•entral \-alve drawn from a cast of a natural mold. L". S. Nat. Mtis. Cat. No. 52288J. 
 
 With the exception of specimens shown liy figures la and Ih, all of the specimens represented by figiu-es 1. la-j 
 are from Locality 49, Lower Cambrian decomposed arenaceous limestones on Codorus Creek, below Meyer's mill, near 
 Emigsville, Pennsylvania. 
 
 Figures 2, 2'; 2a, 2a'; and 2b, 2b'. Top and side views of three ventral valves from Locality 2o, Lower Cambrian 
 conglomeratic limestones at Bic, Province of Quebec, Canada. U. S. Xat. Mus. Cat. Nos. 52291a, 
 52291b, and 52291c, respectively. 
 2c, 2c'. and 2c". Top, posterior, and side views of a ventral valve, with point of the apex broken off. Asso- 
 ciated with the specimens represented by figures 2, 2a-b. U. S. Nat. Mus. Cat. No. .52291d. 
 
 NiSUSIA ALBERTA (Walcott) (p. 726). 
 
 Figure 3. Top and side ^dewof a cast of a ventral valve. It is attached to the dorsal valve shown in figure 3a. 
 U. S. Nat. Mus. Cat. No. 24070a. The type specimen is represented by figures 3, 3a-b. 
 
 3a. View of a cast of a dorsal valve, and the area of the ventral valve shown in figure 3. V. S. Xat. Mus. Cat- 
 No. 24070a. 
 
 3b. Posterior view of the ventral and dorsal valves represented by llgm-es 3 and 3a. U. S. Nat. Mus. Cat. 
 No. 24070a. 
 
 3c. Cast of exterior surface showing ribs and stout bases of spines. V . S. Nat. Mus. ( 'at. Xo. 240701). Copied 
 from Walcott [1908c, PI. I, fig. 4]. 
 
 3d. Interior of the largest shell seen. Geol. Survey Canada. Cojued from Walcott [1908c, PI. I, fig. 4a]. 
 
 The specimens represenled are all from Locality 14s, Middle Cambrian ()<j\j(jopsis zone on Mount Stephen, aliove 
 Field, British Columbia. 
 
 NiSUSIA FESTINATA TRANSVERSA (AValcott) (j). 729). 
 
 Figures 4 and 4a. The two specimens on which the species was founded. I'. S. Nat. Mus. Cat. Nos. 15361a and 
 15361b, respectively. Specimens figured by Walcott [18S6l>. PI. VII. figs. 5 and 5a] as Orlhisina 
 traitsrrrsn. Figure 4 represents the type specimen. 
 4b. Interior of a ventral valve. V. S. Nat. Mus. Cat. No. 52293a. 
 
 The specimens represenled are all from Locality 25. Lower Cambrian sandstone just above Parker's quarry, 
 near Georgia, Franklin County, Vermont. 
 336 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH U PL. C 
 
 PRANCES WIESER DEL. 
 
 HCLIOTVPE CO BOSTOM 
 
PLATE CI. 
 
 62667°— VOL 51, pt 2—12 22 337 
 
PLATE CI. 
 
 a. Cardinal area. d'. Cast of iimbonal cavity. 
 
 b. Dental sockets. dl. Delthyrium. 
 
 c. Crura. e. Adductor scars. 
 
 d. Deltidiuin. j. Cardinal process. 
 
 NisusiA (Jamesella) perpasta (Pompeckj) (p. 735). 
 
 Figures 1 and la. Exterior and side views of a strongly costate ventral valve from Locality 34Sk, Lower Cambrian 
 
 sandstones at Slapnicky Ml^n, near Skrej, Bohemia. U. S. Nat. Mus. Cat. No. 52302a. 
 lb and Ic. Casts of exterior of ventral valves associated with the specimen represented by figures 1 and la. 
 
 U. S. Nat. Mus. Cat. Nos. 52302b and 52302c, respectively. 
 Id, Id', and Id". Summit, back, and side \'iews of cast of exterior of ventral valve from Locality 345i, Lower 
 
 Cambrian conglomeratic sandstones of the Kamenni hurka, near Tejfovik, Bohemia. U. S. Nat. 
 
 Mus. Cat. No. 52301a. 
 le. Cast of a dorsal valve associated with the specimen represented by figures 1 and la. U. S. Nat. Mus. Cat. 
 
 No. 52302d. 
 If. Cast of a dorsal valve associated with the specimen represented by figure Id. V. S. Nat. Mus. Cat. No. 
 
 52301b. 
 Ig. Front view of cast of ventral valve from Locality 3451, see figure Id. Copied from Pompeckj [1896b, PI. 
 
 XV, fig. 16d]. 
 Ih. Cast of dorsal valve associated with the specimen represented by figures 1 and la. U. S. Nat. Mus. Cat. 
 
 No. 52302e. 
 
 NisusiA (Jamesella) perpasta subquadrata (Pompeckj) (p. 7.36). 
 
 Figure 2. Cast of ventral valve from Locality 3451, Lower Cambrian conglomeratic sandstones of the Kamenni hflrka, 
 
 near Tejrovik, Bohemia. U. S. Nat. Mus. Cat. No. 52304a. 
 2a. Cast of ventral valve from the locality represented by figure 2. Type specimen, copied from Pompeckj 
 
 [189Gb, PI. XV, fig. 19a]. 
 2b. Cast fit dorsal valve from the locality represented by figure 2. Copied from Pompeckj [1896b, PI. XV, 
 
 fig. 20a]. 
 
 NisusiA (Jamesella) perpasta macra (Pompeckj) (p. 736). 
 
 Figure 3. Cast of ventral valve doubtfully referred to this variety from Locality 3451, Lower Cambrian conglomeratic 
 sandstones of the Kamennd hurka, near Tejrovik, Bohemia. U. S. Nat. Mus. Cat. No. 52303a. 
 3a. Cast of dorsal valve from the locality represented by figure 3. Type specimen, copied from Pompeckj 
 [lS96b, PI. XV, fig. 14]. 
 
 NisusiA (Jamesella) kuthani (Pompeckj) (p. 732). 
 
 Figures 4 and 4'. Cast of exterior of ventral valve, with back view. U. S. Nat. Mus. Cat. No. 2G643a. 
 
 4a, 4a', and 4a". Summit, back, and side views of a cast of a ventral valve. U. S. Nat. Mus. Cat. No. 
 
 26643b. 
 4b. Cast of dorsal valve. U. S. Nat. Mus. Cat. No. 26643c. 
 
 The specimens represented are all from Locality 345i, Lower Cambrian conglomeratic sandstones of the Kamennd 
 hflrka, near Tejfovik, Bohemia. 
 
 NisusLv (Jamesella) erecta Walcott (p. 732). 
 
 Figures 5, -58, and 5b. Ventral, dorsal, and back views of the type specimen, which consists of the two valves united. 
 In figure 5a the tmibo has been restored; on figure 6 the ribs arc too much rounded. From Locality 
 313g, Middle Cambrian limestone at the south end of the Timpahute Range in the Groom mining dis- 
 trict, Nevada. V. S. Nat. Mus. Cat. No. 52299a. 
 338 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. CI 
 
 PflANCea W.ESER DEL. 
 
PLATE CI. 339 
 
 NisusiA (Jamesella) amii Walcott (p. 731). 
 
 Figures 6, Ca, and 6b. Top, side, and back views of the type epecimen, a ventral valve from Locality 66a, Lower 
 Cambrian limestone bowlder in Sillery conglomerate on the south shore of the St. LawTcnce, 4 miles 
 (C.4 km.) below Quebec, Canada. U. S. Nat. Mus. Cat. No. 52296. 
 
 Orusia? eurekensis (Walcott) (p. 765). 
 
 Figures 7, 7', and 7". Top, posterior, and side views of part of mold of the interior of a ventral valve, the type 
 specimen. U. S. Nat. Mus. Cat. No. 24596a. 
 7a, 7a', and 7a". Top, posterior, and side views of a mold of the interior of a dorsal valve. U. S. Nat. Mus. 
 Cat. No. 24596b. 
 
 The specimens represented are both from Locality 65b, Middle Cambrian, top of Eldorado limestone on west side 
 of Secret Canyon, Eureka district, Nevada. The figures (7 and 7a) are redrawn from the specimens illustrated by 
 Walcott [1884b, PI. IX, figs. 8a and 8, respectively]. 
 
 BiLLINGSELLA DICE Walcott (p. 754). 
 
 Figures 8, 8', and 8a. Casts of the interior of two ventral valves, with side view. U. S. Nat. Mus. Cat. Nos. 52248a 
 and 52248b, respectively. Figure 8 represents the type specimen. 
 8b. Partial posterior view of the matrix of a distorted ventral valve. U. S. Nat. Mus. Cat. No. 52248c. 
 8c. Matrix of a distorted dorsal valve. U. S. Nat. Mus. Cat. No. 52248d. 
 8d. Cast of the interior of a distorted dorsal valve. V. S. Nat. Mtis. Cat. No. 52248e. 
 
 The specimens represented are all from. Locality 319f, Lower Ordovician drift bowlder of sandstone found near 
 St. Albans, Vermont. 
 
 NisusiA (Jamesella) argenta Walcott (p. 731). 
 
 Figure 9. Top and side view of the type specimen, a ventral valve from Locality Ip, limestones of No. 2 of the Silver 
 Peak group, about 2.5 miles south of Barrel Spring, Silver Peak quadrangle, Nevada. U. S. Nat. Mus. 
 Cat. No. 52297a. 
 
 9'. Posterior view of another ventral valve. The specimen from which this was drawn can not be located. 
 
 9a and 9a''. Top and side views of a ventral valve from Locality Im, limestones of No. 2 of the Silver Peak 
 group, about 2.5 miles south of Barrel Spring, Silver Peak quadrangle, Nevada. 
 
 9b and 9b'. Top and side views of a dorsal valve. U. S. Nat. Mus. Cat. No. 52298b. 
 
 NistisLA (Jamesella) utahensis Walcott (j). 737). 
 
 Figures 10 and 10a. Top and side views of the type specimen, from Locality 7w, Middle Cambrian limestone in Rock 
 Canyon, in the Wasatch Mountains, east of Provo, Utah County, Utah. 
 
PLATE CII. 
 
 341 
 
PLATE CII. 
 
 a'. Anterior adductor scars. sp. Cast ofspondyllum. 
 
 a". Posterior adductor soirs. vs. Vascular sinus, 
 
 s. Median septum supporting spondylium. 
 
 Syntuophia bakabuensis (A. Winchell) (p. 799). 
 
 Figure 1. Cast of the interior of a ventral valve, showing the base of the median septum lliat f<upported the spondyl- 
 ium, the cast of which is clearly indicated. Locality 134a, L'pper Cambrian sandstone in quaiTy 
 1 mile (1.6 km.) southeast of the courthouse, Menouionie, Dunn County, Wisconsin. 
 
 la. Cast of the interior of a transverse ventral valve associated with the specimen represented by figure 1, 
 with posterior and side outline. U. S. Nat. Mus. Cat. No. 52473b. 
 
 llj. Top view and side outline of a cast of a ventral valve from Locality 83, Upper Cambrian sandstone near 
 Trempealeau, Trempealeau County, Wisconsin. U. S. Nat. Mus. Cat. No. 52472a. The median 
 sinus is very faintly impressed; see figures Ic and Id, where it is narrower and deeper. 
 
 Ic and Id. Top views and side outlines of casts of ventral valves showing variatiim in form and in the Ijreadth 
 and depth of the median sinus. From Locality 81o, Upper Cambrian sandstone below the Cliff 
 Hotise, Devils Lake, Sauk County, Wisconsin. U. S. Nat. Mus. Cat. No. 52474a and 52474b, 
 respectively. 
 
 le and Ig. Top views and side outlines of casts of the interior of dorsal valves, illustrating variation in form, 
 median fold, and cast of spondylium. They are associated with the specimen represented by figure 
 lb. U. S. Nat. Mus. Cat. Nos. 52472b and 52472c, respectively. 
 
 If. Top view and side outline of a cast of the interior of a dorsal valve associated with the specimen represented 
 by figure Ic. Compare the median fold and the cast of the spondylium of this specimen with those of 
 figures Ic and Ig. U. S. Nat. Mus. Cat. No. 52474c. 
 
 Syntrophia primokdialis (Wliitfield) (p. 803). 
 
 Figure 2. Cast of the interior of a ventral valve, showing cast of the spondylium, the supporting median septum and 
 
 large vascular sinuses. U. S. Nat. Mus. Cat. No. 52486a. 
 2a and 2b. Casts of the interior of ventral valves, illustrating variation in form. U. S. Nat. Mus. Cat. Nos. 
 
 52486b and 52486c, respectively. 
 2c and 2c'. Top and side views of cast of the interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52486d. 
 
 The specimens represented by figure| 2, 2a-c are from Locality 99, Upper Camlirian .sandstone at Minneiska, 
 Minnesota. 
 
 Figures 2d and 2e. Side and top views of the type specimen of the species, a dorsal valve from Locality 328k, Upper- 
 Cambrian, "St. Croix sandstone" at Roche ^ Cris Bluff, Adams County, Wisconsin. Copied from 
 Whitfield [1882, PI. X, figs. 1 and 2]. 
 
 Syntrophia primordialis argia AValcott (p. 804). 
 
 Figure 3. Cast of the interior of a ventral valve, the type specimen, from Lo<aIity 97, Upper Cambrian sandstone at 
 Reads Landing, foot of Lake Pepin, Wabasha County, Minnesota. U. S. Nat. Mus. Cat. No. 52492a. 
 
 Syntrophia nundina Walcott (p. 802). 
 
 Figures 4 and 4'. Exterior and side views of a ventral valve from Locality 204, Lower Ordovician Pogonip limestone 
 
 on eastern slope of ridge east of Hamburg Ridge, Eureka district, Nevada. U. S. Nat. Mus. Cat. No. 
 
 17281a. Type specimen figured by Walcott [1884b, PI. XI, fig. 7] as Triplma calci/era. 
 4a. Exterior of a dorsal valve from Locality 203, Lower Ordovician Pogonip limestone on ridge extending 
 
 southwest from Wood Cone, Eureka district, Nevada. U. S. Nat. Mus. Cat. No. 17279a. Specimen 
 
 figun-d by Walcott [1884b, PL XI, fig. 8] as Triplegia calcifcra. 
 4b. Partly exfoliated ventral valve, in which the beak is either broken or partly worn away. Associated 
 
 with the specimen represented by figtire 4a. I^. S. Nat. Mus. Cat. No. 17279b. 
 4c. Castof the interior of a ventral valve, having an unusually deep and strongly marked median sinus. Ixical- 
 
 ity 201a, Lower Ordovician Pogonip limestone on ea.st slope of ridge east of Hamburg Ridge, Eureka 
 
 district, Nevada. U. S. Nat. Mus. Cat. No. 17280a. 
 4d. Partly exfoliated dorsal valve, showing the cast of the spondylium and muscle scars. U. S. Nat. Mus. 
 
 Cat. No. 17491a. This specimen is doubtfully referred to this species. It is from Locality 329a. 
 
 Upper Cambrian limestone on I'te Peak, in the \\'asatch Mountains, east of Cache Valley, Cache 
 
 County, Utah. 
 342 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH L! PL. CD 
 
 FRANCES WIESER DEc. 
 
 HCLIOTYPE CO eOSTOM 
 
PLATE CII. 343 
 
 HUENELLA BILLINGSI (Walcott) (p. 806). 
 
 Figure 5. Casts of two ventral valves distorted by movement of the matrix in wliich they were embedded. U. S. Nat. 
 
 Mus. Cat. Nos. 52475a and 52475b, respectively. 
 5a. Exterior of a ventral valve, the type specimen, showing the character of the plications and median sinus. 
 
 U. S. Nat. Mus. Cat. No. 52475c. 
 5b. Exterior of dorsal valve, in the same layer of limestone willi specimen represented l)y ligure 5a. U. S. 
 
 Nat. Mus. Cat. No. 52475d. 
 5c. Exterior of dorsal valve. U. S. Nat. Mus. Cat. No. 52475e. 
 
 The specimens represented are all from Locality 28a, Middle ? Camlirian, ''St. Albans formation'" 1 mile (1.6 km.) 
 east of Parker's quarry, near Georgia, Franklin County, Vermont. 
 
 Syntrophia lateralis (Wliitfield) (p. 802). 
 
 [Text fig. 11, p. 299.] 
 
 Figure 6. Partly exfoliated, transverse ventral valve and side outline. U. S. Nat. Mus. Cat. No. 33447a. 
 
 6a. Partly exfoliated, subquadrate ventral valve and side outline. U. S. Nat. Mus. Cat. No. 33447b. 
 
 6b. Exterior of a transverse dor.sal valve. U. S. Nat. Mus. Cat. No. 33447c. 
 
 6c. Small young dorsal valve with only a trace of the median fold. U. S. Nat. Mus. Cat. No. 33447d. 
 
 6d. Oast of interior of dorsal valve, showing sides of spondylium, adductor scars, and vascular sinuses. U. S. 
 Nat. Mus. Cat. No. 33447e. 
 
 6e. Posterior \'iew of the two valves. U. S. Nat. Mus. Cat. No. 33447f. 
 
 6f. Portion of the interior of the ventral valve, showing the complete spondylium and the division of its sur- 
 face into median (adductor) and lateral (diductor) muscular areas. X 3. Copied from Hall and 
 Clarke [1893b, PI. LXII, fig. 9]. 
 
 6g. Oblique view of the specimen represented in figure 6f, showing the elevation of the spondylium and the 
 length of its supporting median septum. Copied from Hall and Clarke [1893b, PI. LXII. fig. 10]. 
 
