The Lower Silurian Ostracoda of Minneso' THE LOWER SILURIAN OSTRACODA OF MINNESOTA. By E. O. ULRICH. [From Vou. I1I OF THE FINAL REPORT OF THE GEOLOGICAL AND NATURAL HISTORY SURVEY OF MINNESOTA.| JULY %, 1894. CHAPTER VII. THE LOWER SILURIAN OSTRACODA OF MINNESOTA. BY EE. O. ULRICH. This order of Crustacea comprises small, generally minute, animals having the entire body enclosed in a shell or carapace consisting of two more or less nearly equal calcareous or corneous valves, united along the back by a membrane, and ‘capable of being opened at their ventral margins. The valves are closed by a sub- central adductor muscle, the attachment of which is marked on their inner sides by a tubercle, a pit or a number of small spots. The body is not segmented but has seven pairs of appendages, of which the first two are antenne, while they, like the others, are also adapted for creeping and swimming. These appendages, together with the caudal extremity of the short abdomen, are protruded along the ventral margin of the carapace when the valves are opened. Behind the first two pairs of appendages (antennules and antenne), is a pair of mandibles, followed by a pair of maxille, while the third‘and fourth pairs may be either legs or jaws. Finally the last two pairs are leg-like and generally stronger than the preceding pairs. The extremity of the abdomen may be bifurcated or con- sist of a single spinous plate. As a rule the eyes are well developed, with commonly a small median and two larger lateral ones present. The position of the latter is often indicated on the exterior of the valves by a small “eye tubercle.” A distinct heart may be present or absent, but the alimentary and generative organs are well developed. The Ostracoda, or “ water-fleas” as they are often called, are represented by very numerous forms both in fresh water and in the sea. Of the families only the Cypride are chiefly fresh-water forms, while most of the other families are restricted to ' marine or brackish waters. Taken as a whole they are to be considered as shallow water inhabitants, and of social habits, being found in great numbers swimming near the surface of the water or creeping over the bottom. Remains of Ostracoda abound [629] 630 THE PALEONTOLOGY OF MINNESOTA. (Ostracoda. also in nearly all the geological formations, and in some cases so numerously that whole layers are almost composed of their shells. The fossil forms are furthermore of great variety, since, with perhaps a single exception, all the families which have been established for the recent forms have also been recognized in the fossil state, while many types occur in the paleozoic rocks that seemingly are now totally extinct. With a single exception (Palwocypris), only the carapace valves are preserved in the fossil condition, and as these are often very similar in different genera and even families, it is evident that their study and classification is a matter of exceptional difficulty. To discriminate between these small fossils the paleontologist is obliged to rely on small differences in the shape, the relative size of the valves, the characters of the edges and of the hinge, the thickness of the valves, and the surface ornamentation. Among the paleozoic forms the valves are commonly lobed or sulcate and variations in these are usually counted important. A frequent difficulty is to distinguish between the anterior and posterior extremities. When not alike, the thickest end (it is generally also the highest) is considered as the poste- rior. It must be confessed, however, that this arbitrary determination can be accepted only as provisional. Some working rule like this is necessary until com- parison of other details of structure will have furnished us with more reliable criteria upon which to base conclusions. The carapace as stated consists of two calcareous or corneous valves of compact structure, commonly less than 4 mm. in length, though in a few cases the length exceeds 20 mm. The two valves may be equal (Tetradella, Primitia, etc.) or more or less unequal, with either the right or left overlapping the other at the ventral border only (Leperditia, Leperditella, etc.), or at the dorsal border as well (Bythocypris and Krausella), while in others the overlap is entire (Cytherella). The hinge or dorsal margin may be straight or arcuate, and, especially among the paleozvic types, is generally simple, though among more recent forms (Cytheride) hinge teeth and corresponding sockets are not uncommonly developed. The anterior and posterior margins may be broadly or narrowly rounded, pointed or drawn out beak-like; and when the back is straight the ends may join it angularly. The ventral margin is oftenest convex though it is not infrequently straight or gently concave. The sides of the valves in the majority of Ostracoda may be said to be approximately even in contour or convexity but in many cases, especially among paleozoic forms, they are indented and thrown into two or more tubercles, lobes or ridges. The surface of the valves may be smooth and polished or it may be granulose, pitted, reticulose, striated, hirsute or otherwise marked, the effect being in many instances quite orna- mental. Finally many of the paleozoic Ostracoda of the family Beyrichiide have a wide, frill-like false border, which projects considerably beyond the true contact OSTRACODA. 631 Ostracoda.] edges of the valves. The genus Eurychilina affords excellent examples of species with a “frill.” As regards the geological or time distribution of the Ostracoda, it is certain that they began in the upper divisions of the Taconic system, if indeed they are not to be reckoned among the earliest fossils known. In the Lower Silurian deposits already they occur in such great numbers and variety, that it is doubtful if the representa- tions of the order at any subsequent time exceeded them in these respects. The predominant types, Leperditiide and Beyrichitde, moreover, while holding their own perhaps through the Upper Silurian, were greatly reduced during Devonian and Carboniferous times and are now totally extinct. Some recent families and genera on the other hand were sparingly represented, but taken as a whole the Silurian Ostracoda fauna is decidedly peculiar.