VOL. L NO. 4, OCT, 1989 JOHN M. CLARKE ASSISTANT BTATE PALEONTOLOGI8T,. ALBANY Bee BL Bleek a ee ae Sg OF THE STATE OF NEW YORK eB een pepe ee ERIS EM, er Bae: QE 796 BA go oe | CORNELL UNIVERSITY Wy, |: | LIBRARY Es ENGINEERING LiBRARY The development of some Silurian Brachio 7 , / University of the State of New York MEMOLRS OF THE NEW YORK STATE MUSEUM VOL. I. NO. 1. OCT., 1889 - THE DEVELOPMENT OF SOME SILURIAN BRACHIOPUDA WITH EIGHT PLATES CHARLES E, BEECHER JOHN M. CLARKE T ASSISTANT STATE PALEONTOLOGIST CONSULTING PALBONTOLOGIST OF THE STATE MUSEUM ALBANY UNIVERSITY OF THE STATE OF NEW YORK 1889 QE Taha B4l++ a ( ABH! “CORNELL [UNIVER SiTy| LIBRARY 7 ——— TABLE OF CONTENTS TITLE PAGE, : TABLE OF CONTENTS, INTRODUCTION, . DISCUSSIONS OF THE SPECIES, CRANIA SILURIANA, Hall, ORTHIS ELEGANTULA, Dalman, ORTHIS HYBRIDA, Sowerby, STROPHOMENA RHOMBOIDALIS, Wilckens, STREPTORHYNCHUS SUBPLANUM, Conrad, STROPHONELLA STRIATA, Hall, STREPTIS WALDRONENSIS, Miller and Dyer, EICHWALDIA RETICULATA, Hall, ANASTROPHIA INTERNASCENS, Hall, RHYNCHONELLA ACINUS, Hall, RHYNCHONELLA NEGLECTA, Hall, RHYNCHONELLA WHITH, Hall, RHYNCHONELLA INDIANENSJS, Hall, RHYNCHOTRETA cunraTa, (Dalman) var. AMERICANA, Hall, ATRYPA RETICULARIS, Linnzus, RETZIA EVAX, Hall, RETZIA SOBRINA, Sp. N., CCLOSPIRA DISPARILIS, Hall, MERISTELLA meeereoarmas Ell MERISTINA nitrpa, Hall, WHITFIELDIA MARIA, Hall, - . e SPIRIFER CRISPuS, Hisinger, SPIRIFER CRISPUS, vat. SIMPLEX, Hall, SPIRIFER BICOSTATUS, (Vanuxem) var. PETILUS, Hall, SPIRIFER RADIATUS, Sowerby, SUMMARY OF DEVELOPMENTAL CHANGES, PLATES AND EXPLANATIONS, I-VIII Pace 5-12 13-95 13 13-17 17-18 18-22 23-25 25-29 30-31 31-32 32-34 35-36 37-39 39-42 42-47 47-5! 51-55 55-61 61-64 64-67 67-69 70-72 73-75 75-77 75-77 75-77 94-81 83-95 97 THE DEVELOPMENT OF SOME SILURIAN BRACHIOPODA By Joun M. Ciarxe and Cuaries E, BrEcHEr*™ INTRODUCTION The fossil faunas of our rock systems rarely furnish material for trac- ing the individual development of any of the contained species. Much will doubtless be done toward ascertaining such development when large collections from suitable localities have been studied with this object in view, and when the number of new species discovered and described each year approaches a minimum. We have a comparatively full and satisfac- tory account of the development of the individual organism in several species of trilobites, as given in the works of BARRaANDE, Watcort, Forp and Matruew; Hyarr, Branco, Moysisovics and others have demon- strated the developmental characters of many of the fossil cephalopods, and Verworn has elicited similar facts from certain extinct species of ostracoda. Farther than this but little has been attempted, although the field is a most extensive, important, and inviting one. As a general rule, the treatment of fossil organisms has rested mainly *The order of the names of the authors of this paper is without significance. The work was equally divided and jointly reviewed. 6 INTRODUCTION with geologists having more or less of a zoélogical training, and the prin- cipal aim has been to present the faunal aspects of each horizon for the purpose of chronological identification. This process has frequently become so involved’ with the imperfect description of species, that the systematic zodlogist or paleontologist is unable to make any use of a large proportion of the species as a means of studying their taxonomic relations or their structural affinities with each other and with recent forms. Each revision of a group of fossil animals has resulted in the establish- ment of numerous specific and generic synonyms. Many of these are owing, of necessity, to the imperfection of the material, and many names which are finally relegated as synonyms, have been created under a mis- conception of the full significance of age, sex, habitat and condition of preservation. Additional confusion often results from the inclusion, in a generic or specific description, of characters which pertain not alone to a normal individual, but interspersed with certain normal adult features are those belonging to various stages of morphological development and pe- culiarities arising from accident, disease and impoverished conditions. In the case of rare species, or of meager material belonging to common forms, it is to be noticed that assertions regarding specific and generic characters are usually very positive; while, with an abundance of speci- mens representing many stages of growth and the extremes of individual variation, the descriptions are qualified, the latitude of genera and species is extended, and the points of relationship with allied forms are multiplied, thus binding a group of organisms into comparative uniformity, without anomalous differences such as often occur where the dividing lines are rigidly drawn. During the years 1878-79, the collection of fossils made from the Niagara group at Waldron, Indiana, for the New York State Museum, was studied and arranged by one of the writers. This is probably the largest collection yet brought together from that celebrated locality, and INTRODUCTION 7 some conception of its size may be obtained from the fact that, when re- ceived, it weighed about seven tons. At the time mentioned, all the mature specimens were selected and specifically separated. Many imma- ture forms were also reserved and used in arranging the series pre- pared for exhibition in the State Museum. It was designed to represent in the arrangement, each species by a series of specimens showing the gradations of size and form from mature individuals down to as young and small specimens as could be found. Abnormal examples, also, were reserved and grouped with them. It. was the intention of the writers to accompany this memoir with photographic illustrations of these series, representing each species here discussed, but it has not been found wholly feasible, and the illustrations are largely restricted to the presentation of the immature and adult conditions of growth, with the exception of the several series which are given on plate 8. The product obtained from washing the slabs, was preserved and passed through sieves to assort the material into different grades of fine- ness. It was found that these washings contained a great number of partially developed shells, and it is from them that the extremely young brachiopods, treated of in the present paper, have been derived. The writers have carefully examined all the residue of these washings and have picked out about fifty thousand specimens, most of which are less than five millimeters in length, and many have a length of not more than one milli- meter. After all the imperfect and badly preserved individuals were rejected, there still remained more than fifteen thousand inchoate indi- viduals. The sediments at Waldron consist of fine calcareous shales, weathering into clays. A stratum of Niagara limestone overlies the shales at this locality, but none of the fossils derived from this limestone have been used in the preparation of the present paper, and so far as known, it has a com- paratively