 The specimens represented are all from Locality 227, Ordoviciau limestone near Fort Cassin, Addison County, 
 Vermont. 
 
PLATE cm. 
 
 345 
 
PLATE cm. 
 
 a'. Anterior adductor impressions. sp. Spondyliiim. 
 
 a". Posterior adductor impressions. s. Median .sei)( urn. 
 
 r. Diductor scar. vs. Vascular sinus. 
 
 HUENELLA TEXANA (Walcott) (}). 808). 
 
 Figure 1. Strongly costate ventral valve, the type specimen. U. S. Nat. Mus. Cat. No. 62494a. 
 
 la. Ventral valve with well-defined coatse in the mesial sinus, and nearly smooth cardinal .slopes. U. S. Nat. 
 
 Mus. Cat. No. 52494b. 
 lb. Ventral valve in which there are only slight traces of the radiating costse in the mesial sinu.'i. U. S. Nat. 
 
 Mus. Cat. No. 52494c. 
 Ic. Ventral valve without radiating costae, with back outline. U. S. Nat. Mus. Cat. No. 52494d. 
 Id. Ventral valve, with side outline, from Locality 71, Upper Cambrian limestone in Cold Creek Canyon, 
 
 Bin-net County, Texas. U. S. Nat. Mus. Cat. No. 52495a. 
 le. Dorsal valve, with strong costse on the median fold and cardinal slopes. U. S. Nat. Mus. Cat. No. 52494e. 
 If. Dorsal valve, with fine radiating costs. U. S. Nat. Mus. Cat. No. 52494f. 
 Ig. Dorsal valve, having median fold with well-marked costae and smooth cardinal -slopes, with back outline 
 
 of the same. U. S. Nat. Mus. Cat. No. 52494g. 
 Ih. Oblique section of spondylium of ventral valve a short distance from the apex. V. S. Nat. Mus. Cat. 
 
 No. 52494h. 
 li. Section of dorsal valve cutting across the spondylium. U. S. Nat. Mus. Cat. No. 524941. 
 
 With the exception of figiu-e Id, all the specimens represented arc from Locality 68. Upper Cambrian limestone, 
 in Packsaddle Mountain, Llano County, Texas. 
 
 HUENELLA ABNORMIS (Walcott) (p. 805). 
 [Text fig. 13, p. 299.1 
 
 Figure 2. Ventral valve with .strong radiating costse. U. S. Nat. Mus. Cat. No. 52462a. 
 
 2a and 2a'. Exterior and side views of ventral valve, the type specimen, with radiating costae in the mesial 
 
 sinus. U. S. Nat. Mus. Cat. No. 52462b. 
 2b. Cast of interior of ventral valve, showing cast of spondylium, main vascular canals, and muscle scars. 
 
 U. S. Nat. Mus. Cat. No. 52462c. 
 2c. Dorsal valve with prominent median fold, from Locality 158, L^pper Cambrian limestone north of East 
 
 Gallatin River, near Hillsdale, Threeforks quadrangle (U. S. Geol. Survey), Gallatin County, Mon- 
 tana. U. S. Nat. Mus. Cat. No. 52461a. 
 2d and 2d'. Top and side view of nearly smooth dorsal valve. U. S. Nat. Mus. Cat. No. 52462d. 
 2e. Dorsal valve with several plications on median fold. U. S. Nat. Mus. Cat. No. 52462e. 
 2f. Interior of dorsal valve showing muscle scars and vascular markings. U. S. Nat. Mus. Cat. No. 52462f. 
 2g. Posterior view of a ventral valve showing area. U. S. Nat. Mus. Cat. No. o2462g. 
 2h. Partial cast of interior of dorsal valve. U. S. Nat. Mus. Cat. No. 524G2h. 
 2i. Interior of a dorsal valve in which the muscle scars and spondylium (cruralium) have been more or le.ss 
 
 eroded. U. S. Nat. Mus. Cat. No. 524621. 
 2j. Cast of the interior of a dorsal valve, showing strong muscle scars and radiating costse on the mesial fold. 
 
 This specimen is associated with the shell represented by figure 2c. L'. S. Nat. Mus. Cat. No. 52461b. 
 2k. Cast of the interior of a dorsal valve, .showing radiating ^'ascular canals at the top of the cast of four strong 
 
 costae. ThLs specimen is a.ssociated with the shell represented by figure 2c. L'. S. Nat. Mus. Cat. 
 
 No. 52461c. 
 21 and 2m. Sections of ventral and dorsal valves cut across the imibo to show sections of the spondylium in 
 
 each valve. U. S. Nat. Mus. Cat. Nos. 52462J and 52462k, respectively. 
 
 With the exception of figures 2c, 2j, and 2k, the specimens rei>resented by figures 2. 2a-in are from Locality 4j, 
 Middle Cambrian limestone at the head of Deep Creek, Canyon quadrangle (V . S. Geol. Survey), Yellowstone 
 National Park, Wyoming. 
 346 
 
MONOGRAPH LI PL. CHI 
 
 U. S. GEOLOGICAL SURVEY 
 
 FRANCES V.tESER Dfl. 
 
 HtLlOTVPE CO BOSTON 
 
PLATE cm. 347 
 
 Syntrophia alata Walcott (p. 799). 
 
 Figures 3, 3', and 3". Cast of the interior of a ventral valve, with side and back views. U. S. Nat. Mus. Cat. 
 No. 52466a. 
 3a. Exterior of ventral valve, the type specimen. U. S. Nat. Mu.s. Cat. No. 52466b. 
 
 3b and 3c. Casts of interior of ventral valves. U. S. Nat. Mus. Cat. Nos. 52466c and 52466d, respectively. 
 3d. Partial cast of the interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 52466f. 
 
 The specimens represented by figures 3, 3a-d are all from Locality 69. Tapper Cambrian limestone near Honey 
 Creek, Burnet County, Texas. 
 
 Syntrophia rotundata Walcott (]>. 804). 
 
 Figures 4, 4'; 4a; and 4b, 4b'. Top and side views of three dorsal valves varying in form and in strength of median 
 fold. U. S. Nat. Mus. Cat. Nos. 52493a, 52493b, and 52493c, respectively. 
 
 4a'. View of area and hinge line of ventral valve. U. S. Nat. Mus. Cat. No. 52493h. 
 
 4c and 4c'. Top and side views of ventral valve, the type specimen. V. S. Nat. Mus. Cat. No. 52493d. 
 Another specimen (Cat. No. 52493g) was used to restore certain portions of this figure. 
 
 4d. Section across the umbo of a ventral valve, showing outline of section of spondylium. IT. S. Nat. Mus. 
 Cat. No. 52493e. 
 
 4e. Section of shell and spondylium of dorsal valve. U. S. Nat. Mus. Cat. No. 52493f. 
 
 The specimens represented by figures 4, 4a-e are all from Locality 14k. LTpper Cambrian limestone on Wolf 
 Creek, 15 miles (24.2 km.) west-southwest of Sheridan, Bighorn Mountains, Wyoming. 
 
PLATE CIV. 
 
 349 
 
PLATE CIV. 
 
 cl. Area of attachment of posterior muscles. nc. Umbonal cavity, 
 
 h. Central scars. vs. Main vascular sinuses, 
 
 sp. Cast of spondyliuni. 
 
 Syntrophia calcifera (Billings) ({>. 800). 
 
 Figure 1. Ventral valve.-probably the one represented by figure Ic. Copied from Billings [1861a, fig. 3a, p. 319]. 
 
 la. Dorsal valve, possibly the one represented by figure le. Copied from Billings [1861a, fig. 3b, p. 319]. 
 
 lb. Cast of a ventral valve showing spondylium. Copied from Billings [1861a, fig. 3c, p. 319]. 
 
 Ic and Ic'. Top and side views of ventral valve, from Locality 392j, Lower Ordovician limestone at Point 
 Levis, Province of Quebec, Canada. Geol. Survey Canada. In all probability this is the specimen 
 used by Billings in drawing his figure 3a [1861a, p. 319]. It may be taken as the type. 
 
 Id. Ventral valve with gently rounded shallow sinus, with a large projection to fit in the fold of the dorsal valve. 
 It is associated with the specimen represented by figure Ic. Gcol. Survey Canada. 
 
 le and le'. Top and side views 6i a dorsal valve from Locality 3921, Lower Ordo\'ician limestones at 
 Phillipsburg, Province of Quebec. Geol. Survey Canada. The specimen represented by figure le is 
 possibly the one used by Billings in drawing his figure 3b [1861a, p. 319]. 
 
 If. Ventral valve with side outline. U. S. Nat. Mus. Cat. No. 52476a. 
 
 Ig and Ih. Top and side \-iew of a ventral valve. U. S. Nat. Mus. Cat. No. 52476b. 
 
 li. A smooth dorsal valve, doubtfully referred to this species. U. S. Nat. Mus. Cat. No. 52476c. 
 
 The specimens represented by figures If-i are from Locality 392], Lower Ordovician limestones at Point Levis, 
 Province of Quebec, Canada. 
 
 Clarkella montanensis (Walcott) (]>. 810). 
 
 Figures 2 and 2'. Top and back view of a broken ventral valve. U. S. Nat. Mus. Cat. No. 11587a. 
 
 2a and 2a'. Top and side view of a rhomboidal dor.sal valve, the type specimen. U. S. Nat. Mus. Cat. No. 
 
 11587b. 
 2b. Transverse dorsal valve. U. S. Nat. Mus. Cat. No. 11587c. 
 2c and 2d. Sections across the umbo of two ventral valves, showing sections of the septa supporting the 
 
 spondylium. U. S. Nat. Mus. Cat. Nos. 11587d and 11587e, respectively. 
 
 The specimens represented are all from Locality 302j, Ordovician limestone east of West Gallatin (Gallatin) 
 River, above Gallatin, Gallatin County, Montana. 
 
 Huenella orientalis (Walcott) (p. 808). 
 
 Figure 3. Top and side views of a ventral valve, the type specimen. U. S. Nat. Mus. Cat. No. 52564a. 
 3a. Top and side views of an exfoliated dorsal valve. LT. S. Nat. Mus. Cat. No. 52564b. 
 3b. Partly exfoliated dorsal valve. U. S. Nat. Mus. Cat. No. 52564c. 
 
 The specimens represented are all from Locality C64, Upper Cambrian limestone 2.7 miles (4.4 km.) southwest of 
 
 Yenchuang, Sintai district, Shantung, China. 
 
 / 
 
 Syntrophia ortiiia Walcott (p. 803). 
 
 Figure 4. Ventral valve, the type (specimen, from Locality C56, Upper Cambrian Chaumitien limestone at Pagoda 
 
 Hill, 1 mile (1.6 km.) west of Tsinan, Shantung, China. U. S. Nat. Mus. Cat. No. 52562a. 
 4a and 4a'. Exterior of ventral valve, with side outline, from Locality C64, ri)per Cambrian limestone 2.7 miles 
 
 (4.4 km.) southwest of Yenchuang, Sintai district. Shantung, China. U. S. Nat. Mus. Cat. No. 
 
 52563a. 
 4b and 4b'. Top and side views of a dorsal valve from Locality C54, Upper Cambrian Chaumitien limestone 
 
 0.66 mile (1.1 km.) west of Tsinan, Shantung, China. U. S. Nat. Mus. Cat. No. 52561a. 
 
 SWANTONIA ANTIQUATA (BilUngs) (p. 797). 
 
 Figures 5, 5a, and 5b. Top, side, and back views of the cast of a ventral valve from Locality 319e, Lower Cambrian 
 sandy shales about 2 miles (3.2 km.) east of Swanton, Franklin County, Vermont. V. S. Nat. Mus. 
 Cat. No. 15363a. This specimen was figured by Walcott [llSSOb, PI. VII, fig. 8] as Camarella aniiquala. 
 
 350 
 
U. S. GEOLOGICAL SURVEY 
 
 MONOGRAPH LI PL. CIV 
 
 ..^:M^=^ 
 
 7a' 
 
 FRANCES WIESER OEL. 
 
 LIOTVPE CO OOSTOI. 
 
PLATE CIV. 351 
 
 SWANTONIA WEEKSI Walcott (p. 797). 
 
 Figure 6. Top view of an imperfect ventral valve, the type specimen, from Locality Iv, Lower Cambrian shales of 
 No. 3 of the Silver Peak group, 3 miles north of Valcalda Spring and 4 miles northwest of the Drink- 
 water mine, Esmeralda County, Nevada. U. S. Nat. Mus. Cat. No. 52500a. 
 
 QuEBECiA CIRCE (Billings) (p. 610). 
 
 Figure 7. Cast of interior of ventral valve, showing outline of main vascular sinu.ses and cardinal muscle scars. U. S. 
 
 Nat. Mus. Cat. No. 14892a. 
 7a and 7a'. Back and side views of specimen represented by figure 7. U. S. Nat. Mus. Cat. No. 14892a. 
 7b. Back view of the cast of a ventral valve, in which the cardinal scars are large and strongly defined. The 
 
 specimen from which this figure was drawn can not be located. 
 7c. Cast of the interior of a dorsal valve. IT. S. Nat. Mus. Cat. No. 14892c. 
 7d. Artificial cast of the interior of a dorsal valve. The original specimen can not be located. U. S. Nat. 
 
 Mus. Cat. No. 14892f. 
 7e. Artificial cast taken from the artificial cast shown by figure 7d. U. S. Nat. Mus. Cat. No. 14892e. 
 
 Specimen figured by Walcott [1886b, PI. X, fig. 3a]. 
 7f. Cast of the interior of a dorsal valve. U. S. Nat. Mus. Cat. No. 14892b. 
 7g. Cast of the interior of a dorsal valve which is old and thick .shelled. U. S. Nat. Mus. Cat. No. 14892d. 
 
 The specimens represented are all from Locality 3191, Lower Cambrian limestone bowlders in conglomerate at 
 Trois Pistoles, on St. Lawrence River below Quebec, Canada. 
 
INDEX TO PART 11, 
 
 Note.— This index includes also reference to species figured in Part I (text figures), and all page references are to that part. In order to make 
 the figured species easily accessible to one not familiar with the numerous changes in the generic references the entries are arranged alphabetically 
 by genera, subgenera, species, and varieties. Roman numerals refer to plates, arable numerals to the figures on the plates. The index to Part I 
 includes the plate and figure reference of each of the type specimens figured in the monograph. 
 
 abnormis [HuenellaJ, (Walcott ) CIII: 2, 2a-m; 
 
 Text fig. 13, p. 299. 
 
 acadicus [Oboius], Walcott XI; 5. 
 
 (Acritis) antiquissunus [Oboius], (Eichwald) XIII: 3; 
 
 XV:2, 2a-d. 
 
 (Acritis?) rugatus [Oboius], Walcott XXII: 2 and 3. 
 
 Acrothele artemis Walcott Text fig. 54, p. 634. 
 
 avia Matthew LXI: 7, 7a-b: 
 
 LXII:l,la-k. 
 
 avia puteis Matthew Not figured. 
 
 bellapunctata Walcott L\'II: 3, 3a-b. 
 
 bellula Walcott LVIII: 5, 5a-h. 
 
 bergeroni Walcott LVIII: 6, 6a-c. 
 
 bohemiea ( Barrande) LVII; 1, la-d. 
 
 borgholmensis Walcott LXIII: 2, 2a-b. 
 
 ceratopygarum (Brogger) LXIII: 1, la-c. 
 
 colleni Walcott LXIII: 6, 6a-b; 
 
 Text figs. 55A-E, 
 p. 641. 
 
 coriacea Linnarsson LVI: 1 , la-i. 
 
 decipiens Walcott LVIII: 3,3a-d. 
 
 diehotoma Walcott LX: 2. 
 
 gamagei (Hobbs) LX: 5, 5a-c. 
 
 intermedia Linnarsson LVI: 3, 3a-d. 
 
 levisensis Walcott LXXXI: 12, 12a-b. 
 
 maculata (Salter) LVII: 2, 2a-b; 
 
 LVIII: 2. 
 
 matthewl (Hartt) LXI: 1, la-g. 
 
 matthewieryx Walcott LXI: 2. 
 
 matthewi lata Matthew LXI: 3. 
 
 matthewi multicostata Matthew LXI: 5, 5a-c. 
 
 ? minuta Walcott .' LXIII; 3. 
 
 nitida (Ford) LVIII: 4, 4a. 
 
 panderi Walcott LIX: S, 5a-c. 
 
 pretiosa ( Billings) LVIII: 1 , la-g. 
 
 prima (Matthew) LXI:6, Oa-b; 
 
 LXII; 2. 
 
 prima costata (Matthew) LXI: 4, 4a-d. 
 
 primiBva (de Verneuil and Barrande) LVII: 6. 
 
 proles Matthew LXII: 3, 3a-e; 4, 4a, 
 
 quadrilineata Pompeckj LVII: 5. 
 
 rara Walcott LXIII: 4, 4a. 
 
 spurri Walcott LX: 3. 3a-c. 
 
 subsidua (White) LX: l,la-o; 8. 
 
 subsiduahera Walcott LX: 9. 
 
 subsidua Iwvis Walcott Not figured. 
 
 turaeri Walcott LX: 7, Ta. 
 
 villahoimensis Delgado Not figured. 
 
 woodworthi Walcott LX: G. 
 
 yorkensis Walcott LIX:4, 4a-b. 
 
 sp. undt. Moberg Not figured. 
 
 sp. undt. Walcott LXIII: 5. 
 
 Acrothele (Redlichella) granulata (Linnarsson) LVI: 2,2a-n. 
 
 Acrothyra minor Walcott LXXVI: 4, 4a-b; 
 
 Text fig. 59, p. 717. 
 
 proa via (Matthew) LXX V: 3; 
 
 LXXVI:3,3a-u. 
 
 sera (Matthew) LXXX: 4,4a-c; 5, 
 
 5a-d; 6,6a-i; 7, 
 7a-b; 8?. 
 
 signata Matthew LXXX : 1 , la-d . 
 
 signata orta Matthew LXXX: 3. 3a-b. 
 
 signata prima Matthew LXXX: 2, 2a-b. 
 