* In the Upper Silurian formations the Leperditiide and Beyrichiide still predom- inated, but the fauna here received decided accessions in the way of genera regarded as belonging to the family Cypride. The Devonian Ostracoda, though less numerous, are not very different from the Upper Silurian types, most of the old genera being more or less sparingly represented. Several genera (¢. g. Kyammodes, Jones, and Barychilina, Ulrich) are so far to be considered as peculiar to this system of rocks. The Ostracoda fauna of the Carboniferous deposits, on the contrary, while retaining many small species of essentially Silurian genera like Leperditia, Beyrichia and Primitia, which occur associated with the related genera Beyrichiella and Beyrichi- opsis and numerous forms of the previously established types of the Cypride, nevertheless assumed a distinctive aspect through the strong development of hitherto unknown types of Cyprinide. In succeeding formations the Ostracoda are everywhere poorly represented in the Triassic and Jurassic. But in the Cretaceous and Tertiary strata of Europe cer- tain genera, Cythere especially, develop an astounding variety and wealth of species. The forms are all small, and this may in part account for the fact that so few have been discovered in American deposits of these ages. The recent genera having, or believed to have, paleozoic representatives, occur in the various formations as follows: Cypridina, Bradycinetus and Philomedes, in the Carboniferous; Polycope, Silurian and Carboniferous; Cytherella and Cythere, Silurian, Carboniferous and Permian; Cythereis and Cytherideis, Permian; Bairdia, Silurian, Devonian, Carboniferous and Permian; Bythocypris, Silurian, Devonian, Carboniferous; Macrocypris, Silurian and Carboniferous; Pontocypris, Silurian; and Aglaia, Argillecia and Candona, in the Carboniferous. *That the Silurian species which are now placed into recent genera actually belong there may well be questioned. In my opinion they do not, yet, as they cannot, with our limited opportunity for comparison, be distinguished, I am obliged to agree that the aims of classification are for the time being sufficiently satisfied. 632 THE PALEONTOLOGY OF MINNESOTA. [Classification of Ostracoda. PROVISIONAL CLASSIFICATION OF THE PALEOZOIC OSTRACODA. ¥amily LEPERDITIIDA. GENERA: Leperditia, Ronault; Leperditella, Ulrich; Isochilina, Jones; Aparchites, Jones; Schmidtella, Ulrich; ? déchmina, Jones. Family BEYRICHITID A. GENERA: Beyrichia, McCoy; Beyrichiella, Jones and Kirkby; Beyrichiopsis, Jones and Kirkby; Kledenia, Jones and Holl; Ulrichia, Jones; Primitia, Jones and Holl; Primitiopsis, Jones; Eurychilina, Ulrich; Dicranella, Ulrich; Halliella, Ulrich; Jonesella, Ulrich; Bollia, Jones and Holl; Cieno- bolbina, Ulrich; Tetradella, Ulrich; Drepanella, Ulrich; Placentula, Jones and Holl; Kirkbya, Jones; Moorea, Jones and Kirkby; Strepula, Jones and Holl; Hocronotellas Ulrich; Primitiella, Ulrich; Dilobella, Ulrich, Family BARYCHILINID A. = GENERA: Barychilina, Ulrich; Kyammodes, Jones. Family ENTOMIDAA. GENERA: Entomis, Jones; Elpe, Barrande; Entomidella, Jones; ? Hippa, Barrande. Family CYPRIDINID 2. GENERA: Cypridina, Milne-Edwards; Cypridinella, Jones; Cypridellina, Jones; Sulcuna, Jones; Cypridella, DeKoninck; Cyprella, DeK.; Bradycinetus, Sars; Philomedes, Lilljeborg; Rhombina, J.; Cyprosis aud Cyprosina, Jones. Family ENTOMOCONCHID &. GENERA: Entomoconchus, McCoy; Offa, Jones. Family POLYCOPID A. GENUS: Polycope, Sars. Family CYTHERELLID A. Genus: Cytherella, Jones aud Bosquet. Family CYTHERIDA. : GENERA: Cythere, Miller; Bythocythere, Sars; Carbonia, Jones; ? Youngia, Jones and Kirkby; Xestoleberis, Sars. Family THLIPSURID AL. GENERA: Thlipsura, Jones and Holl; Phreatura, Jones and Kirkby; Octonaria, Jones. Family CYPRID As. GENERA: Aglaia, Brady; Candona, Baird; Argillecia, Sars; Macrocypris, Brady; Bythocypris Brady; Bair dia, McCoy; Pontos Sars; Pachydomella, Ulrich. Family BEECHERELLIDA, GENERA: Beecherella, Ulrich; Krausella, Ulrich. Family DARWINULIDA. GENUS: “‘Darwinula, Jones (Brady and Robertson). NOT CLASSIFIED. Cytherellina, Jones and Holl; Bursulella and Bernix, Jones; Lepiditia, Lepidilla, Beyrichona and Hipponicharion, Mathews; Isoxys, Walcott, OSTRACODA. 633 Leperditia.] Order OSTRACODA. Family LEPERDILTID. Genus LEPERDITIA, Ronault. Leperditia, RoONAULT, 1851, Bull. Soc. Geol., France, 2d Ser., vol. 8, p. 377; Fr. Scuumrpt, 1873, Mem. Acad. Imp. Set. St. Pétersbure, vol. 21, No. 2; also 1883, idem, vol. 31, No. 5; Jonxys, 1881, Ann. Mag. Nat. Hist., 5th ser., vol. 8, p. 332; Jones and KIRKBY, ‘1887, Proc. Geol. Assoc., val. 9, p. 503. Also JONES, 1856, 1858, 1884, 1890, 1891; KoLMODIN, 1869 and 1879; KRAUSE, 1877 and 1891; Kizsow, 1884; ZIrTEeL, 1885; MrLueEr, 1889; ULRicn, 1890 (not 1892). Previous to 1851 species were referred to Cytherina, Cythere and Cypridina. Carapace more or less convex, often large, suboblong or semiovate in outline, with an oblique backward swing; dorsal edge straight, often angular at the extrem- ities; ventral outline rounded, sometimes a little produced at the middle; greatest thickness in the ventral half, the lower edge usually being also blunt; valves unequal, the right the larger and overlapping the left; overlap chiefly ventral, simple, or the further entrance of the ventral edge of the left valve is prevented by two or more papille set within the overlapping edge of the right; hinge simple. Surface fre- quently horny. in appearance, smooth in most cases, granulose or minutely punctate in others; a small tubercle or “eye-spot” is generally present on the antero-dorsal fourth, and a large, rounded subcentrally situated sunken muscle-spot is seen on the inner side of the valves and not infrequently distinguishable on the exterior also. Type; JL. brittannica Ronault. An excellent account of this genus is given by Dr. Fr. Schmidt (loc. cit.) in his two papers on the “Russichen Silurichen Leperditien.” According to that author and to Roemer, L. grandis Schrenck (L. gigantea Roemer) attained a length of 43 mm. This is the largest species of the genus and probably the largest known ostracode. In most of the species the length varies between 8 mm. and 25 mm., while in several other unquestionably congeneric forms the maximum length is less than 4 mm. Besides, a number of minute forms are referred here by Prof. Jones, myself and others, of which it is at least doubtful that they really belong to the genus. Because of their small size and chiefly perhaps because of the imperfection of the specimens, the ventral overlap of the right valve has not been established for them. Nor has the “eye-tubercle” and other peculiarities of the typical species been seen on them. For some at any rate Aparchites would offer a more natural reception. Finally, a number of comparatively small species (1.5 mm. to 3.0 mm.) which I have here- 634 THE PALEONTOLOGY OF MINNESOTA. [Leperditia fabulites. tofore held as belonging to the genus, are now referred to a new genus on the ground that the free edges of their valves are different and the left instead of the right the larger. . Probably seventy-five good species of the genus are known, the greater number of which and all the larger forms, are restricted to the Lower and Upper Silurian deposits. The earliest forms occur in the Taconic, but it is not till we come to the Trenton that the species become numerous.