@: 3 < ¥ A 7 MERISTINA NiTIDA, Hall, WHITFIELDIA MARIA, Hall, SprriFER Crispus, Hisinger, Saaee (AC SN SPIRIFER CRISPUS, var. SIMPLEX, Hall, SprrireR BICosTaTUs, (Vanuxem) var. PETILUs, Hall, SPIRIFER RADIATUS, Sowerby, < \RY OF DEVELOPMENTAL CHANGES, a ; 2 MANINEXPLANATIONS «2 2. «© . «. «©. I-VIII THE DEVELOPMENT OF SOME SILURIAN BRACHIOPODA By Joun M. Crarke and Cuaries E, BEECHER* 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 BarranpE, WaLcort, Forp and Matruew; Hyatt, Branco, Moyjsisovics 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 zoélogist 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 - . . a " oat al .. 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 some 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, Riynchonella stricklandi is a noticeable example, and it is- really the only 2 10 INTRODUCTION common species which has afforded no young shells. Waztfeldia 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 Watpron,, INDIANA Crantia siluriana, Hall, Crania setifera, Hall, Crania spinigera, Hall, Lingula gibbosa, Hall, Pholidops ovals, Hall, Orthis hybrida, Sowerby, Orthis elegantula, Dalman, Orthis subnodosa, Hall, . Orthis biloba, Linnzus, Streptorhynchus tenue, Hall, Streptorhynchus subplanum, Conrad, Strophomena rhombotdalis, Wilckens, Strophodonta profunda, Hall, Strophonella striata, Hall, Strophonella semifasciata, Hall, . Leptena transversalis, Dalman, Streptis waldronensis, Miller and Dyer, Chonetes nova-scotica, Hall, Chonetes undulata, Hall, Eichwaldia reticulata, Hall, . Pentamerus fornicatus, var., Hall, Anastrophia internascens, Hall, Rhynchonella neglecta, Hall, Rhynchonella acinus, Hall, Rhynchonella indianensis, Hall, Rhynchonella whiti, Hali, Rhynchonella stricklandi, Sowerby, Rhynchotreta cuneata, Dalman, One embryo. No young shells obtained. “ “cc Numerous inchoate specimens. “ce “ce No young shells obtained. ee ai “c “ Full series, showing development. “ee ae No young shells obtained. Full series, showing development. No young shells obtained. “ee ae One embryo, No young shells obtained. “ ia Young shells not rare. No young shells obtained. Young shells not rare. Young shells very abundant. Mature form abundant; no young shells obtained. Young shells common. > INTRODUCTION 11 Atrypa reticularzs, Linneus, : . Young shells abundant. Zygospira minima, Hall, : - : No young shells obtained. Celospira disparilis, Hall, . é : . Young shells common. Retzia evax, Hall, : i : : Young shells very abundant. Retzia sobrina, sp. n. - é . Young shells not rare. *Nucleospira pistformzs, Hall, A : Ss $f Meristella rectirostra, Hall, : ; . Full series, showing development. Meristina nitida, Hall, . F : - Numerous inchoate specimens. Whitfieldia marta, Hall, . ; ‘ . Incomplete series showing development. Spirifer eudora, Hall, . : f é No young shells obtained. Spirifer crispus, Hisinger, ‘ . Full series, showing development. Spirifer crispus, var. simplex, Hall, : a ee Spirifer radiatus, Sowerby, ; P - ce ES Spirifer bicostatus, var. petilus, Hall, 2 as ie 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 Pmenty- eighth Annual meron of oe New York State Museum *The mature charactors of this species are Ausuitiod so véacly, that the youngest teriad 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. Puitie 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. The same 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. ml ar DISCUSSIONS OF THE SPECIES CRANIA SILURIANA, Hall, 1863 PiatTeE 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, Dalman, 1827 Piate 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. Inthe 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 excesseof 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 Orthzs hydrzda, 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. hyébrzda 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. edegantula 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 Rhynchonella and Sperzfer. 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 J » : ‘ - 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 ventra/ 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 striz, 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 Orthzs 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 PiateE 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. hyérida than in that of O. e/egantula, and less in the ventral valve of the former than in that of the latter species. Thus O. hybrida 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 Haut (/oc. 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 Pate 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, Strophonella 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 striae. 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, 1@, 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 striz. 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. 3@ Stage. Length 2-20 mm.; shell radiatingly striated, and concentrically undulated. | gth 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 rhomboidatles 1st Stage, ad Stage. _ 3d Stage. 4th Stage. | Initial. Infantile. Adolescent, Mature. Size..............4 mm.—1 mm, in| 1 mm.—2 mm. in 2 mm.— 20 mm. in| 20mm.— 30 mm. in length, .4 mm.—) length, 1.5mm.— length, 2.5 mm.— length, 40 mm.— 1.5 mm. in width. 2.5mm. in width. 40 mm, in width. 50 mm. in width. Transversely semi- MOUs ¥chet Transversely semi- Longitudinally, Longitudinal] 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, ae SILURIAN BRACHIOPODA 2I Development of Strophomena rhomboidalis — Continued Pedicle-tube.... and _ concentri- cally undulate. 1st Stage. ad Stage. 3d Stage. 4th Stage. Initial. Infantile. Adolescent. Mature. Contour «».| Convex. Depressed convex.) Very slightly con-} Geniculate, making vex. the shell high] arched longitudi- nally. Dorsal valve....| Convex, concave) Concave,except on| Concave,except on| Flat or concave on on the margin; the umbo. the umbo. the body of the umbo prominent. shell; abruptly produced and curved upwards around the mar- gins. Ventral valve...) 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. Surface.........| Smooth. Radiatingly striate. Radiatingly striate| Entire surface, 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 Not exsert, full Nearly full height Obsolescent or ob- of the area. height of thearea.| of the area. solete. -Foramen.... .. Present, circular,| Present, circular. | Present, circular. | Usually present. elevated Dorsal callosity.| Small, grooved. | Small, grooved. | Larger, grooved. | Very large and deeply grooved. s Y 5 22 MEMOIRS OF THE STATE MUSEUM Among the mature shells, the greatest variation is to be found in the development of the anterior curtain, or geniculate and sloping marginal area of the valves. In some specimens this is so excessively déveloped, 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 striz are very uniform in their arrangement. No speci- mens have been noticed which are so strongly quadriplicate as those illus- trated by Mr. Davinson, 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 Atrypa reticularis. Strophomena rhomboidalis 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. —s 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. — is Hall. 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 youngést forms to full-grown specimens. SPECIFIC CHARACTERS Mature Form (plate 2, figs. 15, 15@,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 striz. 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, 14@). 