 62667°— VOL 51, pt 2—12- 
 
 -23 
 
 Acrotreta argenta Walcott LXVII: 5, oa-g. 
 
 attenuata Meek LXPV: 1, la-o; 
 
 LXXIX: 6,6a. 
 
 attenuata var. Walcott LXV: 2. 
 
 babel Barrande LXXVII: 6, 6a-b. 
 
 baileyi Matthew LXXVII: 2, 2a-d. 
 
 bellatula Walcott LXXVIII: 4, 4a-d. 
 
 belti (Davidson) LXXVII: 8, 8a. 
 
 bisecta Matthew LXVI: 7,7a~e. 
 
 ?? cancellata Walcott LXXIX: 5, Sa. 
 
 carinata (Scgerberg MS.) Moberg and Segcr- 
 
 herg Text figs. 06A-D, 
 
 p. 689. 
 circularis Moberg and Scgerberg Text figs. 57A-C, 
 
 p. 680. 
 
 claytoni Walcott LXXIV: 3, 3a-b. 
 
 concentrica Walcott LXXVII: 1, la-b. 
 
 conula Walcott LXXV: 2. 2a-b. 
 
 convcxa Walcott LXVI: 6, 6a-c. 
 
 curvata Walcott LX VIII: 1 , la-n. 
 
 definita Walcott LXIV: 2,2a-g, 3, 
 
 3a-b, 
 
 depressa (Walcott) LXVI: 8, 8a-c. 
 
 eggegrundensis Wunan LXX: 2a-d. 
 
 emmonsi Walcott LXV: 6. 
 
 germna Billings LXVI: 1, la-b. 
 
 gemmula Matthew LXVI: 3, 3a-c; 
 
 LXXVII: 5,5a-f. 
 
 gracia Walcott LXVI: 5, 5a-d. 
 
 idahoensis Walcott LXV: 1, la-i; 
 
 LXVIII: 2,2a-g. 
 
 cf. idahoensis Walcott Not figured. 
 
 idahoensis alta Walcott LXV; 4,4a-b. 
 
 idahoensis sulcata Walcott LXV; 5. 
 
 inchoans (Barrande) XV: 7, 7a. 
 
 inflata (Matthew) LXXVI: l,la-k; 2, 
 
 2a. 
 
 loitorgai Walcott LXV: 3, 3a-e, g-k; 
 
 Text fig. 58, p. 692. 
 
 lisani Walcott LXVIII: 3,3a-c. 
 
 marjumensis Walcott LXXVIII: 2, 2a^d. 
 
 microscopica (Shumard) LXVII: I, la-h, lo; 
 
 2, 2a-d. 
 
 microscopica missouriensis Walcott LXVII: 4, 4a-b. 
 
 microscopica tetonensis Walcott LXVII: 3, 3a-d. 
 
 7 minima ( Barrande) LXXVII: 7, 7a. 
 
 mlsera ( Billings) LXXII: 2, 2a-l. 
 
 neboensis Walcott LXXVII: 9, 9a-b. 
 
 nicholsoni Davidson LXXIII: 1, la-k;6, 
 
 6a-b. 
 
 nox Walcott LXXVII; 10. 
 
 oelandica Westergird Not figured. 
 
 ophirensis Walcott LXXIV: 1, la-p. 
 
 ophirensis descendens Walcott LXXVIII: 1, la-c. 
 
 opliirensis rugosa Walcott LXXIV; 2, 2a-e. 
 
 ovalis Walcott LXVI: 2, 2a-b. 
 
 pacifica Walcott LXIX: 6, 6a-e. 
 
 pari-ula (Wallerius) LXXVII; 4, 4a. 
 
 prim^eva Walcott LXIX: 1, la-f. 
 
 pyxidicula White LXIX: 2, 2a-f; 3, 
 
 3a-f. 
 
 rudis Walcott LXV; 3f; 
 
 LXXV: 1. 
 
 353 
 
354 
 
 CAMBKIAN BRACHIOPODA. 
 
 Aerotrcta sabrinae (Callaway) LXXIII: 5, 5a-d. 
 
 sagittalis (Salter) LXXI: 2, 2a-h; 3, 
 
 3a-j. 
 
 cf. sagittalis Not figured. 
 
 sagittalis magna (Matthew) LXVI: 4, 4a-f. 
 
 sagittalis taconica ( Walcott ) LXXI: 1, la-o. 
 
 sagittalis transversa (Uartt) LXXII: 1, la-k. 
 
 sctimalenseei Walcott LXX : 1, la-s. 
 
 seebachi Walcott LXX VII: 3, 3a. 
 
 shantungensis Walcott LXIX: 5, 5a-e. 
 
 signalis Walcott LXIX: 4. 
 
 socialis von Seebach LXXIII: 3, 3a--c; 4, 
 
 4a-e. 
 
 spinosa Walcott LXXIX: 4, 4a-g. 
 
 subconica Kutorga LXXIII: 2, 2a^i. 
 
 ulrichi Walcott LXX VIII: 3. 
 
 uplandica Wiman LXX: 3, 3a-c. 
 
 uplandica limoensis (Wiraan) LXX: 4, 4a-c. 
 
 sp. undt. Walcott Not figured. . 
 
 sp. undt. Wcstergard Not figured. 
 
 acuminata [Lingulella (Lingulepis)], (Conrad) XXXIV: 3, 3a-c; 
 
 XL: 1, la-s; 
 XLI: 1, la-n; 
 XLII: 1, la-o. 
 acuminata meeki [Lingulella (Lingulepis)), (Wal- 
 cott) XLI: 2,2a. 
 
 acuminata sequens [Lingulella (Lingulepis)), Wal- 
 cott Te.xt figs. 46.\-B, 
 
 p. 551. 
 
 acuminatus [Obolus (Scbmidtia)], Mickwitz XIV: 2, 2a-c. 
 
 acutangula [Lingulella), (Roemer) XVII: 1, la-o. 
 
 advenus[Obolus?), Barrandc XII: 5, 5a-b. 
 
 affinis [OboUis (Lingulobolu.s)), (Billings) XVI: 1, la-e. 
 
 agnostorum [Lingulella], (Wallerius) XXX: 15. 
 
 agreste [Eoorthis], (Walcott) LXXXIX: 6, 6a. 
 
 alabamaensis [Micromitra] , (Walcott) II: 5, 5a-c. 
 
 Wandensis [Obolus (Westonia)), Walcott XLVIII: 6, 6a. 
 
 alata [Syntrophia), Walcott CIII: 3, 3a-d. 
 
 alberta [.\isusia), (Walcott) C: 3, 3a-d. 
 
 alta [.\crotreta idahoensis), Walcott LXV: 4, 4a-b. 
 
 ambigua [Elkania), (Walcott) LI: 2, 2a-c. 
 
 amii [Nisusia (Jamesella)), Walcott CI: 6, 6a-b. 
 
 ampla [Lingulella), (Owen) XXVIII: 1, la-j. 
 
 anatina [Lingula], Bruguidre Text figs. 34C-D, 
 
 p. 374. 
 
 anceps [Obolus), Walcott X: 3, 3a-f. 
 
 ancillus [Obolus ?), (Barrandc) XII: 2. 
 
 anomala [ Wimanella ?), (Walcott) LXXXVII: 1, la-e. 
 
 antiquata [Swantonia), (Billings) CIV: 5, 5a-b. 
 
 antiquissimus [Obolus (.\critis)), (Eichwald) XIII: 3; 
 
 XV: 2.2a-d. 
 
 apollinis [Obolus], Eichwald VII: 1-8, 10-17; 
 
 XIV: 6, 6a; 
 Text figs. 4 and 15, 
 p. 299. 
 
 apollinis ingricus [Obolus], Eichwald Not figured. 
 
 apollinis maxim us [Obolus], Mickwitz VII: 9; 
 
 XIV: 7. 7a. 
 
 apollinis quenstedti [Obolus], (Mickwitz) Text figs.34A-B,p. 
 
 374. 
 
 appalacliia [Billmgsella?], Walcott LXXXVII: 2, 2a-b. 
 
 appalachia [DiccUomus], Walcott LIU: 4, 4a-g. 
 
 argenta [ Acrotreta], Walcott LX VII: 5, 5a-g. 
 
 argenta [Nisusia (Jamesella)], Walcott CI: 9.9a-b. 
 
 argla [Syntrophia primordialis], Walcott CII: 3. 
 
 arguta [Lingulella], (Walcott) XXIV: 5. Sa-b. 
 
 artemis [ Acrothele], Walcott Text fig. 54, p. 634. 
 
 asiatica [Obolella], Walcott LV: 0. Oa. 
 
 atava [Lingulella], (Matthew) XXXV: 5. 5a-h. 
 
 atava [Eoorthis], (Matthew) XCV: 7, 7a-b. 
 
 atava insula; (Lingulella). (Matthew) XXXV: .s, Xa. 
 
 atlantica [Obolella], Walcott LV: la- < 
 
 Text fig. 51, p. 590. 
 
 atrMJOides [Orusia Icnticularis], (Matthew) XCVIII: 5. 
 
 attenuata [Acrotreta], Meek LXIV: l.la-o; 
 
 LXXIX: 6,6a. 
 
 attenuata var. [Acrotreta], Walcott LXV: 2. 
 
 auga [Lingulella], (Walcott) XXIV:6.6a-g. 
 
 aurora [Obolus (Westonia)], (Hall) XLVI: 1, la-h. 
 
 avia [Acrothele), Matthew LXI: 7,7a-b; 
 
 LXII: l.la-k. 
 
 aviaputeis [Acrothele), Matthew Not figured. 
 
 babel [.\crotreta], Barrandc LX X VII; 6, 6a-b. 
 
 baileyi (Acrotreta], Matthew L.KX VII: 2, 2a-d. 
 
 baltieus [obolus (Westonia)), Walcott XLVIII: 7, 7a-b. 
 
 barabuensis [.Syntrophia], (A. Winchell) CII: l,la-g. 
 
 ? barrandel(liots(ordial, Walcott LVII: 7,7a-b. 
 
 bavarica [Eoorthis), (Barrande) XCVII: 4. 
 
 bavaricus (Obolus?), ( Barrande) XV; 10, 10a. 
 
 bella (Lingulella), (Walcott) XIX: 2,2a-q; 
 
 X.XXVI: 4. 
 
 bella [Micromitra (Paterina)), (Billings) II: l,la-c. 
 
 bellapunctata (Acrothele), Walcott LVII: 3, 3a-b. 
 
 bellatula (.\crotrela), Walcott LXX VIII: 4,4a-d. 
 
 belli [Oljolus], (Billings) XXXVIII:3,3a-b. 
 
 bellula [Acrothele), Walcott LVIII: 5, 5a-h. 
 
 bellula (Lingulella), (Walcott) XIX: 1, la-e. 
 
 bellulus (Obolus (Fordinia)], (Walcott) LI:3,3a-f. 
 
 belli l-'Vcrotrcta), (Davidson) LXX\TI: 8, 8a. 
 
 bergeroni [.\crotheIe], Walcott LVIII: 6, 6a-c. 
 
 Bicia gemma ( Billings) L: 1, la-n. 
 
 whiteavesi Walcott L: 2. 2a-c. 
 
 Billmgsella? appalachia Walcott LXXXVII: 2, 2a-b. 
 
 bivia Walcott Text figs. 65A-C, p. 
 
 750. 
 
 coloradoensis (Shumard) LXXXV: 1, la-z; 
 
 Text figs. 5, p. 299, 
 and 06, p. 751 . 
 
 dice Walcott CI: 8. 8a-d. 
 
 exporrecta (Linnarsson) LXXXVIII:l.la-l. 
 
 exporrecta rugosicostata Walcott LXXXVIII:2,2a-c. 
 
 hicksi (.Salter MS.) (Davidson) XCVII: 7, 7a-b. 
 
 highlandensis (Walcott) .LXXXVII: 4,4a-c. 
 
 lindstromi (Linnarsson) LXXXVII: 6, 6a-f. 
 
 major Walcott LXXXVI; 1, la. 
 
 marion \\'alcott Text figs. 67A-B, 
 
 p. 758. 
 
 obscura Walcott LXX XVI: G. 
 
 orientalis (Whitfield) LXXXVI: 2, 2a-b. 
 
 plicatella Walcott LXXXVI: 3, 3a-n; 
 
 Text fig. 1, p. 299. 
 
 piimpeliyi Walcott XCVII: 8, 8a-c. 
 
 retrodexa (Matthew) XC: 1, la-h. 
 
 richthofeni Walcott LXXXIX: 1. 
 
 romingeri (Barrande) XC: 2, 2a-n. 
 
 salemensis (Walcott) LXXXVII: 3, .3a. 
 
 striata Walcott LXXXVI: 4, 4a-c. 
 
 whitfieldi (Walcott) LXXXVI: 5, 5a. 
 
 billingsi (Huenella), (Walcott) CII: S, 5a-c. 
 
 billingsi [Protorthisl, (Hartt) XCIX: 1, la-g. 
 
 billingsiana [Lingulella). (Whitcavcs) XXIX: 3,3a. 
 
 bisecta [.\crotreta), Matthew XLVI: 7, 7a-e. 
 
 bivia [Billingsella), Walcott Text figs. 65A-C, 
 
 p. 750. 
 
 blackweldcri [Obolus (Westonia)) Walcott XXXIX: 10, XOa-c. 
 
 bohemica [Acrothele], ( Barrande) LVII: 1, la-d. 
 
 borgholmensis [Acrothele], Walcott LXIII: 2, 2a-b. 
 
 bornemanni [Lingulella), (Walcott) XXX: 18, 18a-c. 
 
 Botsfordia? barrandei Walcott LVII: 7, 7a-b. 
 
 c:rlata (Hall) LIX:l,la-q;3,3a-b. 
 
 granulata (Redlieh) LVII: 4, 4a-r. 
 
 pulchra (Matthew) I.XII: 5, 5a-l. 
 
 bottnicns [Obolu.s (Westonia)], (Wiman) XLVIII: 4. 4a-c. 
 
 bretonensis [Obolus ( rahrobolus)), (Matthew) XXXII: 5, 5a-g. 
 
 bretonensis lens [Obolus (I'ahi'obolus)), (Matthew). Not figured. 
 
 (Brbggeria)salteri [Obolus], (lloll) XIII: 1, la-n; 
 
 XV: 4, 4a-il. 
 
 buchi [Keyserlingia], (de Verneoil) LXXXI: 4, 4a-e. 
 
 buttsi [Lingulella), Wahott XXIX: 4, 4a-b. 
 
 Ciclata [Botsfordia), (Hall) LIX: 1, la-q; 3, 
 
 3a-b. 
 
 calcilera [Syntrophia), (Billings) CIV: 1, la-i. 
 
 Cambria (Schuchertiua), Walcott LI: 6, Oa-m. 
 
 Cambria [Syntrophia], Walcott Text figs. 72A-D, 
 
 p. 800. 
 
 campbelli (Syntrophia), Walcott Text figs. 73A-F, 
 
 p. 801. 
 
 cancellata [Acrotreta??), Walcott LXXIX: 5, 5a. 
 
 cania [Lingulella), (Walcott) XXXA': 3, 3a-d. 
 
INDEX. 
 
 355 
 
 cariuata [Acrotreta], (Segerberg MS.) Moberg and 
 
 Segerberg Text figs. 56A-D, 
 
 p. 680. 
 
 cedens [Lingulella], (Barrande) XXX: 8. 
 
 celatus[ObolLi3(Scliiaidtia)], (Volborth) XIV: 1, la-c. 
 
 ceratopygaruin [Acrothele], (Brogger) LXIII; 1, la-c. 
 
 chinensLs[Obolusl, (Walcott) XXXIX: 7, 7a-b. 
 
 christianise [EoorthisJ, (Kjerulf) XCV: 1, la-h. 
 
 chromatica[OboIella), Billings LIV: 1, la-i. 
 
 chuarensis [Obolus (Westonia)], (Walcott) XXV: 2, 2a-«. 
 
 ciugulata[KutorginaJ, (Billings) V: 1, la-s; 
 
 Text flgs. 3 and 8, 
 
 p. 299, and 50A-C, 
 
 p. 581. 
 
 Circe [Quebecia], (Billings) CIV: 7, 7a-g. 
 
 circularis [.\crotreta], Moberg and Segerberg Text figs. 57 A-C^ 
 
 p. 680. 
 clarkei [Lingulella], Walcott Te.xt figs. 42A-D, 
 
 p. 486. 
 
 Clarkella montanensis ( W alcott) CIV: 2, 2a-d. 
 
 clarki [Dearbomia], Walcott LXXXII: 7, 7a-d. 
 
 claytoni [Aerotreta], Walcott LXXIV: 3, 3a-b. 
 
 coUeni [.\crotheleJ, Walcott LXIII: 6, 6a-b; 
 
 Text figs. 55A-E, p. 
 
 641. 
 collicia [Lingulella], (Matthew) XXXV: 1, la-I: 2, 
 
 2a-d. 
 
 coloradoensis [Billingsella], (Shumard) LXXXV: 1, la-z; 
 
 Text flgs. 5, p. 299, 
 
 and 66, p. 751 . 
 