* The Utica slate and Hudson River group species are nearly all small and of doubtful affinities. The same is true of the Devonian and Carboniferous forms, but in no wise of those which are inclosed in Upper Silurian strata, since in this age the genus seems to have attained its greatest development both in the way of size and species. LEPERDITIA FABULITES Conrad. PLATE XLIII, FIGS. 10—14 Cytherina fabulites CONRAD, 1843, Proc. Acad. Nat. Sci. Phila., vol. i, p. 332. Leperditia fubulites JONES, 1856, Ann. Mag. Nat. Hist., 2d ser., vol. xvii, p. 89; also 1881, idem, 5th ser., vol. viii, p. 342; also 1891, Contri. Can. Micro-Pal, pt. 3, p. 98; Wurr- FIELD, 1883, Rep. Geol. Sur. Wis., vol. i, p. 160; ULRicH, 1890, Jour. Cin. Soc. Nat. Hist., vol. xiii, p. 173. Leperditia canadensis, var. josephiana JONES, 1858, Ann. Mag. Nat. Hist., ser. 3, vol. i, p. 341; also 1858, Geol. Sur. Can., Dec. 3, p. 94. Leperditia fabulites var. josephiana JONES, 1881, Ann. Mag. Nat. Hist., ser. 3, vol. viii, p 344. Leperditia, josephiana JONES, 1884, Ann. Mag. Nat. Hist., ser. 5, vol. xiv, p. 341. S1zzE.—1. Beloit, Wis., {(E.C.) Length, 12.47 Hi; ; hight, 7.9 mm.; thickness, 5.0 mm. 2. Minneapolis (L. V.) ¥ 14.0 ee 8.4 * 8.0‘ 3. oe (R. V.) we Tae st es 1s ee 3.0 ‘ 4, “ (B. C.) " 115 * - 74 6 oe 5.0 * 5. Dixon, Ill. (E. C.) oe 12:2 sy io ue 5.5 6. Lavergne, Tenn. (L. V.) n 13.2 " a 8.3 ‘ i 31 7. Lebanon, Tenn. (E. (.) 10.0 “ = 6.5 * ef cy 8. oe (KE. C.) oe 1.5 $e te 4.7 a ch 3.2 it3 9. ue (I. C.) + 82. Hs 5.2 Hf 3.8 10. ss (E. C.) a 7.0 ‘ 8 47 8 fe 33 06«(S 11. ss (E. C.) 8.0 * se 5.0 ‘* Carapace of medium size, obliquely subovate, comparatively long, widest poste- riorly; ventral curves moderate, strongest just behind the midlength; cardinal line straight, comparing with the length of the valve as 2 is to 3, the two extremities almost equally angular; hight of ends about as 3 is to 4, both obliqely truncate above, the anterior narrowly rounded in the middle; the posterior outline more broadly and evenly curved though having the usual backward swing. Ventral edge of carapace obtuse, scarcely flattened, with a slight furrow on each side near the edge of the *Considering that the equivalent strata of Kentucky, Tennessee and Canada, contains no less than eleven species of Leperditia, it is a little remarkable that only one undoubted species of the genus has so far been discovered in the Trenton series of strata of the northwestern states, +1n giving the size of specimens, their condition is indicated by the abbreviations E. C., R. V., and L. V., signifying, respectively, entire carapace, right valve, and left valve. Where these initials are not used, it is to be understood that the dimensions are of an entire carapace, OSTRACODA. 635 Leperditia fabulites.] right valve in which a row of minute puncte is generally distinguishable; overlap extending all around the free edges, strongest ventrally; except in rare instances, neither valve has a flange or flattened border, and when present it isin all cases very narrow and undefined; dorsal edge somewhat thickened, especially upon the left side. Surface of valves smooth or very faintly pitted, rather evenly convex with the greatest thickness somewhat beneath the center; a low ridge-like thicken- ing along the posterior half of the dorsal margin of the left valve is to be noticed. Kye tubercle just distinguishable in most cases, rarely so distinct as in the specimen figured, often not to be detected. On the inner surface however it is always marked by a distinct pit. Muscle spot not distinguishable externally except when the specimens are weathered, but on the inner side it is often well marked and surrounded by fine reticulating radial lines, short dorsally, longest post-ventrally. On the inner side of the ventral edge of the right valve there are two rows of small papilla, three to five in each, the number seeming to increase with age. The purpose of these papilla, one series of which occurs in the anterior third, the other in the pos- terior, evidently was to prevent undue overlapping of the valves by presenting an obstacle to the entering ventral edge of the left valve. Of this species, I have before me no less than five hundred specimens, represent- ing twelve localities in the states of Minnesota, Wisconsin, Illinois, Kentucky’ and _ Tennessee. Considering its wide geographical range and abundance, it is remarka- bly constant in all its characters. That it is so in its outer form is clearly enough shown by the above measurements, taken from representative examples. They show further that the northwestern Specimens are on an average about one-third larger than those from Tennessee. In all other respects however they are all practically identical. Tn 1890 (loc. cit.) I believed it probable that L. josephiana Jones, would prove distinct from L. fabulites, but it is now quite evident to me, as it also has become.to Prof. Jones, that there is no ground whatever for any distinction between them. Compared with other species, the Upper Silurian L. hisingert Schmidt, is not far removed, and the variety fabulina from Lake Winnipegosis very similar indeed. Still as pointed out by Prof. Jones there are a number of minor differences between them, and these will no doubt be added to when the later form is fully known. Another closely related form is the L. wiluiensis Schmidt, from the Upper Silurian of Russia. Its hinge line is shorter and the antero-ventral curve somewhat fuller, but in other respects, even to the rows of puncte along the ventral margin, the two species are muchalike. L. linneyi Ulrich fromthe Upper Trenton of Kentucky is more obliquely produced posteriorly and has a shorter hinge line, a flatter ventral edge, distinct flanges, and better developed tubercle and muscle spot. 636 THE PALEONTOLOGY OF MINNESOTA. [Leperditella. Formation and locality.