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 1o 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, of, 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 suffi- 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, 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. Ven- 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 striae in each interspace; also crossed by fine irregular striz 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, and a 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. Tue 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 rhomboidalis and Strophonella striata develop in a parallel series until the individuals are a9 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 rhomboidalzs, 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 Streptorhynchus 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 STREPTIS WALDRONENSIS, Miller and Dyer, 1878 ‘ Piate III, Fics. 9, 10 Spirifera? waldronensis, Miller and Dyer. Contributions to Palzontology, 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 the 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, 96), 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 31 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 Prate III, Fics. 11-13 —— —, Hall. Twenty-eighth Ann, Rept. N. Y. State Mus. Nat. Hist., p. 169, pl. 26, figs. 50-54. — pis “all. 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 stnile 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 Briiincs 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 Younc | 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 Davipson, 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, Lzchwaldia 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 PLATE III, Fics. 14-16 — —, Hall. Twenty-eighth Ann. Rept. N. Y. State Mus. Nat. Hist., p. 168, pl. 26, figs. 41- —— ee tal 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 Rhyuchonella, 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, usuallysnot 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 strie 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, 142). 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. A short plication is intercalated in the middle and there is also a short one on each side of the valve. Ventral beak small and elevated, with a broad, triangular, open area below. DEVELOPMENTAL CHANGES The series of specimens selected to represent the development of this species contains fifteen normal individuals, varying from a length of 2 mm. toa length of 17mm. The proportions of length and width remain nearly constant throughout, the width being somewhat the greater. 5 34 MEMOIRS OF THE STATE MUSEUM In the smallest specimen, the depth of both valves is less than one-half the length of the shell. This relation gradually changes as the shell becomes larger and more convex, until, in mature individuals, the depth is equal to three-fourths or four-fifths the length of the shell, and in extremely obese specimens this ratio is often exceeded. The dorsal valve is more convex than the opposite valve, in all the stages of growth which have been observed, although in the elemental shell, the difference is scarcely perceptiblag while in the mature form it is a con- spicuous feature. This valve is also shorter than the ventral in specimens up to a length of about 7 mm. From 7 to 12 mm., both valves are of nearly equal length. Further growth causes the umbo of the dorsal valve to pro- trude beyond the beak of the opposite valve, and the beak is incurved and penetrates the area. It seems evident that if we had the true initial shell, the dorsal valve would be found not only smaller but less convex than the opposite valve. The fold begins to be apparent in individuals having a length of about 10 mm., and is expressed by the arching of the anterior margin. It does not sufficiently develop to become a characteristic feature and is more or less undefined, even in many full-grown specimens. The plications increase both by bifurcation and interstitial addition. The smallest number observed is eight, and this is gradually increased with the growth of the shell, until there are about fifteen principal plications on the body of the shell, and several smaller ones just below the cardinal extremities. The concentric striae are not often preserved and the plica- tions therefore form the only conspicuous character of the surface orna- mentation. The deltidial plates reach but a slight development, the triangular opening becoming completely filled by the incurved beak of the dorsal valve. SILURIAN BRACHIOPODA 35 RHYNCHONELLA acinus, Hall, 1863 PiaTE IV, Fics. g-11 —— —., Hall. Twenty-eighth Ann. Rept. N. Y. State Mus. Nat. Hist., p. 306, pl. 26, figs. 7-11. 1879. — —, Hall. Eleventh Ann. Rept. State Geol. Indiana, p. 306, pl. 26, figs. 7-11. 1882. Were Rhynchonella acinus a rare species, it might readily be confounded with the variety of 2. zzdianenszs, which bears but a single plication in the ventral sinus. It appears, however, to have been very prolific, and its abundance serves to emphasize its specific independence. The liability to confuse it with any of the associated species arises only among forms of immature growth. Beginning with a shell which is apparently in the actual initial stage, measuring 1.2x.8 mm., our series is very evenly consecutive up to maturity, when the average dimensions are 8x6 mm. SPECIFIC CHARACTERS Mature Form (plate 4, figs. 11-114). Shell small, longitudinally ovate, subattenuate toward the beak, and truncate in front. Cardinal margins long and rapidly sloping, extending more than half-way across the shell; sides flattened, slightly excavate. Valves subequally convex. Ventral valve full and rotund on the umbonal region, flattened at about the middle, thenceforward sinuate; beak ihcurved, but not pro- cumbent ; foramen generally concealed, or when slightly exposed, elongate or subtriangular. Dorsal valve more flattened in the umbonal region and in the middle, whence a low fold proceeds to the margin. Surface marked by low rounded plications. The ventral sinus bears a single plication which is generally faint, often nearly obsolete. On each side of the sinus are four plications, ‘those abutting on the cardinal margins being indistinct. On the dorsal valve, the low, flattened fold bears two plications which are the strongest upon the shell; these are accom- panied by three plications on each latus, making the whole number on this - 36 MEMOIRS OF THE STATE MUSEUM valve eight. No concentric growth-lines are apparent. Average dimen- sions 8x6 mm. Variations from the normal adult. Two plications sometimes occur in the sinus, and in such cases they are each stronger than the single sinal plication in the normal adult. The addition of the plication to the sinus increases the number in the fold to three, and the total number of plica- tions on the shell by two. Initial shell (Compare plate 4, figs. 9, 9a, 94.) Two individuals, one measuring 1.2x8 mm., the other 1.4x9 mm., apparently indicate the ini- tial stages in the growth of this shell. Neither of these examples has served well for illustration, on account of the lack of well-defined details, but they may be described as follows :—Attenuate, subspatulate. Ventral valve with erect, straight beak; cardinal area high, convex, with a promi- nent dorsum. Jorsal valve flattened or slightly sinuate. Features of the cardinal area not discernible; from analogy, the foramen would be triangular and unobstructed. In figures 9-94, which show a secondary stage of growth in the shell, the portion included within the first growth-line will represent very well the characters of the primitive shell. GENERAL DEVELOPMENTAL CHARACTERS The gradual incurvature of the beak and consequent concealment of the ventral foramen may be assumed from the foregoing. It harmonizes with the associated species of the same genus in the slight variation in the form and proportions of the foramen in consecutive stages of growth, as well as in the reversal of the embryonic fold and sinus to the mature sinus and fold. The plications of the latera seem to appear simultaneously after the first varix, as shown in the figures referred to, and their number does not change materially until maturity. The embyronic sulcus on the dorsal valve, correlate with the ventral dorsum in the primitive stage, is continued at maturity into the median sulcus separating the two plications of the dorsal fold. SILURIAN BRACHIOPODA , | 37 RHYNCHONELLA NEGLECTA, Hall, 1852 : PLATE IV, Fics. 3, 6-8 — —, Hall. Twenty-eighth Ann. Rept. N. Y. State Mus. Nat. Hist., p. 162, pl. 26, figs. 1-6. — eee, Eleventh Ann. Rept. State Geol. Indiana, p. 305, pl. 26, figs. 1-6; pl. 27, fig. 3. 