 Columbiana [Philhedra], (Walcott) LXXXI: 10. 
 
 complexus [Obolus], Barrande XII: 3, 3a; S, 8a. 
 
 compta [Nisusia], (Tate) XCVII: 14. 
 
 concentrica [.\crotreta], Walcott LXX VII: 1, la-b. 
 
 concinna [Lingulella], Matthew XXXIII: 2, 2a~h: 
 
 XXXIV: 1, la-r. 
 
 contraria[Orbiculoidea], (Barrande) LXXXI: 9. 
 
 conula [Acrotreta], Walcott LXXV: 2, 2a-b. 
 
 convexa [Acrotreta], Walcott LX VI: 6, 6a-c. 
 
 convexa [Lingulella winona], (Walcott) XVIII: 4, 4a-d. 
 
 coriacea [Acrothele], Linnarsson LVI: 1, la-i. 
 
 corrugata [Finkelnburgia osceola], (Walcott) Not figured. 
 
 costata [Acrothele prima], (Matthew) LXI: 4, 4a-d. 
 
 crassa [Obolella], (Hall) LIV: 2, 2a-n; 
 
 Text fig. 14, p. 299. 
 
 crassa elongata [Obolella], Walcott LV: 5, 5a. 
 
 crassus [Obolus (Schmidtia)], Mickwitz XIV: 4, 4a-d. 
 
 crenistria [Micromitra (Paterina)], (Walcott) Ill: 4, 4a-b. 
 
 cuneola [Lingulella], (Whitfield) XXVII: 7, 7a-b. 
 
 Curticia elegantula Walcott I: 2, 2a-l. 
 
 curvata [.Vcrotreta], Walcott LX VIII: 1, Ian. 
 
 cyane [Obolus], (Billings) XX VII: 4, 4a-b. 
 
 Balmanella multisecta (Meek) Text fig. 9, p. 299. 
 
 parva (de Verneuil) Text fig. 10, p. 299. 
 
 subequata (Conrad) Text fig. 2. p. 299. 
 
 damesi [Lingulella], (Walcott) XXXIX: 8, 8a-c. 
 
 dartoni [Obolus (Westonia)l, Walcott Text figs. 40A-C, 
 
 p. 455. 
 
 daunus [EoorthLs], (Walcott) XCV: 2, 2a-c. 
 
 davidsoni [Lingulella], (Barrande) XXXII: 1, la-e. 
 
 davisi [Lingulella], (McCoy) XXX: 2, 2a: 
 
 XXXI: 6, Ga-h. 
 
 Dearbornia clarki Walcott LXXXII: 7, 7a-d. 
 
 decipiens [Acrothele], Walcott LVIII: 3, 3a-d. 
 
 decipiens [Obolus mcconnelli], Walcott XXIII: 4, 4a-b. 
 
 definita [-\crotreta], Walcott LXIV: 2, 2a-g; 3, 
 
 3a-b. 
 
 Delgadella lusitanica (Delgado) XXIX: 5, 5a-b. 
 
 delgadoi [Lingulella], Walcott XXIX: 6, 6a-c. 
 
 depressa [Acrotreta], (Walcott) XLVI: 8, 8a-c. 
 
 descendens [.Acrotreta ophirensis], Walcott LXX VIII: 1, la-c. 
 
 desiderata [Elkanial, (Billings) LI: 1, la-d. 
 
 desiderata [Lingulella], (Walcott) XX: 4, 4a-c; 5, 5a-j. 
 
 desmopleura [Eoorthis], (Meek) XCVI: 1, la-r. 
 
 desmopleura nympha[Eoorthis], Walcott XCVI: 2. 
 
 diablo [Eoorthis?], (Walcott) XCIII: 3. 
 
 dice [Billingsella], Walcott CI: S, 8a-d. 
 
 Dicellomus appalachia Walcott LIU: 4, 4a-g. 
 
 Dicellomus nanus (Meek and Ilayden) LIII: 1, la-1; 2,2a, 
 
 3, 3a-d. 
 
 parvus Walcott LXXXIX: ll,lla-d. 
 
 pectenoides ( Whitfieldj LII: 6, 6a-c; 
 
 Text flgs. 48A-B, 
 p. 575. 
 
 politus (Hall) LII: 1, la-k; 2, 2a-i; 
 
 3; 4, 4a; 5, 5a-b; 
 Text figs. 16A-B, 
 p.314.and49A-B, 
 p. 576. 
 
 prolificus Walcott 7 LXXXIX: lQ,10a-b. 
 
 sp. undt. Walcott LII: 7, 7a. 
 
 dichotoma[..Vcrothele], Walcott LX: 2. 
 
 Discinolepis granulata Waagen LXXXI: 3, 3a-b. 
 
 Discinopsis gulielmi (Matthew) LXXXII: 5. 5a-c. 
 
 7 sulcatus Walcott LXXXII: G. 
 
 discoideus [Obolus], (Hall and Whitfield) XVIII: G. 6a-d. 
 
 dolatus [ Obolus], (Sardeson) Text flgs. 35A-B, 
 
 p. 390. 
 
 doris [Eoorthis], (Walcott) XCVII: 13, 13a. 
 
 dubia [Lingulella], (Walcott) XXIV': 4,4a. 
 
 dubia [ Siphonotrela], Walcott LXXXI:7, 7a-b. 
 
 dugaldensis [Protorthis (Loperia)], Walcott XCIX: 5,5a-j. 
 
 edsoni [Rustella], Walcott I: l.la-e. 
 
 eggegrundensis [ Acrotreta], Wmian LXX: 2a-d. 
 
 eichwaldi [ Oliolus), Mickwitz Not figured. 
 
 elegans [Obolus], Mickwitz XV: 3. 
 
 elegantula [Curticia], Walcott I: 2, 2a-l. 
 
 elegantula [ Eostrophoniena], (Walcott) XCV: 6,Ga-b. 
 
 Elkania amhigua (Walcott) LI: 2. 2a-c. 
 
 desiderata (Billings) LI: 1, la-d. 
 
 Ida (Billings) XXX: 20, 20a; 
 
 LI: 4,4a-c. 
 
 ella [Obolus(Weston!a)], (Hall and Whitfield) XXXIIl: 3.3a-c; 
 
 XLVII: l,la-p. 
 
 ella onaquiensis [Obolus (Westonia)], Walcott XLIX: G.6a. 
 
 ellsi [Lingulella], (Walcott) XIX: 3,3a-c. 
 
 elongata [Obolella crassa], Walcott LV: 5, Sa. 
 
 elongatus [Obolus (Westonia)], Walcott LXIII; 8,8a-d. 
 
 emnionsi [.Vcrotreta], Walcott LXV: 6. 
 
 endlichi [Micromitra sculptilis], Walcott Text fig. 22, p. 342. 
 
 Eoorthis agreste (Walcott) LXXXIX: 6. 6a. 
 
 atava (Matthew) XCV: 7, 7a-b. 
 
 bavarica ( Barrande) XCVII: 4. 
 
 christianise (Kjerulf) XCV: 1, la-h. 
 
 daunus (Walcott) XCV: 2. 2a-c. 
 
 desmopleura (Meek) XCVI: 1. la-r. 
 
 desmopleura nympha (Walcott) XCVI: 2. 
 
 7 diablo (Walcott) XCIII: 3. 
 
 doris (Walcott) XCVII: 13, 13a. 
 
 hastingsensis (Walcott) XCI V: 3. 3a-c. 
 
 iddingsi (Walcott) XCI: 3, 3a-b. 
 
 indianola (Walcott) XCIV: It, 2. 2a-h. 
 
 johannensis (Matthew) XCVII: 10, 10a. 
 
 kayseri (Walcott) XCVII: 6, 6a-b. 
 
 kichouensis (Walcott) LXXXIX: 5. 
 
 linnarssoni (Kayser) XCVII: 5, 5a. 
 
 uewberryi Walcott Te.xt flgs. 69.\-D, 
 
 p. 783. 
 
 newtonensis (Weller) XCVII: 9, 9a. 
 
 pagoda (Walcott) XCVII: 12, 12a-d. 
 
 papias (Walcott ) XCI: 4. 
 
 primordialis(de Verneuil and Barrande) XCVII: 1, la-d. 
 
 remnicha(Winchell) XCI: 1, la-s; 
 
 XCII: 2, 2a-d; 3, 
 
 3a-e; 
 Text flg. 7, p. 299. 
 
 remnicha sulcata (Walcott) XCII: 1, la-c. 
 
 remnicha te.xana (Walcott) XCII; 4, 4a-g. 
 
 remnicha winfieldensis (Walcott) XCI: 2, 2a-e. 
 
 saltensis (Kayser) XCVII: 11. 
 
 tatei (Etheridge) XCVII: 15, 15a. 
 
 thyone Walcott Text figs. 70A-C, 
 
 p. 789. 
 
 tullbergi (Walcott) XCV: 3. 
 
 wichitaensis (Walcott) XCIV: 1, la-o, lu. 
 
 wichitaensis laniusculus (Walcott) XCIV: Ip-s. 
 
356 
 
 CA^IBRIAN BRACHIOPODA. 
 
 Boorthls wlmanl (Walcott) XCV: 4, -ta-d. 
 
 zeno Walcott Text figs. 71A-B, 
 
 p. 792. 
 
 sp. undt. a (Pompeckj) Not figured. 
 
 sp. undt. b (Pompeckj) Not figured. 
 
 sp. undt. c (Walcott) LXXXIX:7. 
 
 sp. undt. d Walcott LX XXIX : 8. 
 
 sp. undt. e Walcott Not figiu-cd. 
 
 Eostrophomcna elegantula (Walcott) XCV: G, Ga-b. 
 
 eretla [ Ni.'iiisla ( Jamesclhi)], Walcott CI: 5, 5a-b. 
 
 eros [Lingulella (LingulepLs)], (Walcott) XXXIX: 9, 9a. 
 
 eryx [.\crolheIe matthewn], Walcott LXI: 2. 
 
 escasoni(0 bolus (Westonia)], (.Matthew) XLIX: 1, la-f. 
 
 esthonia [.Schizambon?], Walcott LXXXIV: 4. 
 
 etheridgei(Huenella], Walcott LXXXIX: 9,9a. 
 
 etheridgei [ Micromitra ( Paterina)], (Tate) Ill: 10. lOa-c. 
 
 euglyplius[Obolus (Westonia)], (Walcott) XLVIII: 1, la-f. 
 
 eurekensis[Orusia?], (Walcott) CI: 7, 7a. 
 
 excelsis [Trematobolus], Walcott LXXXII: 8, 8a-b. 
 
 exigua [Lingulella (Lingulepis)], (Matthew) XXXIII: 4, 4a; 
 
 XLIII: 1, la-z. 
 
 exlmia [Lingula?], Barrande XXXII: 3. 
 
 cxporrecta [ Billingsella], ( Linnarsson) LXXX VIII: 1, la^l. 
 
 exporrecta rugosicostata [ Billingsella], Walcott LXXXVIII: 2,2a-c. 
 
 favosa [Obolella{Glyptias)], (Linnarsson) LV: 2, 2a-d. 
 
 feistmanteli[Obolus], (Barrande) XII: 1, la-f; 9, 9a. 
 
 ferraginea [Lingulella], Salter XXIX: 1, la-w; 
 
 XXIX: 2,2a-f; 
 XXX: 1; 
 XXXI: 3, 3a-c; 
 XXXV: 4, 4a-b. 
 
 of. ferruginea [Lingulella], Walcott XXX: 4. 
 
 Jestinata[Nisusia], (Billings) C: 1, la-j; 2, 2a-c; 
 
 Text fig. 6, p. 299. 
 
 festinata transversa [Nisusia], (Walcott) C: 4, 4a-b. 
 
 finkelnburgi [Finkelnburgia], (Walcott) XCIII: 2, 2a-e. 
 
 Flnkelnburgia finkelnburgi (Walcott) XCIII: 2, 2a-e. 
 
 osceola (Walcott) XCIII: 1, la-h. 
 
 osceola corrugata ( Walcott) Not figured. 
 
 finlandensis [Obolus (Westonia)J, Walcott XLVIII: 3, 3a^b. 
 
 flumenis [Lingulella] , (Matthew) XXXV: G, 6a-b. 
 
 (Fordinia) bellulus [Obolus], (Walcott) LI: 3, 3a-f. 
 
 gilberti [Obolus]. Walcott LI: 5, 5a-d. 
 
 perfectus [Obolus], Walcott LXIII: 10, lOa-d. 
 
 formosa [Mickwitzia], (Wiman) VI: 3. 3a-c. 
 
 fragilis [Obolus], (Walcott) XXIII: 5, 5a-e. 
 
 frankUnensis [Lingulella], (Walcott) XXVI: 3, 3a-b. 
 
 fuchsi [Lingulella], Redlieh XXXIX: 2, 2a-c; 3. 
 
 gamagei [.-Vcrothele], (Ilobbs) LX: 5, 5a-c. 
 
 gemma [.Vcrotreta], Billings LXVI: 1, la-b. 
 
 gemma [Bicia], (Billings) L: 1, la-n. 
 
 getmnula [.Vcrotreta], Matthew LXVJ: 3, 3a-c; 
 
 LXXVII: 5, 5a-f. 
 
 gilberti [Obolus (Fordinia)], Walcott LI: 3, 5a-d. 
 
 girtyi [Linnarssonella], Walcott LXXVIII: 5, ,5a; 
 
 LXXIX: l.la^r. 
 
 (Glyptias) favosa [Obolella], (Linnarsson) LV: 2, 2a-d. 
 
 gracia [.Vcrotreta]. Walcott XL VI: 5, 5a-d. 
 
 grandis [Lingulella], (Matthew) XXXVIII: 2,2a^f. 
 
 grandis (Lingulella IrF-vis], Matthew XIX: 4c. 
 
 granulata [ Vcrothele (Redlichella)], (Linnarsson) . .LVI: 2, 2a-n. 
 
 granulata [Botsfordia], (Redlieh) LVII: 4, 4a~r. 
 
 granulata [Discinolepis], Waagen LXXXI: 3, 3a-b. 
 
 granulata [Kutorgina], Matthew V: 5, 5a-c. 
 
 granvillensis [Lingulella], Walcott XXII; 1, la-d. 
 
 greg\va [Lingulella (Lingulepis)], (Matthew) XLIV: 1, la-p. 
 
 gregwarobusta [Lingulella (Lingulepis)l, (Matthew). Not figured. 
 
 groomi (Obolella], Matley Text fig. 52, p. 596. 
 
 gulielmi [Discinopsis] (Matthew) LXXXII: 5, 5a-c. 
 
 harlanensis [ Wimanella], (Walcott) LXXXVII: S, 5a-d. 
 
 hastingsensis [Eoorthls], (Walcott) XCrV: 3, 3a-c. 
 
 haydeni (Micromitra), Walcott Text figs. 20.V-D, 
 
 p. 33S. 
 
 hayesi [Lingulella], (Walcott) XXV: 1, la-j. 
 
 hebertl [Lingulella], Barrois XXXIX: ll,lla-c. 
 
 helena (Lingulella], (Walcott) XXrV:3,3a-d. 
 
 helena [Protorthb], Walcott XCIX: 4, 4a-b. 
 
 Helmersenia ladogensls (.Teremejew) LXIII: 7, 7a-f. 
 
 hera [ Vcrothele subsldua), Walcott LX: 9. 
 
 hlcksl I Billingsella], (Salter MS.) (Davidson) XCVII: 7, 7a-f. 
 
 highlandensis (lijllingsella], ( Walcott) LXXXVU: 4, 4st-c. 
 
 HueneUa abnormis (Walcott) CIII: 2,2a-m; 
 
 Text fig. 13, p. 299. 
 
 bilUngsi (Walcott) CII: 5, Sa-c 
 
 etheridgei Walcott LXXXIX: 9,9a. 
 
 lesleyi Walcott Text figs. 75.\-C, 
 
 p. 807. 
 
 orlentalis ( Walcott) CI V : 3 :ia-b. 
 
 texana (Walcott) CIII: l.la-L 
 
 texana licviusculus (Walcott) Not figured. 
 
 vennontana Walcott Text fig. 70, p. 809. 
 
 humilUma ( Lingulella?], (Barrande) XXX: 12. 
 
 hunnebergensis | Protorthis?], Walcott XCV: 5, 3a-c 
 
 ida [Elkania], ( Billings) XXX: 20, 20a; 
 
 LI: 4, 4a-c. 
 
 idahoensis [.\crotreta], Walcott LXV: 1, la-i; 
 
 LXVIII: 2, 2a-g. 
 
 cf. idahoensis [ Acrotreta], Walcott Not figiu-ed. 
 
 idahoensis alta [Acrotreta], Walcott LXV: 4, 4a-b. 
 
 idahoensis sulcata [Acrotreta], Walcott LXV; 5. 
 
 iddingsi [Eoorthis], (Walcott) XCI: 3, 3a-b. 
 
 inchoans [.Vcrotreta], (Barrande) XV: 7, 7a. 
 
 indianola [EoorthLs], (Walcott) XCIV: It, 2, 2a^h. 
 
 inflata [Acrotreta], (Matthew) LXX^^: 1, la-k; 
 
 2,2a. 
 
 ? inflatus (Obolus), Westergird Not figured. 
 
 ingricus[Obolusapollinis], (Eichwald) Not figured. 
 
 ino [LinguleUa], (Walcott) XX VI: 4, 4a-b. 
 
 insiguis [Trematobolus], Matthew •. LXXXIV: 5, 5a-c 
 
 insons [Lingulella?]. (Barrande) XXXII: 2, 2a-e. 
 
 insula; [Lingulella atava], (Matthew) XXXV: 8, 8a. 
 
 intermedia [.Vcrothele], Linnarsson LVI: 3, Sa-d. 
 
 Inyoensis [Wimanella], Walcott Text figs. G3A-B, 
 
 p. 747. 
 
 iole [LinguleUa], (Billings) XXVII: 5,5a. 
 