—Lower Trenton or Birdseye limestone, Minneapolis, St. Paul and Cannon Falls, Minnesota; Mineral Point, Janesville and Beloit, Wisconsin; Rockton and Dixon, Illinois; High Bridge and Frankfort, Kentucky; Lebanon, Lavergne and Murfreesboro, Tennessee; also St. Joseph Island, Lake Huron, and Murray Bay, Canada. It is said to occur in a similar position also in New York. Genus LEPERDITELLA, n. gen. . od Leperditia (part.) ULRICH, 1892, Amer. Geol., vol. x, pp. 263-268. Carapace leperditoid, ovate or oblong, with a straight back; surface of valves without eye tubercle or distinguishable muscle spot, but a more or less obscure broad depression is generally present in the central part of the dorsal half; left valve a little larger than the other, the free edges of the latter fitting into a groove. Length 1 to 3 mm. Type: Leperditia inflata Ulrich (not L. inflata Murchison sp.). Fig. 46. a, small left valve of Leperditella influta Ulrich; b, inner side of a larger valve of same, show- ing the marginal groove; c, vertical section in outline of entire carapace of same; d, dorsal outline of left valve of same; ¢ and f, external and internal views of a left valve of Leperditella mundula Ulrich; g and h, outlines in anterior and ventral views of same; i, right side of an entire carapace of Leperditella wquila- tera Ulrich; j, right valve of Leperditella sulcatu Ulrich; k, left valve of L. sulcata var. ventricornis Ulrich. All the figures are magnified 10 diameters, and all the specimens from either the upper or the lower beds of the Birdseye limestone at High Bridge, Kentucky. This genus is separated from typical Silurian Leperditia because the left instead of the right valve overlaps the other, and instead of a simple overlap the ventral edge of the right valve fits into a groove in the left. Furthermore, the eye tubercle and muscle spot of Leperditia are not distinguishable externally in Leperditella. In certain Carboniferous species of Leperditia (L. carbonaria Hall, L. nicklesi Ulrich and others) the overlap of the valves, though reversed, is very similar to that of the Lower Silurian species here brought together as Leperditella. Perhaps they also ought to be distinguished from Leperditia, — : Leperditella embraces L. tumida, L. mundula, L. equilatera, L. inflata, L. germana, L. sulcata, and var. ventricornis and L. ? dorsicornis, all described by me in the Amer- ican Geologist for November, 1892, as species of Leperditia. To these I now add L. canalis, L. persimilis and L. macra. With the exception of L, ? dorsicornis, which is from the Hudson River group. all these species occur in strata equivalent to the Birdseye and Black River limestones of New York. OSTRACODA. 637 Leperditella canalis.] Prof. T. Rupert Jones recently described two species from Canada (Contri. Can. Micro-Pal., pt. 8, 1891), that may be congeneric with these species, viz.: Leperditia ? obscura and Isochilina labellosa, the latter appearing to be much like LD. tumida. LEPERDITELLA CANALIS, ”. Sp. PLATE XLITI, FIGS. 1—3. Size.—Length, 1.78 mm.; hight, 1.22 mm.; thickness (L. V.) 0.59 mm. Carapace ovate, widest posteriorly, tumid, the point of greatest thickness but little behind and beneath the center; anterior outline semicircular; dorsum straight, not angular in front, and quite obtuse behind, posterior margin somewhat obliquely rounded, scarcely truncated above; near the ventral edge of the !eft valve a distinct channel or groove, deepest centrally, has suggested the name. Surface smooth. This species is closely related to L. tumida Ulrich, occupying a similar geological position in Kentucky and Tennessee, and of which a right valve is figured for com- parison on plate 45, (figs. 13—15), The outline in that species however is not so regularly rounded in front, nor so full antero-ventrally, the greatest convexity is more posterior and scarcely so great, and the dorsal angles more distinct. But the feature particularly relied on in distinguishing the two species is the groove along the ventral border of the left valve in L. canalis, the Kentucky form being without this peculiarity. . Formation and locality.—Lower limestone of the Trenton formation, Minneapolis, Minnesota. LEPERDITELLA PERSIMILIS, #%. Sp. PLATE XLII), FIGS4—6, Size.—(E. C.) Length 1.75 mm.; hight 1.23 mm.; thickness 0.8 mm. Carapace ovate, moderately convex, with the ends nearly equal; no dorsal angle behind but a well marked one in front; ventral overlap distinct; dorsal edge thick, shoulder like; greatest thickness central; suface smooth. The length varies between 1.5 mm. and 2.5 mm. At first sight this species looks very much like L. canalis, but carefully compared they prove quite distinct. The outline is somewhat different being less wide (high) posteriorly, the dorsal angles are reversed, and the dorsal edges much thicker, while the thickness of the carapace is less and the ventral groove, which marks the left valve in that species, wanting: Similar differences distinguish it from L. tumida. Aparchites ellipticus holds about the same size and is not very different in outline. Still as its valves do not overlap ventrally and as it has no dorsal angles and really 638, THE PALEONTOLOGY OF MINNESOTA. [Leperditella macra. is a very distinct species, there is probably not much danger of confusion between them. Formation and locality.—Middle third of the Trenton shales, Minneapolis, Minnesota. LEPERDITELLA MACRA, 2. Sp. PLATE XLIII, FIGS. 7-9. SizzE.—.E. C.) Length 1.4 mm., hight 1.08 mm.; thickness 0.55 mm. Carapace short, scarcely oblique, subovate; dorsal margin straight, four-fifths of entire length of carapace, angles distinct; ends subequal, rounding almost uniformly into the basal outline; carapace moderately convex except in the anterior third, which is strongly compressed, giving a very unusual ventral and dorsal profile; anterior edges thickened, ventral overlap strong; surface smooth. This species is remarkable for its compressed anterior part, and for its short form, in neither of which features it is equalled by any leperditoid ostracode known to me. Formation and locality.—Middle third of the Trenton shales, Minneapolis, Minnesota. LEPERDITELLA GERMANA Ulrich. PLATE XLV, FIGS. 24—26. Leperditia germana ULRICH, 1892, American Geologist, vol. x, p. 266. Sizz.