1882. For a species so abundant as this in the Waldron fauna, the diagnos- tic features are.retained with unusual persistence within very narrow limi- tations. Unlike its associate, R. zxdzanenszs, which it almost equals in numerical representation, there are -no well-established and perduring variations from the normal adult form,-and our observations are therefore limited to an essentially unvarying phase. SPECIFIC CHARACTERS Mature Form (plate 4, figs. 8, 8a). Shell small, transversely sub- ovate; umbo scarcely prominent. Cardinal slopes long and _ flattened, rounding to the anterior margin which is nearly straight. Ventral valve with the umbo elevated and slightly incurved at the tip, overhanging an elongate subtriangular foramen. Umbonal region slightly convex, the convexity extending for one-third the length of the shell ; thence forward the shell is rapidly depressed medially to form a deep sinus, which makes a high quadrangular extension on the margin; lateral portions depressed. Dorsal valve with the umbo low and inconspicuous; apex concealed within the foramen of the opposite valve. The shell becomes rapidly ele- vated medially to form the fold, the latera being full and convex. Surface covered with regular, sharp and prominent plications, which do not vary in number at normal maturity, and which, in the growth of the shell, are increased only from the cardinal margins. Of these plications, the fold bears four, the sinus, therefore, three, and each of the latera, five, those nearest the cardinal margins being obscure. This makes in all for the 38 MEMOIRS OF THE STATE MUSEUM . ventral valve, thirteen, and for the dorsal, fourteen plications. Dimensions of an average example, length, width and depth, 9, 8 and 5 mm. A single individual presents the only important abnormality noticed, viz.: a failure to produce the requisite plications upon the latera, the dorsal valve bearing but five, and the ventral, six. Of these, three are on the fold, two in the sinus. It is interesting to notice that in the umbonal region the normal number of plications had been formed in their regular arrangement; their disappearance on the latera and irregular disposition in fold and sinus took place abruptly upon the completion of a growth-line 2 mm. from the apex. This is a marked instance of reversion after the assumption of certain adult features. Incipient Form (plate 4, figs. 6, 6a). The example with which our series opens measures .75x.5 mm. It is elongate subtriangular, with the ventral beak elevated and erect, the cardinal margins sloping for two- thirds the length of the shell; foramen triangular, slightly, if at all, en- croaching upon the apex, without deltidial plates, margins thin; dorsal beak rounded, inconspicuous. At one-third the distance from the apex to the anterior margin, fine thread-like plications appear, four upon the dorsal, and three (five?) upon the ventral valve. The median sulcus on the dorsal valve is broader and deeper than any other, forming the embryonal sinus, and is accompanied by a correlatively strong plication on the oppo- site shell. DEVELOPMENTAL VARIATIONS General Form and Outline. The form of the shell varies from dimensions in which the length is one-quarter greater than the width, to those of maturity when the width is slightly greater than the length, The depressed, subspatulate embryo eventually becomes convex and deep. The embryonal sinus and fold on the dorsal and ventral valves respectively, are never so prominent as in A. zwdianenszs, and soon become lost, the SILURIAN BRACHIOPODA 39 former in a sulcus, and the latter in one or more sulci upon the reversed fold and sinus of maturity. Beak and Foramen. The erect and acute beak of the elementary stages of growth, becomes, at maturity, but slightly iacurved, and never procumbent on the dorsal umbo. The foramen, at the outset triangular, subsequently has its margins thickened, and develops small and obscure deltidial plates at its base, which at maturity leave the foramen elon- gate and not circular. In respect to these features, the development of the species is identical with that of A. zxdzanensis. Plications. In the first observed stadium, only the umbonal area is smooth, and from the analogy of A. zxdanensis, it would appear that the initial growth-stage yet fails us. Ata size of 2.5x2 mm., the number of plications has increased from four to ten on the dorsal, and from three (five?) to eleven on the ventral valve, and this, added to a pair of ex- tremely obscure plications near the cardinal margins, is the normal number for maturity. RHYNCHONELLA WHITH, Hall, 1863 PLATE IV, Fics. ft, 2, 4, 5 —— —, Hall. Twenty-eighth Ann. Rept. N. Y. State Mus. Nat. Hist., p. 164, pl. 26, figs. 23-33. 1879. — —, Hall. Eleventh Ann. Rept. State Geol. Indiana, p. 307, pl. 26, figs. 23-33. 1882. Like Rhynchonella neglecta, this species is subject to very slight vari- ations at maturity, and its specific expression is well marked, but a certain embarrassment attends the first endeavor to separate the immature individu- als from those of allied species. This, however, disappears with a careful eye properly estimating the essential characters of the species. The earliest stage of growth we have found measures 2.75 mm. in length by 2 mm. in breadth, and from this size upward to that of 13x13 mm. all variations are present. 40 MEMOIRS OF THE STATE MUSEUM SPECIFIC CHARACTERS Mature Form (plate 4, figs. 2, 2a, 26). _ Shell transversely sub- elliptical ; length and width about equal. Ventral valve shallow ; beak high, acute, somewhat attenuate, with the apex slightly incurved, but not concealing the triangular unclosed foramen which reaches entirely across the cardinal area. At its apex the foramen encroaches slightly upon the umbo, and is narrowed somewhat toward the base by the imperfectly developed deltidial plates. A median depression makes its appearance at about one-third the distance from the umbo to the anterior margin, and soon develops into a deep sinus with sharply sloping sides. Dorsal valve deeper and more gibbous; beak inconspicuous, and incurved beneath the ventral foramen. A strong median fold corre- sponds in development with the median sinus of the opposite valve. Surface marked by strong, simple, subangular plications, invariably two upon the fold and one in the sinus, with six on each of the latera, making thirteen on the ventral, and fourteen on the dorsal valve. Of these, the plications near the cardinal margin are low and incipient, but the full number becomes permanent early in the history of the individual. Faint concentric growth-lines are sometimes visible. Dimensions of average adult 11x11 mm. Abnormalities at maturity. The variations from the normal ma- ture form are, as far as observed, wholly due to continued internal growth after individual maturity has been attained, and this is to be regarded as the concomitant evidence of senescence. There may be either a margznal thickening, which gives the shell a truncate appearance, or a general z¢ernal thickening, making the shell unusually gibbous, and forcing the ventral beak over upon the dorsal umbo. Incipient Form (plate 4, figs. 1, 1). The youngest individual observed measures 2.75x2 mm. ; outline subovate, valves regularly rounded, SILURIAN BRACHIOPODA | 41 the ventral being the more convex. Ventral valve with an erect, straight beak; apex acute, cardinal margins sloping rapidly forward, and slightly excavate. Foramen simple, triangular, free from deltidial plates, encroach- ing at its apex slightly upon the umbo; foraminal margins somewhat thick- ened, Dorsal beak erect but inconspicuous, full and rounded. Dorsal valve depressed anteriorly along the median line, this depression correspond- ing with the broad and low dorsum of the opposite valve. Surface of each valve marked by eight single, rounded plications, which