 (Iphidella) louise [Micromitra], Walcott Text figs. 31 A-B, 
 
 p. 359. 
 
 nyssa [Micromitra], Walcott Ill: 9, 9a. 
 
 omatella [Micromitra], (Linnarsson) Ill: 6, Ga-d. 
 
 pannula [Micromitra], (White) rV: 1, la-t; 3, 3a; 
 
 Text fig. 32, p. 36i 
 
 parmula maladensis [Micromitra], (Walcott). .IV: 2, 2a-g. 
 
 pannula ophirensis [Micromitra], (Walcott)...IV: 4, 4a-f. 
 
 iphis [Obolus (Westonia)], Walcott XLIX: 4, 4a-d. 
 
 irene [LinguleUa], (Billings) XXVII: 6,6a. 
 
 iris [ LinguleUa], (BUlmgs) XXVII: 2. 
 
 ismene [Obolus], Walcott XI: 3, 3a-b. 
 
 Isse [LinguleUa], (Walcotti XXXIX: 4,4a-b; 
 
 Text figs. 43A-F, 
 p. 510. 
 (JameseUa) amii [Nisusia], Walcott CI: G, Ga-b. 
 
 argent a [Nisusia], Walcott CI: 9, 9a-b. 
 
 erecta [Nisusia], Walcott CI: 5, 5a-b. 
 
 ? kanabensis [Nisusia] Walcott Not figtired. 
 
 k-uthani [Nisusia], (Pompeckj) CI: 4, 4a-b. 
 
 lowi (Nisusia], Walcott Text figs. Gl.\-D, 
 
 p. 734. 
 
 nautes [Nisusia), (Walcott) XCIII: G, 6a-b. 
 
 peUico[Nisusia],(deVemeuU and Barrande).. XCVII: 2, 2a-b. 
 
 perpast a [Nisusia], (Pompeckj) CI: 1, la-h. 
 
 perpasta macra [Nisusia], (Pompeckj) CI: 3, 3a. 
 
 perpastasubquadrata[Nisusia], (Pompeckj). .CI: 2, 2a-b. 
 
 spencei [Nisusia], (Walcott) XCIII: 7, 7a; 
 
 Text fig. G2, p. 737. 
 
 utahensis[Nistisia]. Walcott CI: 10, 10a. 
 
 jamesi[Plectorthis], (HaU) XCVl: 5, 5a-c. 
 
 johannensis [Eoorthis], (Matthew) XCVII: 10, 10a. 
 
 kanabensis [Nisusia? (JameseUa?)], Walcott Not figured. 
 
 kayseri [ Eoorthis], (Walcott) XCVII: 6, 6a-b. 
 
 kempanum [Trematobolus], (Matthew) LXXXIII: 1, la-o. 
 
 Keyserlingia buchi (de Vemeuil) LXXXI: 4, 4a-e. 
 
 kichouensis [Eoorthis], (Walcott) LXXXIX: 5. 
 
 kiurensis [LinguleUa], (Waagen) XXX: S, 5a; 6, 6a. 
 
 kuthani [Nisusia (JameseUa)], (Pompeckj) CI: 4, 4a-b. 
 
 kutorgaj [Acrotreta], Walcott LXV: 3, ,3a-e, g-k; 
 
 Text flg. 5S, p. 692. 
 
 Kutorgina cingulata (Billings) V: 1, la-s; 
 
 Text flp. 3 and 8, 
 p.299,and50A-C, 
 p. 581. 
 
INDEX. 
 
 357 
 
 Kutorgina granulata Matthew V: 5, 5a-c. 
 
 peculiaris (Tate) V: 2. 
 
 pemgata VValcott V: 3, 3a-e. 
 
 sardiniaensis Walcott V': 4, 4a-c. 
 
 sp. undt. Walcott Not figured. 
 
 labradorica [Micromitra ( raterina)], (Billings) 11:2, 2a-f. 
 
 labradoricaorientaiis[Micromitra(Paterina)], (Wal- 
 cott) II: 2. 
 
 labradorica swaiitouensis [Micromitra (Paierina)], 
 
 (Walcott) 11: 3, 3a-f. 
 
 labradorica utatiensis [Micromitra (Paterina)],(\^■al- 
 
 cott) 11: 8, Sa; 
 
 Text fig. 24, p. 350. 
 labradorica var. [Micromitra (Paterina)] Walcott.. .Not figured. 
 
 ladogensis [Helmersenia], (Jeremejew) LXIII: 7, 7a-f. 
 
 Isevis [ Acrothele subsidua], Walcott Not figured. 
 
 terts [Lingiilella], Matthew XIX: 4, 4a-b. 
 
 Iseris grandis [Lingulella], Matthew XIX: 4c. 
 
 l8e%-is [Protorthis], Walcott XCIX: 6, 6a-b. 
 
 IfeWusculus [Eoorthis wichitaensis], (Walcott) XCIV: Ip-s. 
 
 IgeWusculus [Huenella te.xana] (Walcott) Not figured. 
 
 lamborni [Obolus], (Meek) XXII: 2, 2a-Q. 
 
 lamborni minimus [Obolus], (Walcott) XXV: 4. 4a-b. 
 
 lamellosus [Obolus (Westonia?)], (Barrande) XII: 7, 7a-d. 
 
 lata [Acrothele matthewi], Matthew LXI: 3. 
 
 lateralis [Syntrophia], (Wtiitfleld) CII: 6, Oa-g; 
 
 Text fig. 11, p. 299. 
 
 latourensis [Protorthis], (Matthew) XCIX: 3, 3a-d. 
 
 leda [Obolus tetonensis], Walcott Not figured. 
 
 lens [Lingulella], (Matthew) XXXIII: 1, la-d. 
 
 lens [Obolus ( Pateobolus) bretonensis], (Matthe%v).Not figured. 
 
 lenticularis [Orusia], (Wahlenberg) XCV'III: 1, la-p; 2, 
 
 2a-k; 3, 3a-b; 6, 
 6a-d. 
 
 lenticularis atrypoides [Orusia], (Matthew) XCVIII: 5. 
 
 lenticularis lyncioides [Orusia], (Matthew) XCVIII: 4. 
 
 leos [tingulella], (Walcott) XXIV: 2, 2a-c. 
 
 lepis [Lingulella], (Salter) XXXI: 4, 4a-f. 
 
 (Leptembolon) lingulseformis [Lingulella], (Mick- 
 
 witz) XIV: 5, 5a-b. 
 
 lesleyi [Huenella], Walcott Te.xt figs. 75A-C, p. 
 
 807. 
 
 levisensis [Acrothele], Walcott LXXXI: 12, 12a-b. 
 
 limoensis [.\crotreta uplandica], (Wiman) LXX: 4, 4a-c. 
 
 lindstromi [Billingseila], (Linnarsson) LXXXVII: 0, Oa-f. 
 
 lindstromi [Obolella ?], Walcott LV: 4, 4a. 
 
 lineolata [Lingulella], (Walcott) XLVIII: 2, 2a-l. 
 
 Lingula anatina Brugui&re Text figs. 34C-D, p. 
 
 374. 
 
 Llngula ? exinila Barrande XXXII: 3. 
 
 lingulseformis [Lingulella (Leptembolon)], (Mick- 
 
 witz) XIV: 5, 5a-b. 
 
 Lingulella acutangula ( Roemer) XVII: 1 , la-o. 
 
 agnosforum ( Wallerius) XXX: 15. 
 
 ampla (Owen) XXVIII: 1, la-j. 
 
 arguta (Walcott) XXIV: 5. 5a-b. 
 
 atava (Matthew) XXXV: 5.5a-h. 
 
 atava insuire (Matthew) XXXV: 8,8a. 
 
 auga ( W alcott) XX IV: 0, 6a-g. 
 
 bella ( Walcott) XIX:2, 2a-q; 
 
 XXXVI: 4. 
 
 bellula (Walcott) XIX: 1 , la-e. 
 
 billingsiana (Whiteaves) XXIX: 3, 3a. 
 
 bornemanni (Walcott) XXX: IS, 18a-c. 
 
 buttsi Walcott XXIX: 4, 4a-b. 
 
 cania (Walcott) XXX V: 3, 3a-d. 
 
 cedens ( Barrande) XXX: 8. 
 
 clarkei Walcott Text figs. 42.\.-D, p. 
 
 486. 
 
 coUlcia (Matthew) XXXV: 1, la-f: 2, 
 
 2a-d. 
 
 concinna Matthew XXXIII: 2, 2a-h; 
 
 XXXIV: l,la-r. 
 
 cuneola (Whitfield) XXVII: 7, 7a-b. 
 
 damesi (Walcott) XXXIX: 8, Sa-c. 
 
 davidsoni (Barrande) XXXII: 1, la-«. 
 
 davisi (McCoy) XXX: 2, 2a; 
 
 XXXI: 6, 6a-h. 
 
 LinguleUa delgadoi Walcott XXIX: 6,6a-c. 
 
 desiderata ( Walcott) XX: 4, 4a-c; 5, 5a-j. 
 
 dubia (Walcott) XXIV: 4, 4a. 
 
 ellsi ( Walcott) XIX: 3, 3a-c. 
 
 terruginea Salter XXIX: 1, la-w; 
 
 XXIX:2,2a-f; 
 
 XXX: 1; 
 
 XXXI: 3,3a-c; 
 
 XXXV: 4, 4a-b. 
 
 of. ferruginea W^alcott XXX: 4. 
 
 flumenis (Matthew) XXXV: 0, 6a-b. 
 
 franklinensis (Walcott) XXVI: 3, 3a-b. 
 
 fuchsi Itedlich XXXIX: 2, 2a-c; 3. 
 
 grandis (Matthew) XXXVIII: 2, 2a-I. 
 
 granvillensis Walcott XX: 1 , la-d. 
 
 hayesi (Walcott) XXV: 1, la-j. 
 
 heberti Barrois XXXIX: 11, lla-c. 
 
 helena (Walcott) XXIV: 3, 3a-d. 
 
 ? humiUuna ( Barrande) XXX: 12. 
 
 ino( Walcott) XXVI: 4, 4a-b. 
 
 ? insons (Barrande) XXXII: 2, 2a-e. 
 
 iole ( Billings) XXVII: 5, 5a. 
 
 Irene ( Billings) XXVII: 0, 6a. 
 
 iris (Billings) XXVII: 2. 
 
 isse (Walcott) XXXIX: 4, 4a-b; 
 
 Text figs. 43.\-F, p. 
 510. 
 
 kiurensis (Waagen) XXX: 5, 5a; 6, 6a. 
 
 Ia3vis Matthew XIX: 4, 4a-b. 
 
 laevis grandis Matthew XIX: 4e. 
 
 lens (Matthew ) XXXIII: 1, la-d. 
 
 leos (Walcott) XXIV: 2, 2a-c. 
 
 lepis (Salter) XXXI: 4, 4a-I. 
 
 lineolata (Walcott) XLVIII: 2, 2a-l. 
 
 linnarssoni (Walcott) XXX: 14, 14a. 
 
 manticula (White) XX: 1, la-c. 
 
 manticula var Not figured. 
 
 martinensis Matthew XXXVIII: 1, la-& 
 
 minor (Matthew) XXXVII: 3, 3a-g. 
 
 mosia (Hall) XVIII: 1, la-t. 
 
 mosia osceola (Walcott) XVIII: 2, 2a-c. 
 
 namio (Walcott) XXIV: 1 , la-d. 
 
 nathorsti Linnarsson XXXI: 1, la-h. 
 
 nicholsoni Callaway XXX: 3, 3a-f. 
 
 ora (Walcott) XXXV: 9, 9a-d. 
 
 oweni (Walcott) X VIII: 5, oa-f. 
 
 perattenuata (Whitfield) XXI: 1, la-i. 
 
 phaon (Walcott) XXVI: 1, la-e. 
 
 pogonipensis (Walcott) XX: 3, 3a-c. 
 
 prima (Conrad MS.) (Hall) XXVII: 1, la-c 
 
 ? prima?va Hicks XXXI: 5, 5a. 
 
 punctata (Walcott) XX: 6, 6a. 
 
 quadrilateralis (Walcott) XXXIX: 6, 6a. 
 
 radula Matthew XLV: 1, la-1. 
 
 randomensis (Walcott) XXI: o, 5a. 
 
 rotunda ( Matthew) XXXVII: 3h-k. 
 
 sehucherti (Walcott) XXI: 6. 
 
 siemiradzkii (Walcott) XXXI: 2, 2a. 
 
 signata (Barrande) XXX: 11. 
 
 similis (Walcott) XXI:2,2a-i;3,3a-d. 
 
 ? simplex (Barrande) XXXII: 4, 4a-b. 
 
 tarpa (Walcott) XXIII: 2, 2a-c. 
 
 texana Walcott XLIX: 3, 3a. 
 
 torrentis ( Matthew) XXXV: 7. 
 
 triparilis (Matthew) XLV: 2, 2a-f; 
 
 Text" figs. 44a-l, 
 p. 537. 
 
 tumlda Matthew XXIV: 7, 7a-d. 
 
 upis (Walcott) XXXVI: 3,3a. 
 
 wanniecki Redlich XXXIX: 1, la-n. 
 
 welleri (Walcott) XXXVIII: 4, 4a-b. 
 
 Winona (Hall) XVIII: 3, 3a-b. 
 
 Winona convexa (Walcott) XVIII: 4, 4a-<l. 
 
 wlrthi (Barrande) XXX: 7. 
 
 zeus Walcott Text fig. 45, p. 541. 
 
 sp. undt. a Walcott XXX: 13. 
 
 sp. undt. b Walcott Not figured. 
 
 LinguleUa (Leptembolon) lingulseformis (Mickwdtz) XIV: 5, 5a-b. 
 
358 
 
 CMIBRIAN BRACHIOPODA. 
 
 Llngulella (Lingulepis) acuminata (Conrad) XXXIV: 3, 3a-e; 
 
 XL: 1, lar^; 
 XLI: 1, la-n; 
 XLII: l,la-o. 
 
 acuminata meeki ( Walcott) XLI: 2, 2a. 
 
 acuminata sequcns Walcott Text flgs. 46 A-B , 
 
 p. 5ol. 
 
 eros (Walcott) XXXIX: 9, 9a. 
 
 exigua (Matthew) XXXIII: 4, 4a; 
 
 XLIII: 1, la-z. 
 
 gregwa (Matthew) XLI V: 1, la-p. 
 
 grcgrvva rol>usta (.Matthew) Not figured. 
 
 longinerris (Matthew) XLIV: 2, 2a-g. 
 
 pumUa (Matthew) XLV: 3,3a. 
 
 7 pygmiea (Salter) XXX: 10. 
 
 roberti (Matthew) XXXVII: 4, 4a-d. 
 
 rowei (Walcott) XXI: 4.4a-b. 
 
 spatula (Walcott) XIX : 5, oa-b. 
 
 ? squamosa (Holl) XXX: 9. 
 
 starri (Matthew) XXXVII: 2,2a-b. 
 
 ? sp. undt. (Walcott ) Not figured. 
 
 (Lingulobolus) affinis [Obolus], (Billings) XVI: l,la-e. 
 
 spissus [Obolus], (Billings) XVI: 2, 2a-k; 
 
 XLII: 3,3a. 
 
 Linnarssonella girtyi Walcott LXXVIII: 5, oa; 
 
 LXXIX: l,la-r. 
 
 mmuta (Hall and Whitfield) LXXIX: 2. 2a-b. 
 
 modesta Walcott LXXVIII: 8. 8a-f. 
 
 nitens Walcott LXXVIII: 7, 7a. 
 
 tennesseensis Walcott LXXIX: 3,3a-k. 
 
 transversa Walcott LXXVIII: 6. 6a-c. 
 
 urania Walcott LXXVIII: 9, 9a-c. 
 
 linnarssoni |Eoorthis], (Kayser) XC VII: S. 5a. 
 
 linnarssoni [Lingulella], (Walcott) XXX: 14, 14a. 
 
 lisani | Acrotreta], Walcott LX VIII: 3, 3a-c. 
 
 loganilMicromitra(Paterina)], (Walcott) II: 6.6a-b. 
 
 longinervis [Lingulella (Lingulepis)], (Matthew)... .XLIV: 2, 2a-g. 
 
 lopori [Obolus], Walcott IX : 4, 4a. 
 
 ( Loperia) dugaldensis ( Protorthis], Walcott XCIX: 5, 5a-j. 
 
 louise [Micromitra (Iphidella.i], Walcott Te.xt figs. 31.\-B, 
 
 p. 359. 
 
 lowi [Xisusia (Jamesella)], Walcott Text figs. 61.V-D, 
 
 p. 734. 
 
 lusitanica [Delgadella], (Delgado) XXIX: 5,5a-b, 
 
 Iyncioides[Orusialenticularis], (Matthew) XCVIII: 4. 
 
 mcconnelli [Obolus], (Walcott) XXlII:3,3a. 
 
 mcconnelli decipiens [Obolus], Walcott XXIII: 4, 4a-b. 
 
 mcconnelli pelias [Obolus], (Walcott) XXIII: 3b-c: 
 
 XXXIX: 5,5a-c. 
 macra [Xisusia (Jamesella) perpasta], (Pompeckj) . .CI: 3,3a. 
 
 maculata [.\crothele], (Salter) LVII: 2, 2a-b; 
 
 LVIII: 2. 
 
 mffira [Obolus], (Hall and Whitfield) X: 2, 2a-e. 
 
 magna [.Vcrotreta sagittaUs], (Matthew) LX VI: 4, 4a-f. 
 
 major [BillingseUa], Walcott LXXXVI: 1,1a. 
 
 major [Micromitra ( Paterina)], (Walcott) Text fig. 25, p. 351 . 
 
 major [Rustella?], (Matthew) Text fig. 19, p. 328. 
 
 maladensis [Micromitra (Iphidella) pannula], (Wal- 
 cott) IV: 2, 2a-g. 
 
 manitouensis [Schizambon], Walcott LXXXIV: 3,3a-e. 
 
 manticula [Lingulella], (White) XX: l,la-c. 
 
 marion [BillingseUa], Walcott Text figs. 67 A-B , 
 
 p, 758, 
 
 marjumcnsis [.Vcrotreta], Walcott LXXVIII: 2, 2a-d. 
 
 martinensis [Lingulella], Matthew XXXVIII: 1, la-g. 
 
 matinalis [Obolus], (HaU) .VIII: 1, la-k. 
 
 matinalis ? (Obolus], Walcott VIII: 3, 3a. 
 
 mat thcwi [ Acrothele], (Tlartt) LXI: 1, la-g. 
 
 matthewi eryx [.Vcrothcle], Walcott LXI: 2. 
 
 matthewi lata [.\crothele], Walcott LX 1:3. 
 
 matthewi multicostata [.Vcrothcle], Matthew LXI: 5, 5a-c. 
 
 ma.\imus [Obolus apoUinis], .Mickwitz VII: 9; 
 
 XIV: 7, 7a. 
 meekl [Lingulella (Lingulepis) aciuninata], (Wal- 
 cott) XLI: 2,2a. 
 
 membranaceus [Obolus], Walcott Text figs. 36.\-B, 
 
 p. 4(Xi. 
 
 meneghini [Obolus?], Walcott X.\.\ : 17, 17a. 
 