—(L. V.) Length 2.17 mm.; hight 1.4 mm.; thickness 0.67 mm. Carapace subovate, ends nearly equal, the posterior somewhat the wider; back straight for about four-fifths of the entire length, dorsal angles well marked; ventral outline somewhat oblique, most prominent just behind the center; edges rather blunt, with a narrow groove or rim along the free margins of the left and perhaps of both valves. Surface with the greatest convexity in the posterior half, and a broad, undefined depression in front of the center of the dorsal slope. This form is closely related to L. mundula and L. inflata, two species from the lower division of the Birdseye limestone in Kentucky. From the first it differs in having the ends more equal, the edges blunter, and the surface more convex in the dorsal half. The narrow marginal rim is wanting in that species, and instead of a simple dorsal depression, that form has a low elevation in the lower part of it. The second differs chiefly in the greater inflation of the posterior half of its dorsal region. Formation and locality.—This species has so far been met with only in the Lower Blue Jimestone of the Trenton at Mineral Point, Wisconsin, and Dixon, Illinois, but we know of no reason why it should not occur also at Minneapolis and other localities in the state. OSTRACODA. 639 Leperditella dorsicornis ] LEPERDITELLA ? pDorsicornis Ulrich. PLATE XLV, FIGS. 19, 20 and 20a. Leperditia ? (Primitia) dorsicornis ULRICH, 1892. American Geologist, vol. x, p. 267. Sizz,.—(L. V.) Length 1.72 mm.; hight 1.1 mm.; thickness 0.54 mm. Valves subelliptical, slightly oblique, the ends subequal, the back straight nearly to the- posterior extremity; the latter is generally convex and almost vertical in the upper two-thirds, while in the lower third the outline merges rapidly into the uni- formly convex basal margin; anterior end uniformly curved. Surface much the highest in the posterior half, with a part prolonged dorsally into a short and obtusely pointed prominence that bends down close to the hinge line and projects somewhat beyond it. This prominence gives definition to the posterior side of a distinct sulcus extending almost half across the valve from the central part of the dorsal edge, and forward along the latter. Though having a sulcus, and therefore agreeing in a general way with Primitia, I have chosen to arrange this species with Leperditella because it seems to represent merely an extreme development from such typical species of the genus as L. inflata, L. germana aud L, suleata. Specifically the present form is readily enough distin- guished by the concentration of the dorsal prominence, and greater definition of the sulcus. The form which I called Primitia glabra,* and which occurs in the upper beds of the Cincinnati group in Ohio and Indiana, has a similar outline, but it is somewhat smaller and without the dorsal prominence. Still, I would not be sur- prised to find that it has overlapping valves as in Leperditella. Formation and locality.—The type was found in the Hudson River shales at Savannah, Illinois. As equivalent strata occur near Wykoff and Spring Valley, Minnesota, it is quite likely that the species occurs also in this state. Genus SCHMIDTELLA Ulrich. Schmidtella, ULRICH, 1892. American Geologist, vol. x, p. 269. Carapace small (2 mm. or less in length), short, rounded or subovate, moderately convex, more or less inflated in the dorsal region, this part being the thickest and appearing generally (in an end view), as projecting shoulder-like over and out from the straight hinge line; right valve slightly larger than the left and overlapping it along the ventral margin. No eye tubercle nor sulcus, but a faint central pit and elevation occasionally present. Type; SS. crassimarginata, Ulrich. * Jour. Cin. Soc. Nat. Hist., vol. xiii, p, 134; 1890. 640 THE PALEONTOLOGY OF MINNESOTA. [Schmidtella crassimarginata. The species which I propose to arrange under this genus might have been placed with Aparchites, Jones, were it not that they have overlapping valves. Even without that difference it may be questioned if such an arrangement would have been strictly proper, since no true Aparchites is strongly developed or gibbous in the dorsal region. As a rule Aparchites is thickest beneath the middle of the valves. The same is true of Leperditia, a genus that will, I think, be admitted by all to be distinct from Schmidtella. Though still somewhat in doubt respecting the systematic position of the new genus, it seems well to place it provisionally between Leperditia and Aparchites. Besides the six Trenton species about to be described, Schmidtella will include Aparchites ? obsoletus and A. oblongus of the Upper Silurian rocks of Europe. I refer to the specimens so designated and identified by Dr. Krause* with two British species described by Jones and Holl under Primitia in 1865, and more recently (1889) referred to Aparchites by Prof. Jones. While I am inclined to question the identity of the British and German specimens, I can scarcely doubt that the latter at least are truly referable to Schmidtella. ScHMIDTELLA CRASSIMARGINATA Ulrich. PLATE XLIIJI, FIGS. 42—44. Schmidtella crassimarginata, ULRIcH, 1892, Amer. Geol., vol. x, p. 269. Sizz.—(R. V.) Length 1.80 mm.; hight 1.45 mm.; thickness 0.607 mm. Valves broadly suboval, very slightly oblique, the dorsal outline more gently arcuate than elsewhere, ends nearly equal though the posterior margin is more curved, especially above, than the anterior, the latter often forming an obtuse angle where it joins the dorsal line; ventral outline uniformly curved, semielliptical; back flattened, slightly convex in a side view, raising very abruptly from and projecting slightly above the nearly straight hinge-line; point of greatest thickness just behind the center of the upper half; a rather conspicuous yet not sharply defined broad furrow around the ends and ventral margin, least distinct posteriorly, produces the thick border that has suggested the specific name. Specimens vary in length from 1.6 mm. to 2.0 mm. The border is more distinct and wider, and the back more flattened than in any of the other species referred to the genus. Formation and locality.—Lower Trenton limestone, Mineral Point, Wisconsin, and Dixon, Illinois. Its occurrence in this limestone at Minneapolis is not yet established with certainty. *Zeitschr. d, Deutsch. geolog. Gesellschaft,1891, p. 492. +The dimensions given in the original description are too small, the magnification of the valve measured having been supposed to be 15 diameters when it was only about 10 diameters. OSTRACODA. 641 Schmidtella affinis.] ScHMIDTELLA AFFINIS, 7. sp. PLATE XLII, FIGS. 45-47. SizE.