extend two-thirds the distance from the anterior margin of the beak, leaving the circumbonal area smooth, DEVELOPMENTAL VARIATIONS General Form and Outline. As growth advances, the development is more rapid transversely than longitudinally, and, consequently, the subo- vate incipient shell becomes, at maturity, broadly transverse. The prominent dorsum of the ventral valve in the embryo, is manifest at maturity only in the rounded and prominent beak, and the embryonal sinus in the dorsal valve becomes so thoroughly obsolete at maturity as to be unnoticeable. In stages of development between the dimensions 3.5x3 mm. and 6x5.5 mm., the ventral valve still retains a slightly greater convexity, but the anterior margin is entire. . Beak and Foramen. The erect and straight beak of the incipient shell becomes slightly incurved toward maturity, but the cardinal area re- mains high, exposing the triangular foramen at all stages of growth. Del- tidial plates make their appearance early, but never develop sufficiently to meet and inclose the pedicle-aperture, a feature indicative of arrested de- velopment, and equally true of the other members of the genus here discussed. . Plications. The fact that the eight plications on each valve of the incipient shell do not reach the umbones, indicates that the initial shell may have been smooth, as we have shown it to be in 2. zxdzanensis. The 6 42 MEMOIRS OF THE STATE MUSEUM subsequent addition of plications takes place slowly and from the cardinal margins. RHYNCHONELLA INDIANENSIS, Hall, 1863 Pate III, Fics. 17-28 —— ——, Hall. Twenty-eighth Ann. Rept. N. Y. State Mus. Nat. Hist., p. 163, pl. 26, figs. 12-22. 1879. ————, Hall. Eleventh Ann. Rept. State Geol. Indiana, p. 306, pl. 26, figs. 12-22; pl. 27, figs. 4-6. 1882. Rhynchonella tndianensis is, beyond a doubt, the most prolific species in the rich fauna of the Waldron beds, and by virtue of this fact, we have been enabled to ascertain the developmental phases through illustrative series of exceptional completeness. It is noteworthy that the mature shell of this Rhynchonella presents variations from the adult type, which are so great that in a certain sense they might be regarded as passing the limitations of specific identity ; however, the general form and expression of the shell are characteristic, so that, in spite of these variations, no confusion with allied species of the same fauna can arise, nor need there be any hesitation to assign to the different forms a varietal significance only. Probably ten thousand individuals of this species have passed under our observation, and of this large number, fully one-half have been immature forms. SPECIFIC CHARACTERS Normal Mature Form, containing two plications in the sinus of the ventral valve (plate 3, fig. 21). Shell subtriangular or broadly ovate ; length nearly equal to, sometimes slightly exceeding the width, Umbo prominent, subacute; cardinal slopes extending one-half the length of the shell, and flattened. Ventral valve depressed convex, rounded at the beak; apex pointed and slightly incurved, exposing beneath it the elongate, narrow foramen and the inconspicuous deltidial plates. Dorsum for the first one-third the length of the shell rounded, thence, anteriorly, gradually becoming de- SILURIAN BRACHIOPODA 43 pressed. The sinus thus formed bears two strong, rounded plications which are of later origin than the pair which forms its lateral boundaries, The latera bear each three plications with traces of a fourth, making eight (ten) on the entire surface of the valve. Dorsal valve somewhat deeper than the ventral, flattened above, depressed near the beak along the median line (embryonal sinus), thence forward, becoming gradually elevated into a fold which bears three strong rounded plications. Four similar plications are discernible on each of the latera, making in all eleven plications on the entire valve. Umbo incon- spicuous, apex concealed within the foramen of the opposite valve, Con- centric growth-lines obscure, or absent. Average dimensions 12x12 mm. These are assumed as the normal characters of adult growth on account of the great predominance of specimens bearing ¢wo plications in the ven- traf sinus. Variations from the Normal. A. Forms with one plication in the ventral sinus. This variation does not attain quite the size of the average normal adult, but retains the same proportion of length and breadth (size 1ox1o mm.). ‘The surface bears ten plications on the dorsal and nine on the ventral valve. In this form, the embryonal sinus, visible on the earlier por- tion of the dorsal valve, is distinctly continuous with the strong sulcus separating the two plications on the fold in the later and marginal portions of the valve. This variation is not of uncommon occurrence, and immature individuals in various stages of development prove that it is a well-estab- lished genetic difference, and not merely an occasional monstrosity. B. Forms with three plications in the ventral sinus. The size and pro- portions of the normal are retained in this variety, but the shell bears usually three, sometimes four plications on each of the latera, making ten (twelve) plications for the dorsal, and nine (eleven) for the ventral valve. This form is of comparatively rare occurrence, and is not often noticed in an immature stage of growth. 44 MEMOIRS OF THE STATE MUSEUM C. Forms with four plications in the ventral sinus. This variation is met with very infrequently, but two individuals having been obtained. While agreeing in size with the normal adult, the crowding of the sinus with pli- cations tends to obliterate both it and the fold upon the opposite valve. Both individuals show the interesting fact that upon the dorsal valve where the fold bears five plications, i. e., four sulci, the embryonal sinus is contin- uous with the ¢/zrd of these sulci, in-one instance numbering from the right, in the other, numbering from the left. Of the five plications which are thus separated into groups of three and two, it is noticeable that the outer member of the group of three is both less elevated and shorter than any~ other upon the fold. Monstrous Forms. The sole evidence of monstrous growth that has been observed is an asymmetrical development of the plications upon the dorsal fold. Examples bearing three plications upon the fold, in rare instances have one of the plications very large and two quite small, making one broad and one narrow sulcus upon the fold. The phenomenon may be due to the strongly developed tendency of the embryonal sinus to maintain its continuity with a median sulcus even at the expense of the symmetry of the shell. ; Initial Shell (plate 3, figs. 17, 17@). The initial shell in our series of Rhynchonella indianensis measures .65 mm. in length by .54 mm. in width, It is broadly ovate or subpyriform in aspect, convex posteriorly, and depressed toward the anterior margin. Ventral valve with the umbo prominent, the beak elevated and erect, with the apex rounded; cardinal margins rapidly sloping. Foramen subtriangular, apical portion broader than usual in the incipient stages of plicate shells ; margins not thickened ; deltidial plates absent. Dorsal valve with a rqunded, inconspicuous beak. Surface of both valves quite smooth. A median depression is noticeable on the dorsal valve near the anterior margin, making this margin sinuate. This embryo is the smallest that has been found for any of the series SILURIAN BRACHIOPODA 45 of Rhynchonellas, and not only on account of its minuteness, but also from the entire absence of plications on its surface and from the elementary character of the cardinal area, we are inclined to regard it as the actual ele- mental or initial shell. . DEVELOPMENTAL VARIATIONS General Form and Outline. The adult variations from the normal, noticed above, seem to be in most instances, and probably would prove to be in all, preceded by well-defined embryonic series leading up to them. This must be the case, as the character of these variations, i. e., variation in the