different fauna and does not furnish such material as is here 8 INTRODUCTION described. The calcareous matter in the shales consists almost entirely of fossils and fragments of fossils, principally branches of corals and bryozoa, segments of crinoid columns, and broken crinoid plates. The brachiopoda are all calcareous and the original shell structure is more or less preserved, depending upon the absence or presence of pyrite. The occurrence in such great numbers of immature shells in these deposits may be explained by the luxuriant fauna which flourished in this Niagara basin, by the quiet seas of this region and by the rapid sedimenta- tion of the shales. The richness of the material is shown by the great profusion of specimens representing the sponges, corals, crinoids, bryozoa, brachiopods, gastropods, annelids and crustaceans, comprising altogether about one hundred and fifty species. The lamellibranchs and cephalopods were also doubtless abundant, but the conditions existing for the preserva- tion of their remains were not favorable, probably on account of the com- position of their shells, and but sixteen species have been noted. That the fauna was protected from excessive storms and the action of sea currents, is evinced by the usual perfection of the fossils. Some of the crinoids are unbroken and remain attached by their roots, retaining their arms in place ; also, large colonies of delicate branching corals and bryozoa still preserve their unity. The specimens were rapidly buried in the soft calcareous mud and show none of the eroding or disintegrating action of the water, such as would have been produced had they lain for any considerable period unprotected on the sea bottom. It is true that many specimens are incrusted with bryozoa, annelids, cranias and other fixed and incrusting forms, but the majority of these seem to have flourished during the life of their hosts. Besides the embryonic brachiopoda occurring in these shales, there are other classes represented by immature forms, notably the gastropoda and crinoidea. These, with the brachiopoda, embrace almost all the young forms found. The small gastropods are of little interest, on account of the INTRODUCTION 9 limited number of species, and because they undergo no important modi- fication in their subsequent growth, and merely represent the apical portion of mature individuals. Among the crinoids, the modifications of form and structure from the embryo state to maturity are more profound and essen- tial, although the material is not sufficiently complete to furnish any very important results. It is necessary to state that nearly all our observations on the develop- ment of the brachiopoda are based upon the study of the material derived from a single locality, and sofme of the minor deductions may not apply, in every case, to the individuals of the same species found in other regions. The writers have also refrained, except when essential to the proper expo- sition of a species, from entering into details of synonymy or generic contro- versy as to the correct reference of the species. This course is considered advisable, from a desire not to introduce any discussions alien to the descriptions of the developmental changes in these organisms. Aside from this, it is believed that a number of important facts are here added to the knowledge of the brachiopoda, and that many of them will be found to be of general application. The investigation has also resulted in elucidating several obscure and anomalous features of the shell and of the cardinal area, which appear in their proper place in the description of the spe- cies and in the general summary. The following list includes all the species of brachiopoda which, up to this time, have been described from the shales at Waldron, Indiana, and comprises forty-two species and varieties, ascribed to twenty-four genera. It also shows whether material has been obtained which furnishes data for tracing the developmental changes. The majority of the species which have afforded no young specimens are rare forms even in their adult state. Among the actually abundant species of which there are no means accessible of tracing the life-history, Rhynchonella stricklandi is a noticeable example, and it is really the only 2 10 INTRODUCTION common species which has afforded no young shells. Whztfeldia maria, another abundant form, furnishes a series which is notably incomplete, as the youngest individual observed, which can with certainty be referred to it, has a length of 6 mm. Likewise, the inarticulate species have yielded almost no immature specimens. List OF THE BRACHIOPODA OCCURRING IN THE NIAGARA SHALES AT WaLpRON, INDIANA Cranta stlurzana, Hall, Crania setifera, Hall, Crania spinigera, Hall, Lingula gtbbosa, Hall, Pholidops ovalzs, Hall, Orthis hybrida, Sowerby, Orthis elegantula, Dalman, Orthis subnodosa, Hall, . Orthzs béloba, Linnzeus, Streptorhynchus tenue, Hall, Streptorhynchus subplanum, Conrad, Strophomena rhombotdalzs, Wilckens, Strophodonta profunda, Hall, Strophonella striata, Hall, Strophonella semifasczata, Hall, Leptena transversalis, Dalman, Streptis waldronenszs, Miller and Dyer, Chonetes nova-scotica, Hall, Chonetes undulata, Hall, Etchwaldta reticulata, Hall, Pentamerus fornicatus, var., Hall, Anastrophia tnternascens, Hall, Rhynchonella neglecta, Hall, Rhynchonella acinus, Hall, Rhynchonella endéianensis, Hall, Rhynchonella white7, Hall, Rhynchonella strickland?, Sowerby, Rhynchotreta cuneata, Dalman, ° One embryo. No young shells obtained. “eo oe Numerous inchoate specimens. ce ce No young shells obtained. ae ae éo oc Full series, showing development. ve ae No young shells obtained. Full series, showing development. No young shells obtained. 66 vc One embryo. No young shells obtained. cc oc Young shells not rare. No young shells obtained. Young shells not rare. Young shells very abundant. ce 6c Mature form abundant; no young shells obtained Young shells common. INTRODUCTION U1 Atrypa reticularzs, Linneus, . . Young shells abundant. LZygospira minima, Hall, ‘ No young shells obtained. Celospira déspardirs, Hall, . § . Young shells common. Retzia evax, Hall, : : i Young shells very abundant. Retzia sobrina, sp. n. ; ‘ 4 Young shells not rare. *Nucleospira pistformzs, Hall, 5: ee m Meristella rectirostra, Hall, ‘ Full series, showing development. Merzstina nit¢da, Hall, . Numerous inchoate specimens. Whitfeldta marta, Hall, . ; . Incomplete series showing development. Spirifer eudora, Hall, . ‘ No young shells obtained. Spirifer crispus, Hisinger, 3 Full series, showing development. Spirifer crispus, var. simplex, Hall, Hf Spirifer radiatus, Sowerby, : - Spirifer bicostatus, var. petzlus, Hall, e a The method of illustration which has been adopted is one which seems most readily to furnish a means for comparison of characters. The embryonic shells are represented as enlarged, usually to the size of an adult, and accompanying the enlargements are natural size representations of the final result of normal growth. Where the mature forms have been too minute to show satisfactorily the details of structure, both the develop- mental stages and full grown shell have been enlarged to a convenient size. Thus the incipient stages and mature specific form are presented together. In the delineation of special features, such as the hinge, we have sometimes enlarged the earlier phases to a size corresponding with the same structure in the mature form, or have increased all on a uniform scale, so that both the particular characters and their comparative size are presented. The enlarged drawings have been made by the writers, principally from the microscope; the camera lucida was employed to ensure accuracy in outline. The illustrations of the mature specimens are largely taken from the Twenty-eighth Annual Report of the New York State Museum *The mature characters of this species are assumed so early, that the youngest forms ob- served show no important differences from the adult. On this account, no discussion of its characters is given in the ensuing pages. 