 (Mickwilzella) siluricus [Obolus), (Eichwald) XV: 1, la-c. 
 
 mickwiizi [Obolus], Walcott X: 1, la-k. 
 
 Mickwitzia formosa (Wiman) VI: 3, 3a-c. 
 
 monililera (Llnnarsson) VI: 1, la-p; 
 
 LIX: 2. 
 
 occidens Walcott VI: 4. 
 
 pretiosa Walcott VI: 2. 
 
 7 sp. undt. Walcott Not figured. 
 
 Micromitra alabamaensis (Walcott) II: 5, 5a-c. 
 
 haydeni Walcott Text flgs. 20.\-D, 
 
 p. 338. 
 
 nisus (Walcott) II: 10. 
 
 pealei (Walcott) Ill: 3, 3a-e. 
 
 pusilla ( Llnnarsson) Ill: 2, 2a-c. 
 
 scotica Walcott Text flgs. 21 A-C, 
 
 p. 340. 
 
 sculptilis (Meek ) IH: 3, 5a-e. 
 
 sculptilis endlichi Walcott Textflg. 22, p. 342. 
 
 zenobia Walcott Text fig. 23, p. :J42. 
 
 sp. undt. (Walcott) Ill: 7. 
 
 Micromitra (Iphidella) louise Walcott Text figs. 31.\-D 
 
 p. 359. 
 
 nyssa Walcott Ill: 9, 9a. 
 
 ornatella (Llnnarsson) HI: 6, 6a-d. 
 
 pannula (White) IV: I, la-t; 3,3a; 
 
 Text fig. 32, p. 362. 
 
 pannula maladensis (Walcott) IV: 2, 2a-g. 
 
 pannula ophirensis (Walcott) IV: 4, 4a-f. 
 
 Micromitra ( Paterina) bella (BilUngs) U: 1, la-c. 
 
 crenistria (Walcott) Ill: 4, 4a-b. 
 
 etheridgei (Tate) '. .Ill: 10, lOa-c. 
 
 labradorica (Billings) II: 2, 2a-f. 
 
 labradorica orientalis (Walcott) II: 11. 
 
 labradorica swantonensis (Walcott) II: 3, 3a-f. 
 
 labradorica utahensis (Walcott) U: 8, 8a; 
 
 Textflg. 24, p. 330. 
 
 labradorica var. Walcott Not figured. 
 
 logani (Walcott) II: 6, 6a-b. 
 
 major ( Walcott) Text fig. 23, p. 351. 
 
 philhpsi ( HoU) UI: 8. 
 
 prospectensis (Walcott) 11: 4, 4a. 
 
 stissingensis (Dwight) Ill: 1, la-e. 
 
 stissingensis ora Walcott Not figured. 
 
 stuarti Walcott Text figs. 2«.\-B, 
 
 p. 333. 
 
 superba (Walcott) II: 7, 7a-f; 
 
 Text figs. 27.\-B, 
 p. 333. 
 
 undosa (Moberg) Text flgs. 28A-C, 
 
 p. 356. 
 
 waptaWalcolt Te.xt flgs. 29.\.-B, 
 
 p. 357. 
 
 williardi Walcott....'. II: 9b-c; 
 
 Text figs. 30.\-E, 
 p. 33S. 
 
 microscopica [.\crolreta], (Shumard) LXVII: 1, la-h, lo, 
 
 2, 2a-d. 
 
 microscopica missouriensis [Acrotreta], Walcott LXVII: 4, 4a-b 
 
 microscopica tetonensis [.Vcrotreta], Walcott LXVII: 3, 3a-d. 
 
 minima [.\crotreta 7], (Barrande) LXXVII: 7,7a. 
 
 minimus [Obolus], Walcott XI: S, 8a. 
 
 minimus [Obolus lamborni], (Walcott) XV: 4, 4a-b. 
 
 minor [.Vcrothyra], Walcott LXX VI: 4, 4a-b, 
 
 minor [Lingulella], (.Matthew) XXXVII: 3,3a-g. 
 
 minor [Obolella], (Walcott) LIV: 3,3a-d. 
 
 minor [Obolus?], Barrande XV: 6. 
 
 minuta [ .V crothele], Walcott LXIU: 3. 
 
 minuta [Linnarssonella], (Hall and Whitfield) LXXIX: 2,2a-b. 
 
 miqueli ( Vorkia?], Walcott LXXXII: 4. 
 
 mirandus [Obolus?], (Barrande) XII: 4,4a. 
 
 misera [Acrotreta], (Billings) LXXII: 2,2a-L 
 
 missouriensis | .Vcrotreta microscopica),WaIcott LXVII: 4, 4a-U 
 
 mobergi [Obolella]. Walcott LV: 3. 3a-f. 
 
 mode-sta [Linnarssonella], Walcott LXXVIII: S,Sa-f. 
 
 monilifera [Mickwitzia], (Llnnarsson) VI: l,l3-p; 
 
 LIX: 2. 
 
 montanensis [Clarkella], (Walcott) CIV: 2,2a-d. 
 
 mosia [Lingulella], ( Hall) XVIII: 1, la-f. 
 
 mosia osceola [Lingulella], (Walcott) XVIII: 2,'2,">-c. 
 
 multicost<ita [Vcrothele matthewi], Matthew LXI: 5.5a-c. 
 
 multisecta [Dalmanella], (Meek) Text fig. 9, p. 299. 
 
 murrayi [Obolus?], Billings XV: 12, 
 
INDEX. 
 
 359 
 
 namouna (Obolus], Walcott VIII: 2, 2a. 
 
 nanno [Lingulella], ( Walcott) XXIV: 1 , la-d. 
 
 nanus [Dicellomus], (Meek and Hayden) LIII: l,la^l; 2, 2a; 
 
 3.3ar-d. 
 
 nathorsti [Lingulella], Linnarsson XXXI: l.la^h. 
 
 nautes [Nisusia (Jamesella)], (Walcott) XCIII: 6, (ia-b. 
 
 neboensis [Acrotrcta], Walcott LXXVII: 9, 9a-b. 
 
 Neobolus warthi Waagen I: 3; 4,4a-b; 5.5a; 
 
 LXXXI: 2,2a-h; 
 Text figs. 47.\-B, 
 p. 567. 
 
 newberryi [Eoorthis], Walcott Te.xt figs. C9.V-D, 
 
 p. 783. 
 
 newtonensis [Eoorthis], ( Weller) XCVII: 9, 9a. 
 
 nicbolsoni [Acrotreta], Davidson LXXIII: l,la-k; C, 
 
 Ca-b. 
 
 nicbolsoni [Lingulella], Callaway XXX: 3,3a-f. 
 
 ninus [Obolus tetonensis], Walcott VIII: 11, lo; 
 
 XI: l,lar-g. 
 
 nisus [Micromitra], (Walcott) II: 10. 
 
 Nisusia alberta (W'alcott) C: 3,3a-d. 
 
 corapta (Tate) XCVII: 14. 
 
 lestinata (Billings) C: l,lar-j; 2,2a-c: 
 
 Te.xt fig. 6, p. 299. 
 
 lestinata transversa (Walcott) C: 4, 4a-b. 
 
 rara Walcott Text fig. 60, p. 730. 
 
 ?vaticina(de Vemeuil and Barrande) XCVII: 3,3a^b. 
 
 Nisusia (.lamesella) amii Walcott CI: 6. Tia-b. 
 
 ai genta Walcott CI: 9. 9a-b. 
 
 erccta Walcott. ..'. CI: 5.5a-b. 
 
 7 kanabensis Walcott Not figured. 
 
 kuthani ( Pompeckj ) CI: 4. 4a-b. 
 
 lowiWalcott Text figs. Ol.V-D, 
 
 p. 734. 
 
 nautes (W'alcott) XCIII: 0, (ia-b. 
 
 pellico (de Verneuil and Barrande) XCVII: 2,2a-b. 
 
 perpasta (Pompeckj) CI: l,la-li. 
 
 perpasta macra (Pompeckj) CI: 3, 3a. 
 
 perpasta subquadrata (Pompeckj) CI: 2.2a-b. 
 
 spencei (Walcott) XCIII: 7, 7a; 
 
 Text fig. U2,p. 737. 
 
 utahensis Walcott CI: 10. 10a. 
 
 sp. undt. Walcott Not figiKed. 
 
 nil ens [ Linnarssonella], Walcott LXXVIII: 7, 7a. 
 
 nitida [.\crothelel, ( Ford) LVIII: 4, 4a. 
 
 notchensis [Obolus (Westonia)), Walcott LXIII: 9. 
 
 nox [Acrotreta], Walcott LXXVII: 10. 
 
 nundina [Obolus], Walcott XI: 4, 4a. 
 
 nundina[Syntrophial, Walcott CII: 4, 4a-d. 
 
 nyuipha[Eoortliis desmopleura], (Walcott) XCVI: 2. 
 
 nyssa [Micromitra (Iphidella)], Walcott Ill: 9, 9a. 
 
 Obolella asiatica Walcott LV: C, Ca. 
 
 atlantica Walcott LV: la-i; 
 
 Text fig. 51, p. 590. 
 
 chromatica Billings LIV: 1, la-i. 
 
 crassa (HaU ) LI V : 2, 2a-n ; 
 
 Text fig. 14, p. 299. 
 
 crassa elongata Walcott LV: 5, 5a. 
 
 groomi Matley Text fig. 52, p. 596. 
 
 ? lindstromi Walcott LV: 4,4a. 
 
 minor (Walcott) LIV: 3, 3a-d. 
 
 mobergi Walcott LV: 3, 3a-f. 
 
 vcrmilionensis Walcott Text figs. 53A-E , 
 
 , p. 598. 
 
 wirrialpensis Etheridge LV: 7, 7a-b. 
 
 Obolella (Glyptias) favosa (Linnarsson) LV: 2, 2a^d. 
 
 Obolus acadicus Walcott XI: 5. 
 
 "?advenus Barrande XII: 5, 5a-b. 
 
 anceps Walcott X: 3, 3a-f. 
 
 ?ancillus (Barrande) XII: 2. 
 
 apoUinis Eichwald VIl: 1-8, 10-1 
 
 XIV: 6, Ga; 
 Text figs. 4 and 15, 
 p. 299. 
 
 apoUinis ingricus ( Eichw.ald) Not figured. 
 
 apoUinis maximus Mickwitz .-...VlI: 9; 
 
 XIV: 7, 7a. 
 
 apoUinis quenstedti (Mickwitz) Text figs. 34.\-B, 
 
 p. .374. 
 
 Obolus? bavaricus (Barrande) XV: 10, 10a. 
 
 belli (BiUings) XXXVIU: 3, ,3a-b. 
 
 chinensis (Walcott) XXXIX: 7, 7a-b. 
 
 complexus Barrande XII: 3, 3a; 8, 8a. 
 
 cyane(BUlings) , XXVII: 4, 4a-b. 
 
 discoideus (Hall and Whitfield) XVIII: 6, Ca-d. 
 
 dolatus (Sardeson) Text figs. 3oA-B, 
 
 p. 390. 
 
 eichwaldi Mickwitz Not figured. 
 
 elegans Mickwitz XV: 3. 
 
 leistmanteli (Barrande) XII: l,la-f; 9,9a. 
 
 fragilis (Walcott) XXIII: 5, 5a-e. 
 
 ? inflatus Westergird Not figured. 
 
 isniene Walcott XI: 3, 3a^b. 
 
 lamborni (Meek) XXII: 2, 2a-n. 
 
 lamborni minimus (Walcott) XXV: 4, 4a-b. 
 
 loperi Walcott IX: 4, 4a. 
 
 mcconnelli (Walcott) XXIH: 3, .3a. 
 
 mcconnellidecipiens Walcott XXIII: 4, 4a-b. 
 
 mccoimeUi pelias (Walcott) XXIII: 3b-c. 
 
 XXXIX: 5, 5a-c. 
 
 mtera (HaU and Whitfield) X: 2, 2a-e. 
 
 matinalis (Hall) VIII: 1, la-k. 
 
 matinalis?(lIaU) Walcott VIII: 3, .la. 
 
 membranaceus Walcott Text figs. 36A-B, 
 
 p. 403. 
 
 ?meneghini Walcott XXX: 17, 17a. 
 
 mickwitzi Walcott X: 1, la-k. 
 
 minimus Walcott XI: 8, 8a. 
 
 ? minor Barrande XV: 6. 
 
 ? mirandus (Barrande) XII: 4, 4a. 
 
 ? murrayi BUlings XV: 12. 
 
 namouna Walcott VIII: 2, 2a. 
 
 nundina Walcott XI; 4, 4a. 
 
 obscurus Walcott XI: 9, 9a-d. 
 
 ? palliatus Barrande XV: 5. 
 
 pandemia Walcott IX: 3, 3a-d. 
 
 panderi Mickwitz Not figiu-ed. 
 
 parvus Walcott Text figs. 37A-B, 
 
 p. 408. 
 
 pheres Walcott XI: 6, Ca-b. 
 
 prindlei (Walcott) XXVII: 3, 3a-e. 
 
 refulgens Matthew IX; 2, 2a-d. 
 
 rhea Walcott ^ IX: 1, la-c. 
 
 V rokitzanensis Barrande XII: 6. 
 
 rotundatus (Walcott) XX: 2, 2a-e. 
 
 schmalenseei (Walcott) XXX: 19, 19a-e. 
 
 Schmidt i Mickwitz XV: lla-c. 
 
 selwj-ni (Matthew) XXXVI: 1, la-h; 2, 
 
 2a-b; 
 
 XXXVn: l,la-f. 
 sept.alis (Walcott) XXIII: 3d; 
 
 XXXTV: 2, 2a. 
 
 shansiensis Walcott XI: 7, 7a-e. 
 
 since (Walcott) XXVI: 2, 2a-h. 
 
 smithi Walcott Text figs. 38A-B, 
 
 p. 416. 
 
 tetonensis Walcott IX: 5, 5a-d. 
 
 tetonensis leda Walcott Not figured. 
 
 tetonensis ninus Walcott VIII: 1 l-lo; 
 
 XI: 1, la-g. 
 
 ? torrentis Matthew Not figured. 
 
 triangularis Mickwitz Not figured. 
 
 volborthi Mickwitz Not figured. 
 
 wUlisi (Walcott) XXIII: 1, la-j. 
 
 wortheni Walcott IX: 5e; 
 
 Text figs. 39.A.-D, 
 p. 421. 
 
 zetus (Walcott) XXV: 3, 3a-c. 
 
 ? zoppi Walcott XXX: 16, 16a-b. 
 
 sp. undt. a Walcott X: 4. 
 
 sp. undt. b Walcott Not figm-ed. 
 
 sp. undt. c Walcott Not figured. 
 
 sp. undt. d Walcott Not figtired. 
 
 sp. undt. e Kayser XV: S. 
 
 ?sp. undt. f Kaj-ser XV: 9. 
 
 sp. undt. g Linnarsson Not figured. 
 
 Obohis (Acritis) antiquissimus (Eichwald) XIII: 3: 
 
 XV: 2, 2a-d. 
 
360 
 
 CAMBRIAN BRACHIOPODA. 
 
 Oboliis ( Acritis?) niRatiis Walcott X II I: 2 and 3. 
 
 Obolus(Broggeria)salteri(IIoll) XIII; 1, la-n; 
 
 XV: 4, 4a-d. 
 Obolus Fordlnia bellulus (Walcott) LI: 3: 3a-f. 
 
 gilberli Walcott LI: 5, 5a-d. 
 
 perfectus Walcott LXIII: 10,10a-d. 
 
 Obolus (Lingulobolus; afTinis (Billings) XVI: 1, la-c. 
 
 spissus( Billings) XVI: 2, 2a-k; 
 
 XLIl: 3,3a. 
 
 Ol)()liis(Mickwitzella)siliiricus(Eichwald) XV: 1, la-c. 
 
 Oboliis(Fal3eobolus) bretoneiLsis (Matthew) XXXII: 5, 5a-g. 
 
 bretonensis lens (Matthew) Not figured. 
 
 Obolus (Schmidtia) acuininatus Mickwitz XIV: 2 2a-c. 
 
 celatus (Volborth) XIV: 1, la-c. 
 
 crassus Mickwitz XI V: 4, 4a-d. 
 
 obtu.sus Mickwitz XIV: 3,3a-c. 
 