—(R. V.) Length 0.97 mm.; hight 0.72 mm.; thickness 0.22 mm. The largest valve seen has a length of 1.08 mm. and a hight of 0.9 mm. This species is closely related to S. crassimarginata, and at first I was inclined to view it as a later variety of that species. But, considering the great constancy which prevails among the hundreds of valves of S. crassimarginata which I have seen, and the equal constancy exhibited by S. affinis, it has been thought best to hold- them as distinct. Besides I found it difficult to decide to which of the two, S. crassi- marginata or S. umbonata, the present form bore the greater resemblance. Compared with the first of these species, S. affinis is smaller, a trifle higher, the flat dorsum narrower, the ends less equal, with the posterior extremity more strongly curved and the basal outline more prominent in the middle. In an end view the profile is less triangular and the ventral edge thinner. The most prominent point of the surface also is more posterior, while the broad border, which is so conspicuous a feature for S.crassimarginata, is scarcely developed. For comparison with S. um- bonata and S. incompta, see following descriptions. Formation and locality.—Galena shales, near Cannon Falls, Minnesota. ScCHMIDTELLA UMBONATA, %. SD. PLATE XLV, FIGS. 36—38. SizzE.—(L. V.) Length 0.8 mm.; hight 0.59 mm.; thickness 0.23 mm. (R. V.) 6c 0.8 et acs 0.65 te ce 0.23 “ Valves ovate, slightly oblique, ends subequal, dorsum umbonate, projecting considerably above the straight hinge line; free margin with a border, narrower and less distinct on the left valve than on the right; greatest convexity near the middle of the valves, the point occasionally marked by a very faint depression or discolored spot. This abundant species is relatively longer than S. affinis, has more nearly equal ends, narrower and better defined border, and more uniformly convex valves. From the much larger 9. crassimarginata it differs too obviously to require comparison. S. subrotunda may be closely related but is much shorter and almost round. Formation and locality..—Upper third of the Trenton shales, St. Paul and Cannon Falls, Minnesota. A variety, oc more likely a closely related species, occurs in great numbers on slabs of Birdseye limestone collected at High Bridge, Kentucky. 41— 642 ‘THE PALEONTOLOGY OF MINNESOTA. [Schmidtelia incompta. SCHMIDTELLA INCOMPTA, 2. Sp. PLATE XLII, FIGS. 39-41. PLATE XLV. FIGS. 27, 32 and 33. Size.—(R. V.) Length 1.1 mm.; hight 0.8 mm.; thickness 0.28 mm. “0.9 ‘f «0.65 0.18 “ var. subequalis. Valves moderately convex, dorsal margin straight, about half as long as the valve; ends nearly or quite equal, ventral outline regularly curved; surface highest a little above and behind the center, the dorsal slope convex but not projecting beyond the hinge line, the ventral slope long, gentle and straight or faintly concave, the wide border being almost obsolete. Of this species we have two varieties, one occurring in the lower part of the Trenton shales, the other in the upper part of the Galena shales. The earlier or typical form (plate XLV, figs. 27, 32 and 38), is a trifle more convex and blunter at the dorsal edge, slightly shorter and less equilateral than the other. That the Galena variety constantly developed these minute peculiarities is shown by about fifty valves. Should a subordinate name be desirable, it might be called var. subeequalis. ' The dorsum is less tumid in this species than in any of the preceding. On the whole it may be considered as marking an approach toward Aparchites. Still, the prominence of the surface in the post-dorsal third, though not strong, indicates a relation to S. affinis. A species occurs in the Birdseye at High Bridge, Kentucky, that seems to be intermediate between this species and S. wmbonata. Formation and locality.—Typical form, lower part of the Trenton shales, Fountain, Minnesota; var. subeequalis, upper part of the Galena shales near Cannon Falls, Minnesota. ScHMIDTELLA BREVIS, 7. sp.: PLATE XLV, FIGS, 34 and 35. Sizz.—(L. V.) Length 0.8 mm.; hight 0.65 mm.; thickness 0.2 mm. Valves short, subovate, the oval being formed by drawing out the anterior end; dorsum short, gently arcuate, and projecting slightly above the straight hinge line; border inconspicuous. . In most respects this species is much like its associate, S. incompta, but the valves are much shorter, the dorsal outline is not straight, and the anterior margin is more narrowly rounded. Polycope sublenticularis Jones, from the Anticosti group, has a similar outline, but seems to be uniformly convex which is not the case with the species under consideration. Formation and locality.—Rare in the lower part of the Trenton shales near Fountain, Minnesota. OSTRACODA. 643 Schmidtella subrotunda.] SCHMIDTELLA SUBROTUNDA, 2. Sp. PLATE XLV, FIGS. 39—42. Sizz.—Length 0.5 mm.; hight 0.43 mm.; thickness 0.3 mm. Valves small, short, rounded-ovate, rather uniformly convex, with an obscurely defined, narrow.border around the ends and ventral margin; near the center a faint depression, and immediately behind it a small elevation. The generic position of this small species is uncertain. It is placed under Schmidtella chiefly because it seems to be related to S. umbonata, though much shorter. Its outline is almost exactly as in the Cytherella? subrotunda of this report, which was also found associated with it. Possibly they belong to one species. Still, as the type of the Cytherella has neither a central pit nora border, J am for the present obliged to regard them as distinct. Formation and locality—Lower third of the Trenton shales, Minneapolis, Minnesota. Genus APARCHITES, Jones. Aparchites, JONES, 1889. Ann. and Mag. Nat. Hist., ser. 6, vol. iii, p. 385. Carapace subovate, oblong, or somewhat rounded, with a straight hinge of ‘variable length; valves subequal; edges thickened, never overlapping, often beveled or chaneled, in other cases simple, and rarely with a narrow flattened border. Surface more or less convex, usually smooth, without sulcus, tubercles or lobes. Type: OM ©, 0950 38 25808) ap. Cano Fig. Fig. Figs. Figs. Figs. Figs. Figs. . Figs. Fig. Figs. Fig. Figs. Figs. ~ 3 and ~ 4a. 5 to 7 6and 7. 8 to 11. 8and 9. 10 and 11. 12 to 16. 12 to 14, 15 to 16. 17 to 19. 20 to 22. 20 and 21. 22, 9 ade 24 and 25. 26. 27 and 28. 29 to 35. 29 to 3l. 32, 33. 34 and 35. PLATE XLIV. ~ All the figures on this plate are magnified about twenty diameters. TEURYCHILINA RETICULATA ULYPich.......... 