number of plications on the median portions of the shell, is such that they cannot be assumed after the attainment of the adult condition, as is possible’in certain other forms of variation. But it is not to be assumed that the conformation of the embryo which eventually pro- duces any of these results, manifests them in the earliest stages of the growth of the shell, rather, that the shells, under whatsoever variations at maturity, all have the same unspecialized starting point. Hence, the fact that some of these variations have not shown a complete series of immature ' stages must be due to the insufficiency of our material, rich as it has been. Limiting our considerations now to the normal form with ¢éwo plications in the ventral sinus, we notice that the initial shell is smooth, and obcordate in outline, with beak erect, while the mature shell is strongly plicate, strongly ovatewand--with the beak sharply incurved. The transition. from one extreme to the other is through stages of growth between the -limits -65x.54 mm. (initial) and 12x12 mm. (average adult), In growth-stages below 7x5 mm. dimensions, the shell is very depressed-convex, the dorsal valve up to about this point, retaining a low, broad, median depression, accompanied by a similarly low and broad median elevation on the opposite valve. It is not always possible to determine with accuracy how many plications are carried by this embryonic fold and sinus, on account of its not being well limited, but their eventual reversion, in the adult shell, into 46 MEMOIRS OF THE STATE MUSEUM sinus and fold, respectively, marks the feature as an interesting one, to which we call attention more at length in the description of the species Rhynchotreta cuneata and Atrypa reticularis. Rare instances occur of individuals assuming all the characters of maturity before attaining a length of 6 mm., and from this point upward to the normal size for adult growth, mature dwarfs are frequently found. Beak. In the initial shell, the beak of the dorsal valve is rounded and inconspicuous, and so remains in all stages of growth. In the opposite valve, the beak is at first high, erect but not acute, the cardinal margins sloping abruptly, and with increasing age the beak becomes fuller, more and more incurved at the apex, but is never closely procumbent upon the dorsal umbo, as is the case in maturity with most of the plicate species here described, Foramen. At the outset the pedicle-aperture is narrowly subtrian- gular, reaching to and encroaching upon the apex, free of deltidial plates and with the lateral margins unthickened, i. e., elemental in every respect. In the second stage. of growth (after the appearance of plications on the surface, dimensions 1.5x1.1 mm.), the apertural margins have become thickened, and directly thereafter, the deltidial plates begin to develop, gradually narrowing the aperture at the base. The symphysis of these plates with the valve is marked by distinctly elevated lines. In maturity, the deltidial plates have developed sufficiently to completely close the lower part of the aperture, coming together behind the beak of the dorsal valve, and giving to the foramen an elliptical outline constricted toward the apex, where it encroaches upon the umbo, The fact that the development of the foramen is thus interrupted before it reaches the circular outline normal to the adult of most paleozoic species, indicates an embryonic character in the adult, and, therefore, a subordinate taxonomic position for the species. Plications. These appear only after the first stage of growth is passed and after the first growth-line has been formed. As in Reézta evax, SILURIAN BRACHIOPODA 47 they appear over the entire surface of the shell below the growth-line all at _. once, and from this stage onward to maturity, no increase is made in the number, except by intercalation along the margin of the fold and sinus. RHYNCHOTRETA CUNEATA, Dalman, 1827 var. AMERICANA, Hall, 1879 Prater IV, Fics. 12-22 —— —— — Hall. Twenty-eighth Ann. Rept. N. Y. State Mus. Nat. Hist., p. 167, pl. 25, figs. 29-38. 1879. —— —— —, Hall. Eleventh Ann. Rept. State Geol. Indiana, p. 310, pl. 25, figs. 29-38. 1882. The individuals of this species do not so readily separate into three groups of long, normal, and broad forms, as do those of Rhynchonella neg- lecta, Retzia evax, Meristina nitida, and others. This seems to be due to the uniformity in the number of plications, and also in the number carried on the fold and sinus. The long and broad varieties do exist, however, but are of such infrequency as to suggest that they are not genetic variations from the typical form occurring in this locality. The specimens from the Wenlock shales of Dudley, show a consider- able variation from their American congeners, in having more numerous plications, of which a greater number is raised on the dorsal fold and depressed in the ventral sinus. In other respects, it is believed that the description here given, of the development of the shell, will apply to the British form. Rihynchotreta cuneata, although considered as abundant in the mature state, does not approach in the number of young specimens, RAyuchonella ; whitit, R. neglecta, R. indianensis, Retzia evax, Meristina nitida, Spirifer crispus, Sp. crispus, var simplex, Atrypa reticularis, Orthis hybrida, and O. elegantula, The entire numberof young individuals examined is about one hundred and fifty, ranging in size from 8 mm. to 1.5 mm. in length. - The mature forms average about 17 mm. in length. 48 MEMOIRS OF THE STATE MUSEUM In the several series selected from the material at hand, it is evident that the shell assumed the characters and form of maturity when reaching a length of about 1omm. At this period of growth, the fold of the dorsal valve becomes elevated, and the sinus of the ventral valve. depressed (fig. 15, plate 4). Previous to this stage, the dorsal valve is depressed — and transversely concave, and the plications of the opposite valve are raised along the median line of the shell. SPECIFIC CHARACTERS Mature Form (plate 4, figs. 14, 14a, 148, 22, 222). Shell triangular, cuneiform, widest across the pallial region. Length equal to about twice the depth of the valves. Beaks compressed laterally, attenuate and pointed. Ventral valve moderately convex, subangular along the latera, marked by a deep sinus, which commences near the middle of the length, and becomes very marked in front, depressing three plications, of which the middle one is detruded more than the others. Dorsal valve convex, gibbous in the posterior part, with the latera elevated and subangular ; marked in front by a prominent fold which begins near the beak as a depression carrying four plications, of which the two central ones are usually much more elevated than the other pair. Area high, closed by two triangular deltidial plates. Perforation of the ventral beak ovate, truncating the apex, and limited below by the del- tidial plates. Surface marked by from eight to ten strong, angular plications, which are crossed by very fine, regular, sharp, concentric striae. Mature specimens usually measure from 10 to 17 mm. in length. Incipient Form (plate 4, figs. 12, 12a). The youngest shell detected has a length of 1.5 mm., is flattened, and nearly circular in outline. The dorsal valve is depressed in the middle, and carries four plications. The beak of the ventral valve is broadly triangular, exsert,-and elevated, with a triangular, open area without deltidial plates. SILURIAN BRACHIOPODA 49 DEVELOPMENTAL CHANGES Contour. In the earliest stages yet noticed, the shell is nearly cir- cular. Ata length of 2 mm., it is broadly oval, and at 2.5 mm., it is ovate. The beak in the next advanced stage is more elongate, and when the length of 4 mm. is reached, the shell has a decidedly triangular or cuneate form, which becomes more pronounced up to maturity. All the young and adolescent shells are depressed, the characteristic fullness of the valves not being developed until after the assumption of the features