 Olwlus (Westonia) &landensis Walcott XLVIII: 6,6a. 
 
 aurora (HaU) XLVI: 1 , la-h. 
 
 balticus Walcott XLVIII: 7.7a-b. 
 
 blaekwelderi Walcott XXX IX: 10, lOa-c. 
 
 bottnicus ( Wiman) XLVIII: 4, 4a-c. 
 
 chuarensis (Walcott) XXV: 2,2a-e. 
 
 dartoni Walcott Text figs. 40A-C, 
 
 p. 465. 
 
 ella (HaU and Whitfield) XXXIII: 3, 3a-c; 
 
 XLVII: l,la-p. 
 
 ella ouaquiensis Walcott X LIX: 6, 6a. 
 
 elongatus Walcott LXIII; 8, Sa-d. 
 
 escasoni (Matthew) XLIX: l,la-f. 
 
 euglyphus( Walcott) XLVIII; l,la-I. 
 
 flnlandensis Walcott XLVIII: 3, 3a-b. 
 
 iphis Walcott XLIX: 4,4a-d. 
 
 1 lamellosus (Barrande) XII: 7.7a-d. 
 
 notchensis Walcott LXIII: 9. 
 
 rogersi (Walcott) XLII: 2,2a-d. 
 
 stoneanus (Whitfield) XXVIII: 2, 2a-g; 
 
 XLIX: 2,2a. 
 
 themis Walcott XI: 2.2a-c. 
 
 wasatchensis Walcott XLIX: 5, 5a: 
 
 Text figs. 41A-F, 
 p. 467. 
 
 wimani Walcott XLVIII: 5, .la-b. 
 
 sp. undt. a Walcott Not figured. 
 
 sp. undt. b Walcott Not figured. 
 
 obscura[BillingseIla]. Walcott LXXXVI: G. 
 
 obscurus [Obolus] , Walcott XI; 9, 9a-d. 
 
 obtusus [Obolus (Schmidtia)], Mickwitz XIV: 3,3a-c. 
 
 occidens [Mickwitzia], Walcott VI: 4. 
 
 oelandica [Acrotreta], Westergird Not figured. 
 
 onaquiensis [Obolus (Westonia) ella], Walcott XLIX: 6,6a. 
 
 ophirensis [ Acrotreta] . Walcott LXXIV: 1, la-p. 
 
 ophirensis [Micromitra (Iphidella) pannula], (Wal- 
 cott) IV: 4, 4a-f. 
 
 ophirensis descendens [Acrotreta], Walcott LXXVIII; 1 , la-c. 
 
 ophirensis rugosa [Acrotreta], Walcott LXXIV: 2,2a-e. 
 
 ora [Lingulella], (Walcott) XXXV: 9,9a-d. 
 
 Orbiculoidea contraria ( Barrande) LXXXI; 9. 
 
 pileolus ( Hicks MS.) (Salter) LXXXI: 11 , 11a. 
 
 varians (Barrande) LXXXI: 8. 
 
 orientalLs [ Billingsella], ( Whitfield) LXXXVI: 2, 2a-b. 
 
 orientalis [ Huenella], (Walcott) CIV: 3.3a-b. 
 
 orientalis [Micromitra (Paterina) labradorica], (Wal- 
 
 cott> II: 2. 
 
 orientalis [ Vorkia?] , Walcott LXXXII: 3, 3a. 
 
 ornatclla [Micromitra (Iphidella)]. (Linnarsson) III: G.6a-d. 
 
 orta [.\crothyra signata], Matthew LXXX; 3, 3a-b. 
 
 orthia [Syntrophia], Walcott CIV: 4,4a-b. 
 
 Orusia 1 eurekensis (Walcott) CI: 7, 7a. 
 
 lenticularis ( Wablenberg) XCVIII: 1 . la-p; 2, 
 
 2a-k; 3,3a-b; 6, 
 6a-c. 
 
 lenticularis atrypoides (Matthew) XC VI II: 5. 
 
 lenticularis lyncioides (Matthew) XCVIII: 4. 
 
 osceola [ Finkelnburgia] ,( Walcott) XC I II: I , la-h. 
 
 osceola [ Lingulella mosia] , ( Walcott) XVIII: 2, 2a-c. 
 
 osceola corrugata [ Finkelnburgia], (Walcott) Not figured. 
 
 Otusia sandbergi ( Winchell) XCll I: 4, 4a-d. 
 
 utahensis Walcott LXXXIX: 3, 3a-c. 
 
 ovalis [.Vcrotreta], Walcott XLVI: 2, 2a-b. 
 
 oweni [Lingulella], (Walcott) XVIII: 5,5a-f. 
 
 pacifica (Acrotreta), Walcott LXIX: 6, Oa-e. 
 
 pagoda [Ko»rthLs],(Walcottj XCVII: 12,12a-d. 
 
 (Palffiobolus) bretonensis[Obolu.s], (Matthew) XXXII: 5,5a-g. 
 
 bretonensis lens [Obolus], (Matthew) Not figured. 
 
 palliatus [Obolus ?], Barran'lc XV: 5. 
 
 pandemia [Obolus], Walcott IX: 3,3a-d. 
 
 panderi [.\crot hele], Walcott LIX: 5,5a-c. 
 
 panderi [Obolus], Mickwitz Not figured. 
 
 pannula [Micromitra (Iphidella)], (White) IV: l,la-t; 3, .3a; 
 
 Text fig. 32, p. 362. 
 pannula maladensis [Micromitra (Iphidella)], (Wal- 
 cott) IV: 2, 2a-g. 
 
 pannula ophirensis [Micromitra (Iphidella)], (Wal- 
 cott) IV: 4, 4a-f. 
 
 papias[Eoorthis], (Walcott) XCI: 4. 
 
 parva [Dalmanclla], (dc Vcrneuil) Text fig. 10, p. 299. 
 
 pari-a [ I'lecturt his), ( Dalman) XCVI: 6,(ia-g. 
 
 par\-ula[.\crolr(!ta], (Wallerius) LXXVII: 4.1a. 
 
 pan'US[Dicellomus], Walcott LXXXIX:ll,ll»-d. 
 
 parvus [Obolus]. Walcott Te.xt figs. 37A-B, 
 
 p. 408. 
 
 (Paterina) bella [Micromitra], (Billings) II: 1, la-c. 
 
 crenistria [Micromitra], (Walcott) Ill: 4,4a-b. 
 
 etheridgei [Micromitra], (Tate) Ill: 10, lOa-c. 
 
 labradorica [Micromitra], (Billings) LI: 2,2a-L 
 
 labradorica orientalis [Micromitra], (Wal- 
 cott) II: 2. 
 
 labradorica swantonensis [Micromitra], (Wal- 
 cott) II: 3,3a^L 
 
 labradorica utahensis [Micromitra], (Wal- 
 cott) II: 8,8a; 
 
 Text fig. 24, p. 3Sa 
 
 labradorica var. [Micromitra], Walcott Not figiu'ed. 
 
 logani [Micromitra], ( Walcott) II: 6, 6a-b. 
 
 major [Micromitra], (Walcott) Text fig. 25, p. 351. 
 
 phillipsi [Micromitra], ( Iloll) Ill: 8. 
 
 prospectensis [Micromitra], (Walcott) II: 4.4a. 
 
 stissingensis [Micromitra], (Dwight) Ill: 1, la-e. 
 
 stissingensis ora Walcott Not figured. 
 
 stuarti [Micromitra], Walcott Text figs. 26A-B, 
 
 p. 3.55. 
 
 sui)erba [Micromitra] (Walcott) II: 7, 7a-I; 
 
 Text figs. 27A-B, 
 p. 355. 
 
 undosa [Micromitra], (Moberg) Te.xt figs. 28A-C, 
 
 p. 356. 
 
 wapta [Micromitra], Walcott Text figs. 29A-B, 
 
 p. 357. 
 
 williardi [Micromitra], Walcott II; 9b-o; 
 
 Text figs. 30A-E, 
 p. 358. 
 
 pealei [Micromitra], (Walcott) Ill: 3, 3a-e. 
 
 pectenoides [Dicellomus], (Whitfield) Lll: 6, Oa-c; 
 
 Text figs. 48A-B, 
 p. 575. 
 
 peculiaris [Kutorgina], (Tate) V : 2. 
 
 pelias [Obolus mcconnelli], (Walcott) XXIII: 3b-c; 
 
 XXXIX: 5,5a-c. 
 peUico[Xisusia(Jamesella)], (de Verneiiil and Bar- 
 rande) XCVI 1 : 2. 2a-b. 
 
 perattenuala [Lingulella], (Whilfielii) XXI: 1, la-i. 
 
 perfect us(Obolus(Fordinia)], (Walcott) LXIII: 10. lOa-d. 
 
 perpasta [Xisusia (.lamesella)], (Pompeckj) CI: l.la-h. 
 
 perpastamacra[.\isusia(Jamesella)], (Pompeckj) ..CI: 3.3a. 
 perpasta subquadrata [Nisusia (Jamesella)], (Pom- 
 peckj) CI: 2.2a-b. 
 
 penigata [Kutorgina], Walcott V: 3, 3a-€. 
 
 phaon[Lin'.;ulella]. (Walcott) XXVI: l.la-e. 
 
 pheres [Obolus], ^\alcot t XI: 6. Ca-b. 
 
 Philhedra Columbiana ( Walcott) LXXXI; 10. 
 
 phillipsi [Micromitra (Paterina)), (lloIl) Ill: 8. 
 
 pileolus [Orbiculoidea], (Salter) LXXXI; 11, 11a. 
 
 Plectorthis jamcsi (Hall) XC\"I; 5, 5a-c. 
 
 parva (Dalman) XCVI: 6, 6a-g. 
 
 plicatella (Hall) XCVI; 4, 4a; 
 
 Text fig. 12, p. 299. 
 whitfleldi (N. II. Wincheli) XCVI: 3. 
 
INDEX. 
 
 361 
 
 plicatclla [Billingsella], Walcott LXXXVI: 3, 3a-n; 
 
 Text fig. 1, p. 299. 
 plicatella[PleotortliisJ,(Hall) XCVI: 4,4a; 
 
 Text fig. 12, p. 299. 
 
 pogonipensis [LingulellaJ, (Walcott) XX; 3, 3a-c. 
 
 politus (DicellomusI, (Hall) LII; 1, la~k; 2, 2a-i; 
 
 3; 4, 4a; 5, 5a-b; 
 
 Text figs. 16A-B, 
 p.314,and49A-B, 
 p. 576. 
 
 pretiosa [ Acrothele], (Billings) LVIII: 1, la-g. 
 
 pretiosa [Mickwitzia], Walcott VI: 2. 
 
 prima [Acrothele), (Matthew) LXI: 6, 6a-b; 
 
 LXII: 2. 
 
 prima [Acrothyrasignata], Matthew LXXX: 2, 2a-b. 
 
 prima ILiugulellaJ, (Conrad M.S.) (Hall) XXVII; 1, la-c. 
 
 prima costata [Acrothele], (Matthew) LXI; 4, 4a-d. 
 
 primiEva [Acrothele], (de Verneuil and Barrande).-LVII: 6. 
 
 prim8eva[Acrotrcta], Walcott LXIX: 1, la-f. 
 
 primscva [Lingulella?]. Hicks XXXI: 5. 5a. 
 
 priinordialis[Eoorthis], (de Verneuil and Barrande).XCVII: 1, la-d. 
 
 primordialis [Syntrophia], (Whitfield) CII; 2, 2a-e. 
 
 primordialis argia [Syntrophia], Walcott CII; 3. 
 
 prindlei [Obolus], ( Walcott) XXVII: 3, 3a-e. 
 
 priscus[Schizambon]. Matthew LXXXIV: 2, 2a-e. 
 
 pristinus [Trematobolus], (Matthew) LXXXIII: 2, 2a-h; 
 
 LXXXIV: 6. 
 proavia [Acrothyra], (Matthew) LXXV: 3; 
 
 LXXVI: 3, 3a-u. 
 
 proles (Acrothele), Matthew LXII: 3, 3a-c; 4,4a. 
 
 prohflcus [DiccIIomus], Walcott LXXXIX;10,10a-b. 
 
 prospectensis [Micromitra (Paterina)], (Walcott). . .II: 4, 4a. 
 
 Protorthis bilhngsi (Hartt) XCIX: 1, la-g. 
 
 helcna Walcott XCIX: 4, 4a-b. 
 
 ? hunnebergensis Walcott XCV; 5, 5a-c. 
 
 laivis Walcott XCIX: 6, 6a-b. 
 
 latourensis (Matthew) XCIX; 3, 3a-d. 
 
 quacoensis (Matthew) XCIX; 2, 2a-e. 
 
 wingi Walcott XCIII; 5, 5a-c. 
 
 sp. undt. Walcott Not figured. 
 
 Protorthis (Loperia) dugaldensis Walcott XCIX; 5, 5a-j. 
 
 pulchra[Botsfordia), (Matthew) LXII; 5, 5a-l. 
 
 pumila [Lingulella (Lingulepis)], (Matthew) XLV: 3, 3a. 
 
 pimipellyi [Billing.sclla]. Walcott XCVII: 8. 8a-c. 
 
 punctata [Lingulella], (Walcott) XX; 6, 6a. 
 
 pusilla [Micromitra], (Linnarsson) Ill: 2, 2a-c. 
 
 puteis [Acrothele avia], Matthew Not figured. 
 
 pygma;a [Lingulella (Lingulepis)], (Salter) XXX; 10. 
 
 pyxidicula {.\crotreta]. White LXIX; 2, 2a-f; 3, 
 
 3a-f. 
 
 ' quacoensis [Protorthis], (Matthew) XCIX: 2. 2a-e. 
 
 quadrilateralis [Lingulella], (Walcotlj XXXIX: 6, 6a. 
 
 quadrilineata [Acrothele], Pompeckj LVII: 5. 
 
 Quebecia Circe (Billings) CIV: 7, 7a-g. 
 
 quenstedti [Obolus apollinis], (Mickwitz) Text figs. 34A-B, 
 
 p. 374. 
 
 radula [Lingulella], Matthew XLV; 1, Ia-1. 
 
 randomensis [Lingulella], (Walcott) XXI; 5, 5a. 
 
 rara [Acrothele), (Walcott) LXIII: 4, 4a. 
 
 rara [Nisusia], Walcott Text fig. 60, p. 730. 
 
 recurva [ Volborthia), ( Kutorga) I: 6. 6a-e; 
 
 Text figs. 33A-B, 
 p. 36B. 
 (Redlichella) granulata [.\crothele), (Linnarsson). ..LVI: 2,2a-n. 
 
 refulgens [Obolus), Matthew IX: 2, 2a-d. 
 
 remnichafEoorthis], (N. H. Winohell) XCI; l,la-s; 
 
 XCII: 2. 2a-d; 3, 
 3a-e; 
 
 Text fig. 7, p. 299. 
 
 remnicha sulcata [Eoorthis], (Walcott) XCII: 1. la-c. 
 
 remnicha texana [Eoorthis), (Walcott) XCII: 4. 4a-g. 
 
 remnicha winfieldensis [Eoorthis), (Walcott) XCI: 2, 2a-e. 
 
 retrodexa [Billingsella), (Matthew) XC; 1. la-h. 
 
 rhea [Obolus), Walcott IX: 1, la-c. 
 
 richthoteni [Billingsella), Walcott LXXXIX: I. 
 
 roberti [Lingulella (Lingulepis)], (Matthew) XXXVII: 4. 4a-d. 
 
 robusta[Lingulella (Lingulepis) gregwa], (Matthew). Not figured. 
 
 rogersi [Obolus ( Westonia)], (Walcott) XLII: 2, 2a-d. 
 
 rokitzanensis [Obolus?), Barrande XII: 6. 
 
 romingeri [Billinssella], (Barrande) XC: 2,2a-n. 
 
 rotunda [Lingulella] , (Matthew) XXXVII: 3h-k. 
 
 rotundata [Syntrophia], Walcott CIII; 4, 4a-e. 
 
 rotundatus [Obolu.s], (Walcott) XX: 2, 2a-e. 
 
 rowei [Lingulella ( l.ingulopis)], (Walcott) XXI: i, 4a-b. 
 
 rudis [ Acrotreta] , Walcott LX V: 3f; 
 
 LXXV: 1. 
 
 rugatus [Obolus (Acritis?)), Walcott XIII: 2 and 3. 
 
 riigosa [Acrotreta ophirensis], Walcott LXXPV': 2. 2a-e. 
 
 rugosa[Schizopholis), Waagen I: 4c; 
 
 LXXXI; l.la-c. 
 
 rugosicostata [Billingsella exporrecta], Walcott LXXXVIII: 2,2a-c. 
 
 Rustella edsoni Walcott I: 1. la-e. 
 
 ? major (Matthew) Text fig. 19, p. 328. 
 
 sabrinai [Acrotreta], (Callaway) LXXIII: 5, 5a-d. 
 
 saflordi [Wimanella], (Walcott) LXXXVII; 7,7a. 
 
 sagittalis [Acrotreta], (Salter) : LXXI: 2, 2a-h; 3, 
 
 3a-j. 
 
 cf . sagittalis [Acrotreta] Not figHred. 
 
 sagittalis magna [Acrotreta), (Matthew) LX VI: 4. 4a-f. 
 
 sagittalis taconica [Acrotreta), (Walcott) LXXI: l,Ia-o. 
 
 sagittalis transversa [Acrotreta), (Hartt) LXXII: l,la-k. 
 
 salemensis [Billingsella), (Walcott) LXXXVII: 3. 3a. 
 
 saltensis [ Eoorthis), (Kayser) XCVII: 11. 
 
 salteri [Obolus (Broggeria)], (HoU) XIII: l,la-n; 
 
 XV: 4,4a-d. 
 
 sandbergi [Otusia], (N. H. Wincbell) XCIII: 4, 4a-d. 
 
 sardiniaensis [ Kutorgina], Walcott V: 4. 4a-c. 
 