0c cece ee ccc eee cence ee seeeceeateeees 660 A perfect left valve of this species. Lower third of the Trenton shaies, Fillmore county, Minnesota. EURYCHILINA RETICULATA, Var. INCURVA, D. VAI... cece eee cece eee cc en nent eeenee 660 Left valve from the upper third of the Trenton shales at St. Paul, Minnesota. EURYCHILINA SUBRADIATA UITrich..........cccce cece cece ee cent eee ee ene een eee sees 661 Interior of a perfect right valve. Nearly perfect left valve, showing the usual characters of the species as it occurs in Minnesota. Section of same across central portion of valve. Lower third of the Trenton shales, Minneapolis, Minn. EURYCHILINA (?) SYMMETRICA, D. SD... . 6.5 cece cece cece tener eee eee teen eeeneeneens 663 (See also plate XLV, figs. 4—6.) Interior of a right valve. Exterior and anterior views of a more elongate left (?) valve. Upper third of the Trenton shales, St. Paul, Minn. CTENOBOLBINA, FULCRATA, Ds SPisscasceveceas sesdevecaacrssceievecsnseceeueeue eas ~ 674 Lateral and posterior views ofa left valve, presenting the usual characters of the species. Lateral and dorsal views of a right valve, resembling in certain respects the next species. Upper third of the Trenton shales, St. Paul, Minnesota. CTENOBOLBINA. GRASSA, UIPICH 6 oeis-ccssis's essa iainiersinteara.s ernie eisitinie aisiale Daisy epg te eeurwe 675 Lateral, posterior, and dorsal views of aleft valve. This is the original type ~ * of the species. Upper third of the Trenton shales, St Paul, Minnesota. _ Lateral and posterior views of another left valve from the same locality, differ- ing in several respects from the type. JONESELLA OBSCURA, I. SD.........000s mania Gu iea guauit Oh balelum ebiwia Montene mes 668 Left and right valves and an interior view of the first. The ‘‘ horseshoe” ridge is very obscure in its lower curved part. Galena shales, Cannon Falls, Minn. DREPANELLA BIGENERIS; Dis SPs sans oes ea ssea dec eee ee nae eae we cee ies ewes ealeee'e 672 Side and posterior views ofa left valve. Lower Trenton limestone, Minneapolis, Minnesota. Longitudinal sectional view across the central part of the same. DICRANELLA SPINOSA, D. SP... 0. eee eee eee eens seston spain meaner 665 (See also plate xLvI, fig. 41.) A left valve of this species. Middle third of the Trenton shales, Minneapolis, Minnesota. DICRANELLA (?) SIMPLEX, 1, SP.... cece cece cece cece ee cece tena ce eeen ener eeeeeeeees 666 (See also plate xLvI, fig, 42.) Lateral and posterior views of a left valve. Galena shales, Cannon Falls, Minn. In fig. 24 the oblique spine on the left side of the center appears scarcely prominent enough. DICRANELLA BICORNIS, D. eM, Cb SP... . cee e cece cece eect eee e eens eeenenereeee 665 (See also plate xLvI, figs. 39 and 40,) A right valve wanting only the posterior part of the marginal frill. Middle third of the Trenton shales, Minneapoiis, Minnesota. DICRANELLA MARGINATA, DL SP... ce cece eee e cece eee nee nent nee ne tener e ee nees 666 Lateral and posterior views of a right valve. Trenton shales, near Fountain, Minnesota. BYTHOCYPRIS OYLINDRICA Hall, SP. .... cece cece eect eee ee eect eee ene eeeneeees 687 The left side, dorsal, and posterior views of an average example of this species. Lower beds of the Cincinnati group, Cincinnati, Ohio. View of the interior of a right valve, showing a slight central thickening of the test. From the same locality. - Ventral view of a complete carapace; also from Cincinnati, Ohio. Lateral and dorsal views of a small right valve, which is also a little narrower than usual. Galena shales, Cannon Falls, Minn. [OvER. Figs. Figs. Fig. Figs. Figs. 36 to 39 to 40 to 44 to 47 to 47 to 38. 42. 39. 42. 43. 46. 53. 49, 50. . 51 and 52. 53. PLATE XLIV. — Continued. BYDHOOCYERIS (2) LCURTA, TBD)... «vacua ccssccisnsin snus oiniee ieee our eb leieagaue Qimnnalwneewe __ Lateral, ventral, and anterior views of a rather small specimen. Middle third of the Trenton shales, St. Paul, Minnesota. BYTHOCYPRIS GRANTH, DY8Dis: «dias cewawornaneewedusicengs sede eee ral ereaw enews A large left valve. Middle third of the Trenton shales, St. Paul,. Minnesota. Lateral, anterior and ventral views of a smaller right valve, from the same locality. CYTHERELLA (?) SUBROTUNDA, D. SP...e. esc ceee cen e eee recs ann eesneeetneenee tens The left side of the complete carapace upon which the species is founded. Lower third of the Trenton shales, Minneapolis, Minnesota... KRAUSELLA INZQUALIS, 0. gen. et Sp...... Pe Ce ee Three views of an entire carapace. Lower Trenton limestone, Dixon, Illinois. KRAUSELLA, ARCUATA; Di SDs ..cdsiscescad cane terse cdGnssaseneeneer Sea sev eee seany Three views of the smaller (right) valve. Birdseye limestone, High Bridge, Kentucky. Relatively higher than the northwestern specimens. Right valve from the lower third of the Trenton shales at Minneapolis, Minn. Lateral and ventral views of another right valve. Lower Trenton limestone, Mineral Point, Wisconsin. View of the interior of a left valve. Also a vertical section through center of same. High Bridge, Kentucky. 689 685 692 692 CUO DETBAND ar MATT R AD GOSHRDEDT SUV OF MIN TISOA Vol. Il. Ostracoda] Plate XLIV. Figs. Figs. Figs. Figs. Figs. Figs. Figs. Figs. Figs. Figs. Fig. Figs. Trigs. Figs. Figs. PLATE XLV. Unless otherwise 1s stated, all the figures on this plate are magnified about twenty diameters. 1 to 3. EURYCHILINA VENTROSA, D SD.-OF VaP...... cece cece cece cece ee eteacenceeecees 1. Left valve, imperfect at the extremities, yet preserving the essential characters of the species. Galena shales, Cannon Falls, Minnesota. 2and 3. Lateral and posterior views of a perfect right valve, from the same locality. 4 to 6. EURYCHILINA (?) SYMMETRICA, D.SD........ ccc cece cece cece ence ce neeaveuseeavas (See also plate XLIv, figs. 5—7.) 4and 5. Side and end views of a valve. x 28, differing somewhat from the specimens figured on plate XLIV. Upper third of the Trenton shales, St. Paul, Minn. Longitudinal section of same. > 7 to © EURYCHILINA (?) SUBASQUATA, TL. SD... ec. cece cece cece ee cece cece eetecenceaeeneees Side view ofa left valve, with vertical and longitudinal sections ofsame. Upper a third of the Trenton shales, St. Paul, Minnesota. 10 to 12. APARCHITES FIMBRIATUS UIrich.. 1.2... 0... cece cc cece cect ee cece eens nee eneneens Side, ventral and posterior views of aright valve. Hudson River group, Spring Valley, Minnesota. 13 to 15. LEPERDITELLA TUMIDA Ulrich............. cece ccc cece cece erence ents eeeneeeaes Side, dorsal, and posterior views of a typical right valve of this species, x 15, from ' the Birdseye limestone at High Bridge, Kentucky. Introduced for comparison with L. canalis and L. persimilis, figured on plate XLIII. 