of maturity, and when the shell approaches its normal size. Fold and Sinus. The smallest individual shows a slight depression in the dorsal valve, co-existing with the plications, beginning about one-fifth the length of the shell in front of the beak, widening rapidly, and becom- ing more defined upon approaching the margin. The latera are nearly flat. The depression, or sinus, becomes more pronounced with the advance in growth, until a length of 4.5 mm. is attained. After this period, the four bottom plications gradually elevate, the sinus grows shallower, and the front margin of the conjoined valves becomes nearly straight. Upon reaching a length of 9 mm., the two central plications are sufficiently elevated to define the fold, which is hereafter the principal feature of the dorsal valve. The development from this point to full-grown individuals is prin- cipally directed to reaching a maximum prominence in the fold, and increas- ing the shell by increment on the lateral margins of the valves. The development of a sinus in the dorsal valve, its subsequent oblit- eration, and the final elevation of the plications into a strong median fold, are shown in figures 15, z—zo of plate 4, in which the undulating lines represent the anterior junction of the valves. Beak. The apex of the dorsal valve is strong and pointed, and is visible in all specimens up to a length of about 14 mm. After this stage, the shell becomes obese, and the consequent greater inclination of the beak, forces it into the foraminal cavity, where it becomes hidden by the deltidial plates. 7 50 MEMOIRS OF THE STATE MUSEUM The ventral valve is uniformly convex in all incipient specimens. The sinus develops at the same period, and in conformity with the fold of the opposite valve. The beak of the initial shell is broadly triangular, perfo- rate at the apex, and directed outwards. It gradually becomes narrower and less oblique with advancing growth, and lies in the axis of the shell in full- grown specimens. The initial perforation is a small truncation of the beak, confluent with the open area below. (.See figure 16, plate 4.) Surface ornaments. The prevailing number of plications is eight, al- though it varies from seven to ten in some specimens. The entire number appears at an early period of growth, and in this respect, the species offers a marked difference from some of the forms of RAynchonella already con- sidered, in which the plications increase by pairs. In a specimen 1.5 mm. long, they first appear at about one-fifth the length of the shell from the beak. Four plications are included in the depression of the dorsal valve in the incipient stages, and the two central ones finally become elevated, forming the fold in the full-grown shell. Upon approaching maturity, three of the plications in the ventral valve are depressed, the middle one ulti- mately much more than the others, forming the single strong plication at the bottom of the sinus. No concentric striae are shown on the initial shell of our series. Ina specimen 3 mm. in length, these begin to develop over the outer third of the surface, as shown in figure 13, plate 4. Cardinal area. The foramen is at first a broad triangular opening, wider than high, with sharp margins, and truncating the beak of the ventral valve. The lateral margins are thickened ina specimen 3 mm. in length (plate 4, fig. 13), and the height and width of the area are equal. These pro- portions of height and width are preserved to maturity, although in some specimens the area is higher than wide. No deltidial plates have as yet appeared, but in the next stage, including individuals having a length of 4.5 mm., there are two narrow deltidial plates developed from the sides of SILURIAN BRACHIOPODA 51 the foramen (plate 4, fig. 18). A specimen 5 mm. in length shows the still further increase in the size of these plates, although they do not come in contact, but leave an oval opening extending from the ventral beak down to the beak of the dorsal valve (plate 4, fig. 19). The increase in the growth of the deltidial plates along their inner margins brings them in con- tact under the dorsal beak, in specimens having a length of about 7 mm. (plate 4, fig. 20). Further growth truncates their inger angles, thus short- ening the deltidial opening. In individuals about 12 mam. long (fig. 21), the opening extends but little more than half the length of the area, and the lower margin of the opening is thickened and slightly deflected. Fully matured forms, having a length of from 15 to 17 mm., have a perforation less than one-half the height of the area, which truncates the beak more strongly than in younger shells, and the deltidial plates show a defined thickened area below the perforation, often extending to the dorsal beak (plate 4, fig. 22). Variations. As already stated, the elongate and broadly flabellate shells appear to be, in this species, neither common nor genetic variations. Among the extraordinary developments are specimens with duplicate pli- cations in the sinus, and one showing but seven plications on the shell. Another individual has the initial shell strongly defined by a varix of growth, and shows on this portion ten plications, but in the subsequent growth, only eight plications are continued, these alternating at the varix with those of the embryonic shell. ATRYPA RETICULARIS, Linnzus, 1767 Prate VI, Fics. 12-20 — -—, Hall. Twenty-fourth Ann. Rept. N. Y. State Mus. Nat. Hist., p. 162. 1879. — —, Hall. Eleventh Ann. Rept. State Geol. Indiana, p. 304. 1882. The abundance of this well-known species at Waldron has afforded the means of studying its developmental stages with very satisfactory results. All the individuals, from the earliest observed stage upward, agree in con- 52 MEMOIRS OF THE STATE MUSEUM tour, there being no such variation in this respect as has been noticed in some other species (e. g. Retzta evax, Meristina nitida) in which appear deviations from the normal, producing a long type and a broad type. The youngest individual detected has a length of 2.25 mm. and a width of 2mm., though this may not be regarded as the initial shell on account of the presence of partially developed deltidial plates. From this stage of growth to maturity, the material has afforded every variation in size and structure. SPECIFIC CHARACTERS Mature Form (plate 6, figs. 13, 13a, 20, 202). Atrypa reticularis is so widely distributed, historically and geographically, in paleozoic faunas, and is so familiar to paleontologists, that a detailed description here of its mature form is unnecessary. It is sufficient to remark that the prevailing expression at this locality does not precisely conform to the type of A. reticularzs, but is more nearly that variety described by Professor Hatt (Paleontology of New York, Vol. 2, p. 271, 1852) under the name Atrypa rugosa. This is evident from the development of the varical lamel- la, which, over the plications, are infolded into nearly tubular processes, sometimes produced at a strong angle from the shell to a length of a milli- meter or more. On the varices, the plications are covered by fine concentric wrinkles. The average size of mature individuals, 25x25 mm., is less than that usual to the species, when occurring in later, especially Devonian, faunas. Incipient Form (plate 6, figs. 12, 12a, 15, 15@). The initial shell, or the actual inchoate period in its formation, is not known to us. The in- cipient shell of our series is very small, and can be but a few removes from the initial stage. As just observed, it measures 2.25 mm. in length by 3 mm. in width, and shows but two concentric striae, or growth-varices, with a correspondingly slight development of the deltidial plates, so that we are inclined to regard this shell as but two stages advanced from the actual SILURIAN BRACHIOPODA 53 inception of the shell. The test is flat, both valves being shallow and depressed toward the anterior margin; the ventral beak high and erect, the dorsal beak inconspicuous and rounded. The foramen, which is undoubtedly