12 INTRODUCTION and from the Eleventh Report of the State Geologist of Indiana, which may be consulted for a more ample representation of the adult characters of the species occurring at Waldron. The drawings on plates 1 to 7 have been reproduced on stone, in a most satisfactory manner, by Mr. Purtip Ast, and we wish to express our appreciation of the skill and labor he has bestowed upon the work. The illustrations given on plate 8 were made from photographic reproductions of the actual series of specimens, and, although not serviceable for purposes of detailed study, show distinctly the nature of the material used and the almost insensible gradations obtained, representing the life-history of these species. Thesame completeness of material is furnished by the majority of forms described in the following pages. The arrangement of the subject-matter in the discussions of the species may not seem to be in accordance with the usual method employed in trac- ing the life-history of organisms. In this case we are dealing with fossil organisms and, in order to insure accuracy of results, it is necessary to begin with the known and established facts and gradually descend to to minute and strange forms, thereby connecting the extremes of growth, Under the caption, ‘“‘ Developmental Changes,” we have, however, endeav- ored to trace the history of each feature of the shell, from its inception to maturity. DISCUSSIONS OF THE SPECIES CRANIA SILURIANA, Hall, 1863 PuaTE I, Fics. 1, 2 —— —, Hall. Twenty-eighth Ann. Rept. N. Y. State Mus. Nat. Hist., p. 148, pl. 21, figs. 3-7. 1879. — -—, Hall. Eleventh Ann. Rept. State Geol. Indiana, p. 282, pl. 21, figs. 3-7. 1882. But a single embryo of this species has been found in all the material examined. It is of an incipient stage of growth, measuring but 1 mm. in height, and 1.5 mm. across the aperture. Compared with the mature form, the average size of which is about 9x20 mm., it shows a relatively greater elevation and a more regularly conical form. Otherwise, all the few essential characters of the adult shell are present at this early age. ORTHIS ELEGANTULA, D&lman, 1827 PLATE I, Fics. 3-11 —— ——, Hall. Twenty-eighth Rept. N. Y. State Mus. Nat. Hist., p. 150, pl. 21, figs. 11-17. 1879. —— ——, Hall. Eleventh Ann. Rept. State Geol. Indiana, p. 285, pl. 21, figs. 11-17. 1882. Both the species of Orthzs occurring at Waldron (O. elegantula and O. hybrida) are very abundant. In the later stages of growth, the former species is readily distinguished from the latter by its flatter and shallower dorsal valve and deeper ventral valve, features which usually hold good for purposes of discrimination ; but in extremely early stages of growth, the nearly equivalve form of the shell makes the separation of the species very 14 MEMOIRS OF THE STATE MUSEUM difficult, perhaps even impossible. Between the dimensions of .5x.75 mm. and 18.5x18 mm. (which is a little in excess of average mature size), we have found every gradation in size and development. The minute shell which serves as a starting point for the series may quite as well be taken as the incipient shell of Orthis hybrida, as both its valves have the same depth, while the cardinal areas and beaks show the same character of development. As there can be no doubt of this fact, it becomes impossible to determine whether a given embryo, could it have grown to maturity, would have developed into O. hybrida or O. elegantula. Until the embryos reach a size of 2 or 2.5 mm. in length, their specific value is undeterminable, and the specific individuality of O. elegantula can be established only with the increasing depth of the ventral valve from this point upward toward adolescence. Unless our observations are at fault, and they have been made with great care, evidence here is very positive, that the diagnostic characters of species of this genus may not be assumed until the earlier stages of the existence of the shell have passed... Indications of similar character are found among the species of ARAynchonella and Spirzfer. The importance of the fact is apparent and its significance will be appreciated. SPECIFIC CHARACTERS Mature Form (plate 1, figs. 10-12@). Outline subcircular ; hinge line short, about one-half the width of the shell, straight. Ventral valve elevated along the dorsum, which is arched and slopes more rapidly toward the lateral than toward the anterior margin ; greatest width below the hinge-line, about half-way down the valve. Beak full, arched, incurved, and projecting over the cardinal area sufficiently to conceal the foramen. Cardinal area broadly triangular, low, incurved; foramen triangular ; deltidial plates absent. Dorsal valve shallow, nearly flat, slightly rounded over the umbo, but depressed toward the margins. A sharply defined sinus starts near the SILURIAN BRACHIOPODA 15 apex, but by widening with the growth of the shell, it becomes nearly obso- lete before reaching the margins. Cardinal line straight ; cardinal area narrow, elongate triangular ; beak inconspicuous. Foramen triangular and filled by a tripartite cardinal process which passes into, without filling the foramen of the opposite valve. Surface of the shell closely covered by fine thread-like strize which increase by intercalation ; concentric growth-lines rare, except near the margin where they appear as wrinkles. Incipient Form (plate 1, figs. 3, 3a). The initial shell of our series, measuring .5 mm. in length and .75 mm. in width, has valves of equal depth and convexity. The-length of the hinge-line nearly equals the great- est width of the shell. The cardinal area is high, and equally elevated on each valve. Beaks erect; foramina large, triangular, open and marginate. On the ventral valve is a single median stria, representing the dorsum of the mature shell, accompanied by one and indications of a second on each of the lateral areas, making three (i.e., five) striae on the valve. On the dorsal valve a low and wide median depression is apparent, bounded by two central striae, these being accompanied by two accessory pairs upon the latera, making six striz