 Schizambon? csthonia Walcott LXXXIV: 4. 
 
 manitouensis Walcott LXXXI\': 3. 3a-e. 
 
 priscus Matthew LXXXIV'; 2. 2a-e. 
 
 typicalis Walcott LXXXIV: l,la-d. 
 
 Schizopholis rugosa Waagen I; 4c: 
 
 LXXXI; l.la-c. 
 
 schmalenseei [Acrotreta], Walcott LXX: 1. la-s. 
 
 schmalenseei [Obolus], (Walcott) XXX; 19. 193-e. 
 
 schinidti [Obolus], Mickwitz XV: lla-c. 
 
 (Schmidtia) acuniinatus [Obolus], Mickwitz XIV; 2. 2a-c. 
 
 celatus [Obolus], ( Volborth) XIV: 1, la-c. 
 
 crassus [Obolu.s), Mickwitz XFV': 4. 4a-d. 
 
 obtusus [Obolus], Mickwitz XIV; 3. 3a-c. 
 
 schucherti [Lingulella], (Walcott) XXI: 6. 
 
 Schuchertina Cambria Walcott LI: 6, 6a-m, 
 
 scotica [Micromitra], Walcott Text figs. 21A-C, 
 
 p. 340. 
 
 sculpt ills [Micromitra], (Meek) Ill: 5, 5a-e. 
 
 sculpt ills cndlichi [Micromitra], Walcott Text fig. 22, p. 342. 
 
 secbachi [Acrotreta], Walcott LXX VII: 3, 3a. 
 
 selwyni [Obolus], (Matthew) XXXVI; 1, la-h; 2, 
 
 2a-b; 
 XXXVII: 1, la-f. 
 
 septalis [Obolus], (Walcott) XXXIV: 2, 2a; 
 
 XXIII: 3d. 
 sequcns (Lingulella (Lingulepis) aciuninata], Wal- 
 cott Text figs. 46A-B, 
 
 p. 551. 
 
 sera [Acrothyra], (Matthew) LXXX: i, 4a-c; 5, 
 
 5a-d; 6, 6a-i; 7, 
 7a-b; 8?. 
 
 shansiensis [Obolus], Walcott XI: 7, 7a-c. 
 
 shantungcnsis [Acrotreta], Walcott LXIX; 5, oa-e. 
 
 shelbyensis [Wimanella], Walcott II: 9, 9a. 
 
 siemiradzkii [Lingulella], (Walcott) XXXI: 2, 2a. 
 
 signalis [Acrotreta], Walcott LXIX: 4. 
 
 signata (Acrothyra], Matthew LXXX: 1, la-d. 
 
 signata [Lingulella], ( Barrande) XXX: 11. 
 
 signata orta [Acrothyra), Matthew LXXX: 3, 3a-b. 
 
 signata prima [.\crothyra], Matthew LXXX: 2, 2a-b. 
 
 siluricus [Obolus (Mickwitzella)]. (Eichwald) XV: 1, la-c. 
 
 similis [Lingulella], (Walcott) XXI:2.2a-j;3,3a-d. 
 
 simplex [Lingulella'?], (Barrande) XXXII: 4, 4a-b. 
 
 simplex [Wimanella], Walcott LXXXIX: 2, 2a-e; 
 
 Text fig. 64, p. 748. 
 
 since [Obolus], (Walcott) XX VI: 2, 2a-h. 
 
 Siphonotreta dubia Walcott LXXXI: 7, 7a-b. 
 
 unguiculata (Eichwald) LXXXI: 6, 6a-e. 
 
 verrucosa (Eichwald) LXXXI: S, 5a-b. 
 
 smithi [Obolus], Walcott Text figs. 38A-B, 
 
 p. 416. 
 
 socialis [Acrotreta], von Seebach...'. LXXIII: 3, 3a-c; 4. 
 
 4a-e. 
 
362 
 
 CAMBRIAN BRACIIIOPODA. 
 
 spatula [LinfruIeUa(Lingiilcpis)], (Walcott) XIX: 5, 5a-b. 
 
 spcncei [Nisusia CJamesella)], (Walcott) XCIIl; 7,7a; 
 
 Textrig.«2, p. 737 
 
 spinosa [Acrotreta], Walcott LXXIX: 4, 4a-g. 
 
 spissus [Obolus (Lingulobolus)], (Billings) XVI: 2, 2a-k; 
 
 XLII: 3, 3a. 
 
 spurri [ Acrothele], Walcott LX : 3, 3a-c. 
 
 squamosa [Lingulella ( Lingulepis 7)], (Hall) XXX: 9. 
 
 starri [Lingulella (Lingulepis)], (Matthew) XXXVII: 2, 2a-b. 
 
 stoneanus [Obolus ( Westonia)], (Whitfield) XXVIII: 2, 2a-g; 
 
 XLIX: 2, 2a. 
 
 stissingensis [Micromitra ( Paterina)], (Dwight) Ill: 1, la-e. 
 
 sti-ssingensis ora Walcott Not figured. 
 
 striata [Billingsella], Walcott LXXXVI: 4, 4a-c. 
 
 stuarti (Micromitra (Paterina)], Walcott Text figs. 26.\-B, 
 
 p. S.W. 
 
 subconica [Acrotreta], Kutorga LXXIII: 2, 2a-i. 
 
 subciiuata [Balmanella], (Conrad) Text fig. 2, p. 299. 
 
 subquadrata [Nisusia (Jamesella) perpasta], (Pom- 
 
 peckj) CI: 2,2a-b. 
 
 subsidua [.Verothele], (White) LX: 1, la-o; 8. 
 
 subsiduahera [.Vcrothele], (Walcott) LX: 9. 
 
 subsidua liT>vis [.Vcrothele], Walcott Not figured. 
 
 sulcata [.Vcrotreta idahoensis], Walcott LX V: 5. 
 
 sulcata [Eoorthis reninicha], (Walcott) XCII: 1, la-c. 
 
 sulcatus [Discinopsis?], Walcott LXXXII: 6. 
 
 superba [Micromitra (Paterina;], (Walcott) II: 7, 7a-f; 
 
 Text figs. 27A-B, 
 p. 355. 
 swantonensis [Micromitra (Paterina) labradorica], 
 
 (Walcott) 11:3, 3a-f. 
 
 Swantonia antiquata (Billings) CIV: 5, 5a-b. 
 
 weeksi Walcott CIV: 0. 
 
 Syntrophia alata Walcott CIII: 3, 3a-d. 
 
 baral>uensis (A. Winchell) CII: 1, la-g. 
 
 calcilera (Billings) CIV: 1, la-i. 
 
 Cambria Walcott Text figs. 72A-D, 
 
 p. 800. 
 
 campbeUi Walcott Text flp. 73A-F, 
 
 p. 801. 
 
 lateralis (Whitfield) CII: 6,0a-g; 
 
 Text fig. 11, p. 299. 
 
 nundina Walcott CII: 4, 4a-<l. 
 
 orthia Walcott CIV: 4, 4a-b. 
 
 primordialis (Whitfield) CII: 2, 2a-e. 
 
 primordialis argia Walcott CII: 3. 
 
 rotimdata Walcott CIII: 4, 4a-e. 
 
 ? unxia Walcott Text fig. 74, p. 805. 
 
 taconica [Acrotreta sagittalis], (Walcott) LXXI: 1, la-o. 
 
 tarpa [Lingulella], (Walcott) XXIII: 2, 2a-c. 
 
 tatei[ Eoorthis]. (Etheridge) : XCVII: 15, 1.5a. 
 
 tennesseensis [ Linnarssonella], Walcott LXXIX: 3, 3a-k. 
 
 tetonensis [.Vcrotreta microscopica], Walcott LXVII: 3, 3a-d. 
 
 tetonensis[ Obolus], Walcott IX: 5, 5a-d. 
 
 tetonensis leda [Obolus], Walcott Not figured. 
 
 tetonensis ninus [Obplus], Walcott VIII: 1 1-lo; 
 
 XI: 1, la-e. 
 
 texana [Eoorthis remnicha], (Walcott) XCII: 4, 4a-g. 
 
 texana [ Iluenella], (Walcott) CIII: 1, la-i. 
 
 texana beviusculus [Iliienolla], (Walcott) Not figured. 
 
 texana [ Lingulella], Walcott X LIX: 3, 3a. 
 
 themis [Obolus (Westonia)], Walcott XI: 2, 2a-c. 
 
 thyone [Eoorthis], Walcott Text figs. 70A-C, 
 
 p. 789. 
 
 torrentis[LingulelIa], (Matthew) XXXV: 7. 
 
 torrentis[Otiolus?], Matthew Not figured. 
 
 transversa [.Vcrotreta sagittalis], (Ilartt) LXXII: 1, la-k. 
 
 transversa[ Linnarssonella], Walcott LXXVIll: 6, 6a-c. 
 
 transversa (Nisusia (est inata], (Walcott) C: 4, 4a-b. 
 
 Trematobolus excelsis Walcott LXXXII: 8, 8a-b. 
 
 insignis Matthew LXXXI V: 5, .'ja-c. 
 
 kempanum (Matthew) LXXXIII: 1, la-o. 
 
 pristinus (Matthew) LXXXIII: 2, 2a-h; 
 
 LXXXIV: 0. 
 
 triangularis[Obolns], Mickwitz Not figured. 
 
 triparilis [ Lingulella], (Matthew) X LV: 2, 2a-f; 
 
 Text figs. 44a-/, 
 p. .537. 
 tullbergi [Eoorthis], (Walcott) XCV: 3. 
 
 tumida [Lingulella], Matthew XXIV: 7,7a-<l. 
 
 turner! (AcrotheleJ, Walcott LX: 7, 7a. 
 
 typicalis[.Schizamtjon], Walcott LXXXIV: 1, la-d. 
 
 ulrichi I Acrotreta], Walcott LXXVIII: 3. 
 
 nndosa [Micromitra (Paterina)], (Mobcrg) Text flgs. 28A-C, 
 
 p. 3S«. 
 
 unguiculata [Siphonotreta], (Eichwald) LXXXI: fi, Ga-e. 
 
 unxia [Syntrophia], Walcott Text fig. 74, p. SOS. 
 
 upis [ Lingulella], (Walcott) XXXVI: 3, 3a. 
 
 uplandica [ .Vcrotreta], Wiman hXK: 3, .'ia-c. 
 
 uplandica lim6ensis[. Vcrotreta], (Wiman) LXX: 4, 4a-c. 
 
 Urania [Linnarssonella], Walcott LXXVIII: 9, 9a-c. 
 
 utabensis [Micromitra (Paterina) labradorica), 
 
 Walcott II: 8, 8a; 
 
 Text ng. 24, p. 350. 
 
 utahensis [Nisusia (Jame.sella)], Walcott CI: 10, 10a. 
 
 utahensis (Otusia], (Walcott) LXXXI.V: 3, Sa-c. 
 
 varians [Orbiculoidea], (Barrande) LXXXI: 8. 
 
 vatiiina (Nisusia ?], (de v'erneuil and Barrande). ..XCVII; 3, 3a-b. 
 
 vermilionensis (Obolclla), Walcott Text figs. 53A-E, 
 
 p. rm. 
 
 vermontana [Iluenella], Walcott Text fig. 711, p. 809. 
 
 verrucosa [Siphonotreta], (Eichwald) LXXXI: 5, .Oa-b. 
 
 viliaboimensis [Acrothelc], Delgado Not figured. 
 
 volborthi [Obolus], Mickwitz Not figured. 
 
 Volborthia recur\'a (Kutorga) I: 6, 6a-e; 
 
 Text flgs. aiA-B, 
 p. 300. 
 
 wanneri (Yorkia), Walcott LXXXII: l,la-i. 
 
 wanniecki (Lingulella], Redlich XXXIX: I, la-n. 
 
 wapta [Micromitra ( Paterina)], Walcott Text figs. 29.\-B, 
 
 p. 357. 
 
 wart hi [Neobolus], Waagen..^. I: 3; 4, 4a-b; 5, 5a; 
 
 LXXXI: 2, 2a-h. 
 Text flgs. 47A-B, 
 p. 507. 
 
 warthi [Wynnia], (Waagen) LXXXIX: 4, 4ar.f; 
 
 Text fig. m, p. 771. 
 
 wasatchensis [Obolus (Westonia)], Walcott XLIX: 5, .5a; 
 
 Te.xt flgs. 41.\-F, 
 p. 407. 
 
 washingtonensis [Yorkia?], Walcott LXXXII: 2, 2a. 
 
 weeksi [Swantonia], Walcott CIV: 0. 
 
 welleri [Lingulella], (Walcott) XXXVIII: 4, 4a-b. 
 
 (Westonia) ilandensis [Obolus), Walcott XLVIII: C, i.a. 
 
 aurora [Obolus], (Hall) XLVI: 1, la-h. 
 
 bait icus (Obolus], Walcott XLVIII: 7, 7a-b. 
 
 blackivelderi (Obolus], Walcott XXXIX: 10, lOa-c. 
 
 bottnicus [Obolus], (Wiman) XLVIII: 4, 4a-c. 
 
 chuarensis [Obolus], (Walcott) XXV: 2, 23-e. 
 
 dartoni [Obolus;], Walcott Text figs. 40A-C, 
 
 p. 455. 
 
 clla [Obolus), (Hall and Whitfield) XXXIII: 3, .3a-c; 
 
 XLVH: 1, la-p. 
 
 ellaonaquiensis[Obohisl, Walcott XLIX: 0, 1'a. 
 
 elongiitus [Obolus], Walcott LXIII: 8. 8a-d. 
 
 escasoni [Obolus], (.Matthew) XLIX: 1, la-f. 
 
 cuglyplms [Obolus], (Walcott) XL.VIII: 1, la-f. 
 
 finlandensis [ObolusJ. Walcott XLVIII: 3, .'ia-b. 
 
 iphis (Obolus], WaJcott XLIX: 4, 4a-d. 
 
 ? hunellosus ((Jbolus 7], ( Barrande) XII: 7, 7a-d. 
 
 notchensis [Obolus], Walcott LXIII: 9. 
 
 rogersi [Obolus], ( Waicott) XLII: 2, 2a-d. 
 
 stoneanus [OImIus], (Whitfield) XXVIII: 2, 2a-g; 
 
 XLIX: 2,2a. 
 
 themis [Obolus], Walcott XI: 2, 2a-c. 
 
 w;isatehensis [Obolus], Walcott XLIX: 5,5a; 
 
 Text figs. 41A-F, 
 p. 4lw. 
 
 wimani [Obolus], Walcott XLVIII: 5, 5o-b. 
 
 whilejivesi [Bicia], Walcott L: 2, 2a-e. 
 
 whitfieldi [ liillingsella), ( Walcott) LXXXVI: S, Sa. 
 
 whitficldi [Plectorthis]. (.N. H. Winchell) XCVI: ,3. 
 
 wichitaensis [Eoorthis], (Walcott) XCI V: 1 , la-o, lu. 
 
 wiehitaensis Iieviusculus lEoorlhis], (Walcott) XCIV': Ip-s. 
 
 williardi [Micromitra (Paterina)], Walcott II: 9b-<'; 
 
 Text figs. 30A-E, 
 p. .m. 
 
 willisi [Obolus], (Walcott) X.XIII: l,la-j. 
 
 Wimanella ? anomala (Walcott) L.XXXVII: 1, la-«. 
 
INDEX. 
 
 363 
 
 Wimanella harlanensis CWalcott) LXXXVII: 5, 5a-d. 
 
 inyoensjs Walcott Text figs. B3A-B, 
 
 p. 747. 
 
 saflordi (Walcott) LXXXVII: 7, 7a. 
 
 shelbyensis Walcott 11 : 9, 9a. 
 
 simplex Walcott LXXXIX: 2, 2a-e; 
 
 Text flg. 64, p. 748. 
 
 ■wlmani [Obolus (Westonia)], WaJcott XLVIII: 5, 5a-b. 
 
 wimani [Eoorthis], (Walcott) XCV: 4,4a-d. 
 
 winfieldensis [Eoorthis remnicha], (Walcott) XCI: 2, 2a-e. 
 
 wingi [Protorthis], Walcott XCIII: 5. 5a-c. 
 
 Winona [Ltngulella], (Hall) X VIII: 3. 3a-b. 
 
 winona convexa [Lingiilella], (Walcott) X^'I1I; 4.4a-d. 
 
 wirrialpensis [Obolella], Etheridge hV: 7.7a-b. 
 
 wirthi [Lingulella], (Barrande) XXX: 7. 
 
 woodwortlii [Acrothele], Walcott LX: 0. 
 
 wortheni [Obolus], Walcott IX: 5e; 
 
 Text flgs. 39A-D, 
 p. 421. 
 
 Wynnia warthi (Waagen) LXXXIX: 4,4a-f: 
 
 Textflg. 68, p. 771. 
 
 yorkensis [Acrothele], Walcott LIX: 4.4a-b. 
 
 Yorkia? miqueli Walcott LXXXII: 4. 
 
 7 orientalis Walcott LXXXII: 3, 3a. 
 
 wanneri Walcott LXXXII: 1, la-i. 
 
 ? washing! onensis Walcott LXXXII: 2,2a. 
 
 zeno [Eoorthis], Walcott Text figs. 7IA-B, 
 
 p. 792. 
 
 zenobia [Micromitro], Walcott Text fig. 23, p. 342. 
 
 zetus [Obolus], (Walcott) XXV: 3..3a-e. 
 
 zeus [Lingulella], Walcott Text fig. 4.5, p. 541. 
 
 zoppi [Obolus?], M'alcott XXX: 16, lOa-b. 
 
 o