triangular in the initial shell, has, at this stage, its basal angles slightly rounded by the faintly developed deltidial plates. The plications are six in number on the ventral, and five on the dorsal valve, the middle one of the latter not reaching so far toward the beak as those adjoining it, and toward the anterior margin being depressed below the lateral portions of the shell. General outline subcircular or subpentagonal, as in the full- grown shell. DEVELOPMENTAL VARIATIONS General Form and Outline. Embryos of less than 3 mm. in length are more nearly circular in outline than at any subsequent period of the existence of the individual. Directly thereafter, the hinge-line represents the greatest diameter of the shell, and the outline becomes subpentagonal, a feature which is more apparent in young individuals having between 3 and 10 mm. length, as the increasing rotundity of ‘the shell with the approach of maturity has a tendency to obscure, in a measure, this out- line. At the earliest stage studied, the dorsal valve is distinctly depressed along the median line, forming a sinus containing a single plication which does not reach to the beak (plate 6, fig. 142). This,sinus gradually becomes shallower, and the plications are increased by intercalation until they are three in number (fig. 144). In the next stage, all evidence of a sinus upon the anterior margin disappears, leaving it even and straight as shown in figure 14c ; then the anterior edge becomes reflexed, showing, in subsequent stages of growth, a fold where there had previously been a sinus, this fold bearing at first three, then five, and eventually, in the mature individual, seven plications (fig. 14d, ¢, f). This very remarkable reversion of the fold and sinus relatively to the valves which bear them, is also seen in the species Rhynchotreta cuneata and, in all adult specimens, may be clearly traced upon the earlier or embryonal portions of the valves. * . 54 MEMOIRS OF THE STATE MUSEUM Beak. In the first stage, the ventral beak is high and slightly re- supinate, exposing the foramen in an inclined plane. It gradually shortens and becomes erect, and when the shell attains a length of 8 mm,, it is bent forward, the cardinal area being slightly incurved. Thereafter, the inflec- tion of the area increases, concealing first the deltidial plates, and finally — the foramen, until, in maturity, the beak lies appressed upon the embryonal sinus of the dorsal valve. Foramen. In the initial shell, this is undoubtedly triangular and free from deltidial plates. With the starting point of our series, however, plates have begun to develop, thus narrowing the pedicle-aperture, and rounding its basal angles. With the growth of the plates more rapidly along the lower portion of their inner edges, the foramen shortens quickly, while narrowing but slowly, assuming in the second stage (fig. 16), a lanceolate, in the third stage (fig. 17), an oval, and in the fourth stage (fig. 18), a broadly circular outline. In the last two of these stages, the deltidial plates have come in contact with’ each other above the apex of the dorsal valve, and the pedicle-aperture itself has, from the second, if not from the first stage in the series, encroached upon the apex of the valve, so that, as it attains a circular outline, one-half its periphery is formed by the substance of the valve itself, and the other half by the deltidial plates. From this stage upward, there is no apparent change in the actual dimensions of the foramen, and, therefore, with the growth of the shell it becomes relatively much smaller. It appears, however, that with the incurving of the cardinal area and the concealment of the deltidial plates, the foramen becomes more and more inclosed by the apical portion of the valve, and it may be that actual contact with the deltidial plates in the last stage of development is lost. In this final stadium, with the procumbent position of the ventral beak upon the dorsal valve, the plane of the foramen is parallel to the sur- face of the dorsal valve, and the aperture is therefore lost to sight, or visi- ble only at its upper edge. SILURIAN BRACHIOPODA 55 Plications. Of the five and six plications visible upon the youngest member of the series, three or four appear to exist on that portion of the shell included within the earliest growth-line, i. e., presumptively, the initial shell, and they increase by intercalation until, in the adult, the average num- ber is about sixty for each valve. Concentric lines of growth follow each other with unusual rapidity, particularly in early life Summary. Atrypa reticularis, in the development of its beak, fora- men, and deltidial plates, is in essential harmony with the other uniforami- nate shells here discussed. The reversal of the fold and sinus is an interest- ing but not unique feature, and by the time it has been completely effected many of the characters of maturity have been assumed. From the degree of exposure of the foramen, we judge that the animal remained attached by its pedicle up to adult growth, but with full maturity and the approach of senility, the pedicle must have become atrophied and the animal set free. Retzia EvAx, Hall, 1863 Pate V, Fics. 1-9 — —-, Hall. Twenty-eighth Ann. Rept. N. Y. State Mus. Nat. Hist., p. 160. 1879. — —, Hall. Eleventh Ann. Rept. State Geol. Indiana, p. 302. 1882. In this species, the superficial features have been found of much more permanent character than is usual in the plicate brachiopoda from this horizon. Not far from three thousand individuals have been-examined, and these show a variation in size from a length of 1 mm. and a width of .8 mm., to a length and width of 25 mm. Throughout the younger stages in this series of variations, the feature of primary importance in distinguishing the embryo of this from those of other species, notably Retzza sobrina Rhynchonella indianensis, and Rhynchonella whitz2, is the sinus which exists on both ventral. and dorsal valves; and of much accessory value, the com- paratively slight variation in the number of the plications on the lateral portions of the valves. These features will be presently adverted to more at length. 56 MEMOIRS OF THE STATE MUSEUM SPECIFIC CHARACTERS Mature Form (plate 5, figs. 2, 2a). Shell ovate, generally longer than wide, both valves almost evenly convex, and of about the same depth. Anterior margin generally slightly emarginate, on account of the median sinus which exists on both valves. In rare instances, a low. median fold is developed near the margin of the dorsal valve. Ventral valve with the beak much elevated above the dorsal, and in- curved, so that the plane of the foramen is parallel to the axial plane of the shell. Foramen circular, or slightly subtriangular; deltidium generally obscure on account of the infolding of the beak, but showing the triangu- lar deltidial plates. Dorsal valve regularly arcuate, except at the posterior extremity, where the beak is closely incurved beneath the ventral umbo. The median sinus usually carries from three to five plications, but sometimes becomes filled up, in advanced growth, by the crowding of these plications. Ventral valve with a well-marked sinus, generally bearing three plications. The sinal pli- cations on both valves take their origin in front of the beak, and are of interstitial growth, a fact which does not hold true for any of the other plications. The surface is marked by from eight to twelve rounded, con- tinuous plications on each side the sinus of either valve, all of these ex- tending to the beak, with the possible exception of the more obscure ones on the cardinal slopes. Only in rare instances and abnormally, do these plications increase by interstitial addition. Imbricating lines of growth are often present, and fine concentric stria are sometimes discernible. The mature individuals of Retzéa evax divide themselves into three groups, based on their relative proportions : (a) Normal form, in which the length and width are equal. (4) Long form, in which the