in all. It is very probable that this form represents the actual initial stage in the development of the shell, and if this is the case, the inception of the plications on the surface, which become so numer- ous at maturity from (from one hundred to one hundred and thirty on each valve), is synchronous with the formation of the rudimentary shell, while in the pauciplicate species here discussed they appear to be of secondary growth. DEVELOPMENTAL CHANGES General Form and Outline. In the growth of the shell a change be- comes manifest in its outline and relative proportions. The young stages have the width greater than the length, but the more rapid axial growth of the shell reverses these proportions in maturity. Moreover in the incipient stages, the valves, as already noticed, are of nearly equal depth and con- 16 MEMOIRS OF THE STATE MUSEUM vexity. In the next stage, the depth of the ventral valve has noticeably increased over that of the dorsal, and, as in the latter valve the median sinus has become distinctly developed, the difference in this respect becomes emphasized. The divergence of the valves in convexity becomes increased until maturity, and this growth is accompanied in the ventral valve by a correspondingly increasing incurvature of the beak. Beaks. In the incipient shell, the beaks are erect and distant, but not prominent. By the development of the broad sinus on the dorsal valve, the beak of this valve becomes relatively less prominent and apparently more closely appressed to the cardinal line. On the opposite valve, every increase in convexity is accompanied by a corresponding: increase in the incurvature of the beak, and as the shell approaches maturity, the incurvature becomes so great, that it has been necessary, in the drawings which are here given showing the features of the cardinal area, to represent the beak as broken away. Foramen. The earliest stages of growth show a remarkable feature in the triangular, marginate, subequal fissures on the valves. This character may prove of a high taxonomic value, as it clearly indicates the relation- ship, in this respect, of Or¢hzs to the Linguloids, and places the genus near the inarticulata. The foramen upon the ventral valve is, in every stage of development, open and free for the protrusion of the pedicle. Del- tidial plates are absent in every stage of growth. Ina secondary stage, a cardinal process begins to form in the apex of the dorsal foramen, soon widening and becoming tripartite. As age increases, this process is projected into the ventral foramen, never quite filling it, always leaving room for the protrusion of the pedicle. In immature conditions the cardinal process is attached to the shell only at the apex of the foramen, but with ma- turity it comes in contact with the sides of the foramen, and at this stage entirely fills the dorsal aperture. With the increasing incurvature of the ventral beak and cardinal area, the apertures of the two valves SILURIAN BRACHIOPODA 17 change their mutual angle, constantly lessening it as growth ad- vances. Plications. As noticed above, the earliest stages of growth observed show the striz to be already developed on the shell, five on the ventral and six on the dorsal valve. These plications are rapidly multiplied by interstitial addition, and in maturity number from one hundred to one hundred and thirty on each valve. ORTHIS HYBRIDA, Sowerby, 1839 PLATE I, Fics, 13-18 —— —-, Hall. Twenty-eighth Ann. Rept. N. Y. State Mus. Nat. Hist., p. 149, pl. 21, figs. 18-25. 1879. —— —, Hall. Eleventh Ann. Rept. State Geol. Indiana, p. 285, pl. 21, figs. 18-25. 1882. Orthis hybrida passes through primary developmental stages which are essentially identical with those already described for O. elegantula. Sufficient has been said in that connection in regard to the similarity and ' probable identity of the earlier embryonic stages of the shell of both spe- cies, the origin of the entire specific difference which is so apparent in the later and mature periods of development lying in the unequal growth of the valves in convexity. This increase is relatively greater in the dorsal valve of O. hybrzda than in that of O. elegantula, and less in the ventral valve of the former than in that of the latter species. Thus O. hydrida is a more discoid, lenticular shell, showing but slight evidence of a median fold and sinus and carrying on its surface at maturity just about as many plications or striz as its associate. There is an obese variation from the normal form of O. hydrida, which was noticed by Professor Hau (loc. cz¢.), and this appears early in the development of the species, with a size of 3.5 mm. in length and 4.5 mm. in width, and reaches a maximum growth with dimensions of 14x13 mm. This variation is due to internal thickening and increase in convexity, and is accompanied by abundant concentric growth-lines which are as 3 18 MEMOIRS OF THE STATE MUSEUM rare in the normal form as in O. elegantula. Our representative series of this species affords variations between the following limits of size: .5 mm. length x .75 mm. width (minimum), and 17 mm. length x 20 mm. width (maximum). STROPHOMENA RHOMBOIDALIS, Wilckens, 1769 Puate II, Fics. 1-13 —— —~, Hall. Twenty-eighth Ann. Rept. N. Y. State Mus. Nat. Hist., p. 151, pl. 22, figs. 4-10, 1879. —— —, Hall. Eleventh Ann. Rept. State Geol. Indiana, p. 288, ‘pl. 22, figs. 4-10. 1882. This well known species, although extremely abundant in the mature state, is correspondingly rare in its undeveloped condition. The young specimens which have been found are nearly all more or less broken, and it is evident that while young, the shell was thin and delicate, consequently few of their remains have been preserved. The series which has been selected is, however, very complete in its representation of the distinct phases of growth through which the individuals pass in their development from youth to maturity. The initial form, without radiating strie; the second phase, a shell radiatingly striate, without undulations; the third state, striated and concentrically undulated, but without the angular geniculation of the valves in front; and the last phase, with the full form and characters of maturity, offer a series of changes, not often trace- able in Silurian brachiopods. . The development of the characters of the hinge-area is also very sat- isfactorily demonstrated and affords some interesting points of comparison with certain forms of Streptorhynchus and Strophonella. These features are noticed at the end of the description of the species, S¢rophonella striata. SPECIFIC CHARACTERS Mature Form (plate 2, figs. 4, 4a, 10, 13). Shell semi-elliptical or semicircular in outline. SILURIAN BRACHIOPODA 19 Dorsal valve flat or slightly concave in the upper part, with the marginal portions abruptly curved upwards in front; beak small, carrying on its inner side, a large, prominent, triangular callosity, grooved along its summit and nearly filling the area of the opposite valve. Ventral valve usually convex in the upper part, becoming flat or concave below, and with