16 to 18. APARCHITES MILLEPUNCTATUS Ulrich.. ........ 0... cee cece cece ee nee cone eeceeeee Ventral, anterior, and side views of aright valve. Surface punctation omitted except on the antero-dorsal fourth of fig. 18. Trenton shales, Fountain, Minn. 19 and 20. LEPERDITELLA DORSICORNIS Ulrich............... 0 ce ceeeeeeees Caiuittos Wiave'ee\ oie ww areweiare 19. A left valve, x 15. Hudson River group, Savannah, Illinois. 20 and 20a. Outlines of same in dorsal and anterior views. 21 to 23. APARCHITES GRANILABIATA ULFiCh..... 1... eee cee cee cece cece cence eee nee eteeee Posterior, side, and ventral views of a left valve. The minute surface granules are omitted except on a small space of fig. 22. Upper third of the Trenton shales, St. Paul, Minnesota. 24 to 26. LEPERDITELLA GERMANA UITrich........ cece cece eee cence renee en eeee ee enees as Outlines of a left valve in anterior, side, and ventral views, x 15. Lower Tren- ton limestone, Mineral Point, Wisconsin. 28 to 30. PRIMITIELLA FILLMORENSIS, De SPewesivswunawwsoeveesiaceevadentea eases aa3s nasa eee Three views of aright valve ofthis small species. Trenton shales, Fountain, Minnesota. 31, PRIMITEA MEIN UTISSIMA, Ti SP wiwisicwecouiet es i. anen eabGuaneiew aaa hee seth eee eb eebins A left valve. Trenton shales, Fountain, Minnesota. 27, 32—33. SCHMIDTELLA INCOMPTA, D. SP. .ee. cece eee e cece eee ete tne cee eee n eee teneteas (See also plate xumzJ, figs. 39—41.) 27. Interior of a left valve. Trenton shales, Fountain, Minnesota. 32 and 33. Side and anterior views of a right valve; from the same locality. 834 and 35. SCHMIDTELLA BREVIS, D. SP........ cee cece ce cece ce cece ce eer ee eee teeter teen teenes Side and anterior views of a left valve. Trenton shales, Fountain, Minnesota. 36 to 38. SCHMIDTELLA UMBONATA, D. Sp........-. Vaaewesiieee ut Wekaere vedi aaidars 36 and 37. Anterior and side views of a left valve (opposite valve restored). Upper third of Trenton shales, St. Paul, Minnesota. 38. View of the interior of a right valve, from the same locality. 39 to 42. SCHMIDTELLA SUBROTUNDA, I. SD........ Sh bpsila Laake eRe oe onal de nenteia mous Side and end views of a right and left valve. In both cases the opposite valve has been restored. Lower third of the Trenton shales, Minneapolis, Minn. PAGE. 662 663 663 645 637 645 639 644 638 649 651 642 642 641 643 TSR SURVEY OF MENESUEA, [Ostracoda] CROLOSIBATL arm MARURA Plate XLV. Vol. WI. 33 Figs. 1 to ll. 1 to 3 4, 5. 6 to 8. 9 to ll. Figs. 12 to 14. Figs. 15 and 16. Figs. 17 and 18. Figs. 19 to 22. 19 and 20. 21. 22. Figs. 23 to 25. Figs. 26 to 29. 26 and 27. 28. 29. Figs. 30 to 34. Figs. 35 to 38. 35. 36 and 38, 37, Figs. 39 and 40. Fig. 41. Fig. 42. Figs. 43 to 46. 43 to 45. 46. PLATE XLVI. All the figures on this plate are magnified about twenty diameters. TETRADELLA QUADRILIRATA Hall and Whitfleld, sp.......-.-. eee cere eee eee 679 Posterior, side, and dorsal views of a right valve. Middle third of the Trenton shales, Minneapolis, Minn. : Another right valve. Birdseye limestone, High Bridge, Kentucky. Inner side of a right valve. Minneapolis. Three views of a left valve, differing from the usual form in unimportant partic- ulars. Minneapolis. Three views of a variety, agreeing with var. simplex in wanting the posterior marginal loculi. Trenton shales, Fountain, Minnesota. TETRADELEA, LUNATIPERA Ulrichisises:ss:se:eiaiee wo sieigie’s ai0's ¥ireisineipveietviaeie'a'e Pec ararasoiiaig 680 Three views of a left valve of a variety ot this species. In other specimens that were found with this one the antero-median ridge is more distinctly double. (See cut, p. 680.) Galena shales, Cannon Falls, Minnesota. MOOR BA: AN GIPTARIS, 11 SP iveccciesecscgeesea hice sieievetovendeacestsessrave: pareve wanrordanavaanaas ask aia va reeoresuheeeardiis 682 . (See also plate xu1II, fig. 89) Two views of a weather-worn valve, apparently of this species. Trenton shales, Fountain, Minnesota. ; MOOREA ((?): PERPLEXA; Dis SDs aie epi 6:e:5510 decease iecta tiene na WER Weeiebleacineesne: eek Sec ae 683 Side and sectional views of the remarkable valve upon which this species is founded. Trenton shales, Fountain, Minnesota. CERATOPSIS CHAMBERS Mill@? SPecccc cece ence cece cee se eereeseusninas vane te ease’ 676 Side and ventral views of a left valve of the usual form. Upper third of the Trenton shales, St. Paul, Minnesota. Inner side of a more elongate right valve, from the same locality. Another right valve from the same locality, peculiar in having the small post- median ridge divided. BOLLIA UNGULOIDBA, D. SP........... ARMEVROME IIS ASSEN eae axe RREMREE Rae S 669 Three views of a left (?) valve. Galena shales, Cannon Falls, Minnesota. BOLUEA SUB QUATA, M.S Piss i sdecie ciara aaverein die tyduaeud dsestsns dda dda ncaa aie asl Wolgara aren eto 669 End and side views of a valve of this species. Trenton shales, Fountain, Minn. A small valve from the same locality. Large and relatively high valve from the same position at Cannon Falls, Minn. DILOBELLA TY PA, ‘Ns Gens Cb Spies sis sarsiais sie vaciass ae eawe ee ise 80 ewes ae anes 673 Figures of three.valves showing slight variations. Upper third of the Trenton shales, St. Paul, Minnesota. DREPANELEA, BIGATHRATAS, De 'SPigace ssreveaunacmyegueienciaiaee and nora dideentnedmates 671 A right (?) valve of the usual size and appearance. Ventral and posterior views of a left valve. Interior of a right valve. Upper third of the Trenton shales, St. Paul, Minnesota. DICRANELLA BICORNIS, D. Gen. Cb. SP... eee eee ee eee cece eee ee eee eee eens 665 (See also plate xLiv, fig. 26.) Side and posterior views of a nearly complete right valve. Middle third of the Trenton shales, Minneapolis, Minn. DICRANELLA SPINOSA, D. SP. ..cce cee e reese eee eeee neces oe whoa Mele SAW RAEI RA TE Ree 665 (See also plate xLIv, fig. 23.) Posterior view of a left valve. DIGRANELGA. (7) ‘SUMBLBX, DS Pic. cceaceine snare incase seereuscatiacd 6.0 dy apes gin ieico ce otas een elosst evel cage iver ate 666 Ventral view of the valve figured on plate XLIV, figs. 24 and 25. FARUIECLA DABIOSAy Di SPieiacccndecws Games iieceyemsmkawergreals dae etermnrates 656 Anterior, dorsal, and left side views of an entire carapace. Galena shales near Cannon Falls, Minnesota. Somewhat weathered and relatively longer left valve: from the same locality. GEOVOGICAIA NANO RAL SHIS LOKXES UO RVUES@OFeMUN NESODAS Vol. II. (oO stracod a Plate XLVI.