the marginal portion produced and abruptly bent downwards, geniculating with the dorsal valve; beak small, usually per- forated with a small circular foramen; hinge-line often 50 mm. in length, equaling or greater than the width of the shell below ; cardinal extremities twisted and often much extended; cardinal area narrow, edges parallel, formed by both valves; deltidial area of the ventral valve, broadly triangu- lar, occupied by the grooved callosity under the dorsal beak. Surface marked by regular, rounded, radiating stria. From the beaks to the curtain, or geniculated portion, the shell is ornamented with regular, strong, concentric undulations or corrugations. This species varies greatly in size and form, in the different horizons and localities where it is found. In many places the mature shells are about half the size of the specimens from Waldron. Incipient Form (plate 2, figs. 1, 1a, 11). The smallest entire speci- men yet detected has a length of 1.25 mm. The outline is semi-oval, with the greatest width near the middle, and about one-fourth greater than the length. Dorsal valve convex in the upper part, becoming concave toward the front. The hinge-area of this valve is very narrow and linear, and carries beneath the beak a small grooved callosity. Ventral valve convex, sloping in all directions from near the foramen, around which the surface is slightly depressed. There is also a depression extending along the middle of the valve to the anterior margin. The place of the beak is occupied by an exsert, conical pedicle-tube, which partly protrudes beyond the cardinal margin of the valve and extends down to, and embraces the dorsal callosity. Cardinal area of the ventral valve comparatively broad, narrowing rapidly 20 MEMOIRS OF THE STATE MUSEUM from the pedicle-tube to the extremities. Surface smooth, except along a narrow Zone around the margin, which shows incipient radiating strie. DEVELOPMENTAL CHANGES The form of this species being somewhat complex, we may make a convenient subdivision of the development of the shell into four stages, which may be briefly characterized as follows: rst Stage. Length of shells’ .4-1 mm.; surface smooth. 2d Stage. Length 1-2 mm.; shell radiatingly striated, without undulations. 3d Stage. Length 2-20 mm.; shell radiatingly striated, and concentrically undulated. 4th Stage. Length 20-30 mm., entire shell radiatingly striated, concen- trically undulated in the upper part, abruptly produced and geniculated in front. The changes taking place in the form and character of the shell from one stage to another can best be shown and used for comparison in the following tabulation, where the conditions incident to each stage of growth in the various parts of the shell are briefly described. Development of Strophomena rhombordales | 1st Stage. 2d Stage. 3d Stage. 4th Stage. | Initial. i Infantile. Adolescent. Matitre. | | SiZeiccne aie sce 4 mm.—Imm.in I mm.—2 mm. in 2mm.— 20 mm. in 20mm.— 30mm. in length, 4 mm.— length, 1.5mm.— length, 2.5 mm.— __ length, 4o mm.— 1.5 mm. in oe 2.5mm. in width. 40 mm. in width. 50 mm. in width. | ! | ! FOrMseos deebaite | Transversely semi-. Transversely semi- Longitudinally Longitudinally | oval; cardinalex-, elliptical; cardi-- semi-elliptical; semi-elliptical; tremitiesobtusely nal extremities cardinal extremi-. cardinal extremi- | angular. | angular. ties angular, be- ties acutely angu- coming produced, lar, extended and not twisted. twisted. SILURIAN BRACHIOPODA 2I Development of Strophomena rhombotdal’s — Continued ist Stage. 2d Stage. 3d Stage. 4th Stage. Initial. Infantile. Adolescent. Mature. 7 Contour .. ....| Convex. Depressed convex.| Very slightly con-| Geniculate, making vex. the shell highly arched longitudi- nally. Dorsal valve....] Convex, concave] Concave,except on| Concave,except on| Flat or concave on Ventral valve... Surface Cardinal area... Pedicle-tube.... Foramen Dorsal callosity. on the margin; umbo prominent. the umbo. the umbo. the body of the shell; abruptly produced and curved upwards around the mar- gins. + Convex. Convex, semi-coni-| Convex in the up-} Convex in the up- cal with the beak; per part, flat or; per part, flat or at the apex. concave on the] concave in the margin. middle, and ab- ruptly bent down- wards below. Smooth, Radiatingly striate.| Radiatingly striate] Entire surface, and _ concentri- cally undulate. radiatingly _ stri- ate, concentrical- ly undulate in the upper part only. Ventral high; dor- sal very slender. Ventral high; dor- sal very slender. Ventral narrow; dorsal narrow. Both narrow, sub- equal. Exsert, full height of the area. Not exsert, full height of the area. Nearly full height of the area. Obsolescent or ob- solete. Present, circular, elevated. Present, circular. Present, circular. Usually present. Small, grooved. Small, grooved. Larger, grooved. Very large and deeply grooved. a2 MEMOIRS OF THE STATE MUSEUM Among the mature shells, the greatest variation is to be found in the development of the anterior curtazn, or geniculate and_ sloping marginal area of the valves. In some specimens this is so excessively developed, that the posterior, or concentrically undulated portion of the ventral valve is at right angles to the plane of the margin. Also, in many specimens the curtain is obscurely plicate, and the radiating striz are often irregular and sometimes fasciculate, while on the upper part of the valves these striae are very uniform in their arrangement. No speci- mens have been noticed which are so strongly quadriplicate as those illus- trated by Mr. Davipson, on plate 39 of the “ British Silurian Brachiopoda.” Senile specimens usually have the valves very much thickened from internal growth, and the margins show strong varices. It is noticeable that nearly all the old shells are covered with a growth of cranias, bryozoa, favosites, etc., and it is very difficult to free the shell from this overgrowth. In consequence of this, many of the shells are scarcely recognizable, and resemble agglomerations of bryozoa and corals. The only other species of brachiopoda at this locality commonly thus over- grown and involved, is Atryfa reticularcs. Strophomena rhombordalts is cosmopolitan and has been discussed by many authors who have shown its great variation and wide distribution. So far as known, the youngest specimen heretofore figured is one repre- sented by Mr. Davipson.* This is an individual belonging to the third stage of development, having a length of nearly 6 mm. and a distinct circular perforation of the beak. * British Fossil Brachiopoda, Vol. III, Devonian and Silurian, pp. 283, 284, pl. 30, fig. 6. The same. General Summary to the British Fossil Brachiopoda, p. 289. SILURIAN BRACHIOPODA 23 STREPTORHYNCHUS SUBPLANUM, Conrad, 1842 PLATE II, Fics, 14-20 -—~ ——. Hall. Twenty-eighth Ann. Rept. N. Y. State Mus. Nat. Hist., p. 151, pl. 21, figs. 26-33. —— a fit Eleventh Ann. Rept. State Geol. Indiana, p. 288, pl. 21, figs. 26-33. 1882. The series selected to represent the development of this species com- prises fourteen specimens ranging from 1.5 mm. to 26.5 mm. in length. The external features of form and surface ornaments are remarkably constant from the young to the mature shells. There is, however, a slight progres- sive modification in the relative convexity of the valves. The dorsal valve of young and half-grown individuals is nearly flat, while the ventral is moderately convex. In old specimens both valves are convex, with the dorsal somewhat more so than the ventral. The most marked changes due to advancing growth are those which take place in the hinge. Some men- tion of these is made under the description of Strophonella striata, where it is stated that the pedicle-tube retains its embryonic form and size nearly up to maturity, after which it is obscured by the internal thickening of the shell ; also, that the callosity under the beak of the dorsal valve uniformly increases in size from the youngest forms to full-grown specimens. SPECIFIC CHARACTERS Mature Form (plate 2, figs. 15, 15a, 17, 20). Shell semicircular or semi-elliptical, depressed convex; hinge-line longer than the width of the shell; cardinal angles flat and extended. Dorsal valve moderately and uniformly convex except at the cardinal angles ; umbo not defined ; beak small. Ventral valve convex on the umbo, less convex below, and in many specimens the marginal portion is flat or slightly concave; beak small, somewhat arched. Hinge-area nearly equal in both valves, usually appear- ing as a deep angular groove along the cardinal margin. Under the beak of the dorsal valve is a large triangular callosity, grooved on the inside, 24 MEMOIRS OF THE STATE MUSEUM and nearly filling the fissure of the opposite valve. Deltidium of the ven- tral valve broadly triangular, extending to just below the’ beak, and mar- gined on each side by two narrow areas in the form of scalene triangles, which may represent the deltidial plates of other genera. Beak imperforate. Surface marked by from fifty to one hundred (according to the size of the shell) regular, rounded striae, with equal interspaces, increasing in num- ber by interstitial additions. The entire shell is also ornamented with very fine, regular, sharp, concentric striae. A large specimen has a length of 26 mm., and the width, measured along the hinge-line, is about 38 mm. Incipient Form (plate 2, figs. 14, 142). The smallest specimen: measures 1.5 mm. in length, by 2.3 mm. in width along the hinge-line. The outline is semielliptical, with the cardinal angles slightly extended. Dorsal valve concave in the upper part, and slightly convex below. Ventral valve convex ; beak prominent, projecting beyond the hinge-line. The hinge characters are not well preserved in this individual. The first specimen in the ascending series which shows the hinge distinctly, has a length of 2.25 mm., and will be described in the development of this. part. The surface of the incipient shell is marked by seventeen alternating, narrow, elevated radiating lines, with wider interspaces, and also shows sev- eral lines of growth near the margin. DEVELOPMENTAL VARIATIONS No marked changes occur in the general form of the shell, other than the gradual increase in the convexity of the dorsal valve and in the exten- sion of the cardinal angles. The dorsal valve is usually quite flat in speci- mens having a length of 10 mm. or less. The radiating lines increase in -number by interstitial additions, from the youngest form to maturity, and the fine concentric striz appear on all the specimens, including the initial individual in the series, where they are developed around the margins of the valves. The earliest phase of the hinge yet noticed, is found in a specimen SILURIAN BRACHIOPODA 25 having a length of 2.25 mm. The dorsal valve shows a foramen in the cardinal area under the beak, margined by a slight thickening of the shell. The ventral valve preserves a small perforate pedicle-tube at the apex, extending about two-thirds of the distance down to the hinge, below which is a triangular deltidial opening of the same width as'the dorsal foramen. A specimen 4 mm. in length (plate 2, fig. 19), shows a more advanced development of the same parts. The dorsal callosity has nearly filled the sinus under the beak and has a narrow groove in the center. The fissure of the ventral valve has increased considerably in size and relative height, showing narrow marginal plates, or defined areas which may be deltidial plates. The pedicle-tube is still perforate, but has not increased in size beyond the initial stage. From this point to maturity, the hinge increases in width, the dorsal callosity grows rapidly and nearly fills the fissure of the opposite valve. The pedicle-tube is obscured and the perforation obsolete. The deltidial plates, or lateral areas, are clearly defined, and have the form of narrow scalene triangles. No important variations have been noticed among the mature speci- mens. Occasionally an individual diverges from the normal form by having mucronate cardinal angles, or a senile specimen shows strong imbricating varices of growth, but, as a whole, the form and surface ornaments in this species are very uniform. STROPHONELLA STRIATA, Hall, 1843 PLATE III, Fics. 1-8 Strophodonta striata, Hall. Twenty-eighth Ann. Rept. N. Y. State Mus. Nat. Hist., p. 152, pl. 23, figs. 1-6. 1879. —— —, Hall. Eleventh Ann. Rept. State Geol. Indiana, p. 290, pl. 23, figs. 1-6. 1882. The present form is one of the most delicate and fragile species of brachiopoda at Waldron. Individuals are not of rare occurrence, but the majority of them are more or less broken. The upper portion of the shell, a 26 MEMOIRS OF THE STATE MUSEUM or that along the hinge, being thicker and stronger than the remainder, is more often preserved, and the series is only complete in the representation of this portion, although there are several small specimens which are sufh- ciently entire to show the early form of the shell. As in the other species which, in their mature proportions, depart from the type of structure in the group, the incipient shell is found to revert to the primitive form. The full-grown examples of this species are concavo- convex, the concave valve being the ventral, while in the young, the ventral valve.is the more convex. This change in the relative convexity of the valves does not begin until the individuals are about half-grown, and is pro- duced by the gradual deflection of the margin with the increase in the size of the shell. The development of the features of the hinge is very characteristic, 7 and, as in the other strophomenoid forms, is of primary interest. Both the dorsal callosity and pedicle-tube continue to increase in size with the growth of the shell, from the incipient form to maturity. SPECIFIC CHARACTERS Mature Form (plate 3, figs. 2, 2a, 8). Shell semi-elliptical, wider than long, the greatest length being along the hinge. The body cavity is very shallow, and the shell has a concavo-convex form. Dorsal valve flat in the upper part, moderately convex in front. [’en- tral valve slightly convex on the umbo, and concave over the remainder of the valve. Hinge-area formed by both valves. Ventral area the wider, carrying in the center a small conical pedicle-sheath which is usually min- utely perforate at the apex. Dorsal area linear, with a callosity in the middle, under the pedicle-tube of the opposite valve. Test thin, surface ornamented by about fifty alternating radii, with three or four fine filiform striz in each interspace; also crossed by fine irregular strie of growth. SILURIAN BRACHIOPODA 27 Two specimens measure respectively, 19.5 mm. and 14 mm. in length, and 23 mm. and 16 mm. in width, at the hinge. Incipient Shell (plate 3, figs. 1, 1a, 3). The form is nearly plano- convex. Dorsal valve convex on the umbo, flat below. Ventral valve moder- ately convex, with a prominent pointed beak. Hinge narrow, with a small cylindrical perforated pedicle-tube in the center of the ventral area, anda small callosity in the dorsal area. In the smallest specimen observed, the surface is marked by eleven radii on the ventral valve, but is otherwise apparently smooth. Length 2.25 mm.; width in the center, 3 mm. DEVELOPMENTAL CHANGES On account of the imperfection of the material, it is impossible to trace any minor changes in the outline of the valves, and the specimens indicate that no considerable transformation took place. The modifications in the convexity of the valves is of more importance in this species, and can be readily observed. In the young individuals, up to about one-third full size, the ventral valve is slightly convex and the dorsal valve nearly flat. Further growth of the shell changes these relations, by the gradual deflec- tion of the margin, until the general form of the ventral valve is concave and the dorsal valve is convex. The radii appear very early in the growth of the shell, the smallest individual having eleven on the ventral valve, the majority of which extend to the umbo. They probably first appeared in pairs and are found’ to increase in number afterward by simple intercalation. The hinge-area is developed upon both valves in all stages of growth, although in the early stages the cardinal area of the dorsal valve is very narrow, but gradually increases, until at maturity, it is nearly equal to the area of the ventral valve. The pedicle-tube is at first cylindrical and short. Advancing in the series, it is found to become conical from growth, and from the widening of the fissure, until, in full grown specimens, it is wider than high. A careful 28 MEMOIRS OF THE STATE MUSEUM examination reveals the perforation in all stages of the development of the shell. It is, however, very minute, and it is not probable that the extremely small peduncle could have performed its full function. Indeed, it may be surmised that in none of the three strophomenoid species here described was the fleshy arm sufficiently strong in mature individuals to serve as a secure support to the shell. In the embryonic forms it was a more impor- tant organ. The hinge of the young shell illustrated in figure 4, plate 3, shows an excessively elongate, cylindrical pedicle-tube, of which more than one- half the length is projected above the beak. It must be considered as a supra-calcification about the peduncle, and apparently indicates a more complete functional extension. The grooved dorsal callosity appears in the beginning of the series, and gradually increases in size, and detrudes so that the groove shows on the exterior, but just before maturity it is either filled, or introverted into the deltidial cavity. THE FEATURES of the hinge, fissure and callosity, in the Strophomenide, and their embryological development, seem to be peculiar to the group. They are of special interest both on this account, and also because the family has no living congeners. Although the separate characters have been presented in detail in each of the preceding descriptions, a brief review of the hinge characters is here given, showing more clearly their intimate relationships. In the three species, Strophomena rhomboidalis, Strophonella striata and Streptorhynchus subplanum, the initial form of the hinge is the same. Each shows a slender callosity under the beak of the dorsal valve, and a perfo- rate pedicle-sheath in the ventral valve, which does not entirely close the deltidial opening. From this initial stage, development proceeds in a dif- ferent manner for each of the three species. Strophomena rhombotdalis and Strophonella strrata develop in a parallel series until the individuals are SILURIAN BRACHIOPODA 29 about one-third grown in the first species, and two-thirds full size in the second. That is, the dorsal callosity and pedicle-sheath each increase uniformly in size up to these periods. Beyond this the divergence is rapid and marked. In Strophomena rhombotdalis, the grooved callosity increases in size, so as to nearly fill the broad fissure in the ventral valve, while the pedicle-sheath ceases growth, is atrophied and lost, although, in many cases, the perforation persists. Strophonella striata continues its hinge de- velopment without a change, except that, at full maturity, the groove on the callosity becomes introverted into the pedicle-sheath. The third mode of development is exhibited by Strchtorhynchus subplanum, in which the pedicle-sheath does not increase beyond its initial size, while the dorsal callosity develops up to the maturity of the shell, and, as in Strophonella striata, the groove is on the inner side. The function of this groove in the callosity of the dorsal valve in the strophomenoids has not been satisfactorily determined, its existence having sometimes been considered as evidence of the perforation of this valve.* In all young shells, it is evident that the passage of the pedicle is not through this groove in the dorsal callosity, but through the apex of the ventral valve by means of the channel which has been here termed the pedicle-tube or sheath. In growth-stages where there can be no ques- tion of the functional activity of this sheath, the dorsal callosity is already grooved or sinuate. It might be surmised that the purpose of the groove was to avoid compressing the pedicle when the valves were open, and this it may have been to some extent; but the evidence furnished by both recent and fossil species indicates that the valves of the articulate brachio- pods could be opened only a very slight degree. The groove persists in species after the true pedicle-perforation in the ventral valve is closed and functionally useless. Its origin appears to be due to the organic deposition about the bases of the two interior cardinal processes, the interstitial area of slower deposition being represented by a fissure, groove or sinus. *Eleventh Rept. State Geologist Indiana, pp. 288, 289. 1882. 30 MEMOIRS OF THE STATE MUSEUM 6 STREPTIS WALDRONENSIS, Miller and Dyer, 1878 PLATE III, Fics. g, 10 Spirifera? waldronensis, Miller and Dyer. Contributions to Paleontology, Jour. Cinti. Soc. Nat. Hist., April, 1878. Triplesia putillus, Hall. Trans. Alb. Inst., vol. x, Abstract, p. 16. 1879. ——, Hall. Eleventh Ann. Rept. State Geol. Indiana, p. 298, pl. 27, figs. 19-22. 1882, This species is among the rarest of the Waldron brachiopoda and it is impossible to present a series representing the variety and progress of development, as in some of the more common forms. There were but two specimens, both adults, discovered in the State Collection at the time of thé publication of the “ Descriptions of New Species of Fossils from the Niagara Formation at Waldron, Indiana.” * Fortunately, we have more recently detected a young individual of about one-fourth the normal adult size, which offers some interesting details in its form and characters. The asymmetry of the shell is manifest even at this early stage of growth (although the median fold is not developed), and is evinced by the position of the beak of the ventral valve, and by the contour of the margins. It is probable that in a still earlier phase of growth, the two valves are symmetrical, or nearly so. In the young individual under consideration (plate 3, figs. 9, 9a, 94), the outline is nearly circular. The beak of the ventral valve is very much elevated, projects beyond the cardinal line and is directed toward the left side of the shell. The apex is truncated, and the opening is confluent with the area below. The cardinal area is high, forming a large triangular fissure which is apparently not closed by deltidial plates. The beak of the dorsal valve is depressed, and limited by a slight furrow on each side. No lines of growth are visible, but the surface is somewhat granulose, as in many small shells of other species. *James Hall. Read before the Albany Institute; March 18, 1879. SILURIAN BRACHIOPODA ar The principal differences to be noted in comparison with the adult individuals are the subcircular outline of the shell, the depressed valves, the absence of a median fold, and the large deltidial area. EICHWALDIA RETICULATA, Hall, 1868 PuaTeE III, Fics. 11-13 ——~ —~—, Hall. Twenty-eighth Ann. Rept. N. Y. State Mus. Nat. Hist., p. 169, pl. 26, figs. 50-54. — = Bl Eleventh Ann. Rept. State Geol. Indiana, p. 312, pl. 26, figs. 50-54. 1882. Very few of the earlier growth stages of this species have been observed and these show but comparatively little variation from the features of the normal adult. On plate 3 is given a figure of the youngest example found, which has a length and width of 3 mm., while the usual adult is about 16x16 mm., varying in relative proportions with the increase of senile obesity. The change in outline during growth is from subcircular to subtriangular, and in earlier stages, the ventral fold and sinus are very ill-defined. The peculiar triangular exfoliation of the shell on the umbo of the ventral valve is evidently a constant feature in every stage of growth after the shell becomes attached. The nature of this peculiarity was indicated by Briiurncs in the original diagnosis of the genus (Ann. Rept. Canadian Geol. Survey, 1857-58), and was demonstrated more fully by Professor Hatt, in the Twentieth Report on the Condition of the New York State Cabinet of Natural History (pp. 274-278, 1867). This area is underlaid by an internal shelf or diaphragm attached along its lateral margins, and having fully, or rather more than, the width of the median sinus. Through the space thus left between the shell and the internal dia- phragm, communication is afforded with the outside world. Mr. Joun Youne has called attention to the fact that in £. capewel/, the margins of the ex- ternal reticulated layer of the shell about the umbonal bare spot, are rough and ragged, the superficial hexagonal cells being without finish along these edges, suggesting therefrom, that the animal was attached to marine 32 MEMOIRS OF THE STATE MUSEUM objects by the substance of the shell, and afterward broken away from its attachment. (See Davrpson, General Summary, pp. 355, 356.) It is true that the anterior edge of this area may be rough and uneven, but the lateral edges appear invariably straight and diverge at an essen- tially constant angle. The latter represent the lines of attachment of the internal plate to the interior of the valve, and if the shell has been broken in detachment from foreign bodies, the fracture in these direc- tions has been guided by these lines, but on the unsupported anterior margin it has been rough and irregular. Upon the hinge-line of the ventral valve, there exists no aperture for the protrusion of the pedicle; by the peculiar development of the articulating processes of both valves, the entire cardinal margin is closed, and therefore the passage between the internal plate and the surface of the valve may have been for the use of this organ; or, it may be suggested, that as this space is rather too narrow and explanate for such a purpose, Ezchwaldia may have been attached by the substance of the shell, the internal shelf acting as a support to the strain upon the umbo, and a protection to the animal in case the shell were broken from its attachment. ANASTROPHIA INTERNASCENS, Hall, 1879 Pate III, Fics. 14-16 —— ——. Hall. Twenty-eighth Ann. Rept. N. Y. State Mus. Nat. Hist., p. 168, pl. 26, figs. 41- 49. 1879. —— ——, Hall. Eleventh Ann. Rept. State Geol. Indiana, p. 311, pl. 26, figs. 41-49. 1882. In tracing the development of this species, the principal feature to be noticed is that the elemental shell conforms with the type of an ordi- nary brachiopod, such as RAynchonella, that is, the dorsal valve, although somewhat the more convex, is smaller than the opposite valve, while in the mature state the dorsal valve is considerably larger and _ pro- jects beyond the beak of the ventral valve. It is the development of this SILURIAN BRACHIOPODA 33 character which constitutes the most conspicuous change in the shell in its growth from the young to the fully mature condition. SPECIFIC CHARACTERS Mature Form (plate 3, figs. 15, 16, 162). Shell ventricose. Out- line transversely subelliptical, sometimes nearly as long as wide. Ventral valve convex, depressed in front, forming a more or less defined sinus which carries four or five of the plications; beak short, acute ; area short, broadly triangular, usually not exposed. Dorsal valve gibbous, with the central portion elevated, frequently presenting a broad undefined median fold ; beak incurved under the beak of the opposite valve ; umbo prominent. Surface marked by about fifteen strong, simple, elevated, rounded or angular plications on the body of the shell, and smaller bifurcating plica- tions on the latera. Occasionally intercalated plications are present on the middle of the valves. The plications are crossed by fine arching striz of growth, which are sometimes aggregated, forming conspicuous concentric lines or varices of growth. Mature shells measure from 11 to 17 mm. in length, and from 12 to 19 mm. in width. The depth of the conjoined valves varies from 9 to 12 mm. Incipient Form (plate 3, figs. 14, 14a). The smallest shell observed has a length of 2 mm. and a width of 2.25 mm. The dorsal valve is slightly more convex than the ventral and is a little shorter. Eight rounded plica- tions are shown, five of which extend to the umbo of the valve.