length is greater than the width. (c) Broad form, in which the length is less than the width. In frequency of occurrence, the form (6) almost equals the normal, SILURIAN BRACHIOPODA 57 while the form (¢) is more rarely met with. The form (4) is also of remark- able persistence, and starts so early in the life of the individual as to sug- gest a distinct genetic impulse. Variations from the normal development. These are to an unusual degree very slight, and may be classed as follows : Obesity, which apparently occurs only when normal full growth has been attained. _A tendency to asymmetry in development of the sinal plications. A marked illustration of this is afforded by an individual which, in repairing . an injury to its shell, has abruptly developed six plications on one side of the sinus, in continuation of three and to correspond with three on the opposite side. The absence of plications in the sinus. This is a feature of rare occurrence, and is undoubtedly an infantile character retained in later stages of growth. A single individual of immature growth affords an illustration of a peculiar abnormality, indicating a reversal in the growth to an embryonic condition. This shell (plate 5, figs. 3, 3@) has grown to a certain size and normally developed its plications, but an abrupt period has been placed to their development, and over the entire anterior portion of the individual, in front of a stout varix, the sur- face of the shell is almost smooth. This is the exact counterpart of that mode of growth, to which attention is called under other species, where -the smooth embryonic condition of the shell seems to be prolonged for more than the usual period of immaturity, and the mature features are thereupon abruptly developed after the formation of a sharp growth-line. DEVELOPMENTAL VARIATIONS Our series of individuals illustrating the embryological changes in this species is so complete as to show by almost imperceptible gradations the entire chain of development from very near the starting point up to matur- ity. This series begins with an individual measuring 1 mm. in length and 8 58 MEMOIRS OF THE STATE MUSEUM .8 mm. in width, and at this stage of growth, the incipient shell has mani- festly not received much increment. That this, however, is not the actual primitive shell seems proven by indications of two very indistinct con- centric growth-lines, and by the presence of faint radiating plications near the anterior margin, between the second growth-line and the margin itself. It is very probable that the incipient shell consisted of that portion of the individual (plate 5, fig. 1) lying within the first growth-line, and as this would make its size about .5x.4 mm., this fact in itself is sufficient apology for our not having detected the earliest stage of its development, even if other causes had permitted its preservation. Beaks. In all normally developed individuals less than 5 mm. in length, the beak of the ventral valve is erect and exsert. At about this stage of growth, a tendency to apical incurvature is manifested, which increases up to maturity, when, under normal development, the entire umbo is evenly incurved, concealing the deltidial plates and often much of the foramen. On the dorsal valve, the beak is quite obscure in the young- est forms, and in later stages of growth is concealed beneath the deltidium or incurved beak of the opposite valve. Foramen. This appears first as a simple triangular opening, its apex reaching to, but nof truncating the apex of the umbo, and it is re- tained in this condition until the shell attains a length of at least 3 mm. of normal growth. At this age, the deltidial plates begin to form, making their first appearance as two minute triangular lamine, taking their origin in the basal angles of the foraminal triangle; and giving the foramen a lanceolate outline. By increments to their internal edges, these plates presently come in contact with each other, truncating the interior basal angle of each, the plates being, from this period onward, in progressive symphysis. The incre- ments to these plates are made more rapidly at and about their interior angles, and asa result, the foramen assumes successively an elliptical, an SILURIAN BRACHIOPODA 59 oval, and a circular outline. _The circular curve of its upper extremity is caused by a slight encroachment upon the beak, and this in mature age is so considerable that the primary or incipient shell is undoubtedly wholly absorbed. The plane of the foramen remains, except in rare instances, always vertical, although the deltidial plates become slightly bent by the incurving of the beak. A striking exception to this rule is represented on plate 5, figure 9, where an individual which has reached early maturity shows the senile feature of a beak incurved to such a degree as to almost obscure the foramen. On approaching maturity, the deltid- ial plates appear to become anchylosed along their exterior edges, with the shell itself, the line of union being marked with a low ridge, and we have never seen them displaced by any distortion of the shell, as so often occurs in Calospira disparilis. Sinus. As already noticed, the sinus, in the elementary shell, begins as a low, smooth depression, equally strong on both valves, and extending almost to the beak. It gradually becomes filled by the radiating plications, which appear first at the sides, and increase toward the middle, never becoming, normally, more than six. None of these plications reach the apex of the shell. Plications. On the latera of the shell, these seem to appear simul- taneously, as shown in figure 1, where three on each side make their appearance at the same stage of growth. This number is subsequently increased to six or eight on each side in mature forms, sometimes becoming greater in old age. _ Internal Apparatus. The brachial supports in this species consist of spirals, coiled in the transverse axis of the shell, with their bases facing each other. In the mature individual, the number of coils is from eight to ten. The spirals are connected by an angular loop, the branches of which take their origin on the dorsal limb of the basal coils, and are directed ven- trally and backward to beyond the axis of the interior cavity, forming at 60 MEMOIRS OF THE STATE MUSEUM their junction not a simple angle, but a miniature sadd/e, from the posterior extremity of which extends straight backward a little spiniform process. The number of coils in these spires varies with the age of the shell. In preparing a series to show the development of these structures, it appears that the shelly ribbons composing the spirals not only make fewer coils in early life, but that these are of exceeding tenuity in the primary stages of development. The accompanying figures show the extremes of develop- ment noticed in these respects, figures 1 and 2 representing the character of the supports in the mature condition, and figure 3, the spirals as developed in an individual having a length of 2.5 mm., where the ribbon makes but Fig. r. Fig. 2. Fig. 3. Fics. 1, 2, 3. DEVELOPMENT OF INTERNAL APPARATUS IN RETZIA EVAX. two revolutions. As far as can be ascertained, the /oof undergoes no essential modification in these early stages, though its precise character in the example from which this drawing has been made, was not determined, but has been drawn in. The same arrangement, however, has been seen in an individual of but slightly larger growth. The growth of these spirals consists, primarily, in the addition to the number of coils, and, secondarily, in the thickening of the ribbon. In the first case, the increase in number must take place by addition to the apices of the coils, and, therefore, the embryonic or primary coils of the ribbon must be wholly concealed by later depositions upon them, both in length and width. The apparent looseness of the coils in their primary condition SILURIAN BRACHIOPODA 61 must, however, be regarded as largely due to magnification, the distance between successive coils being actually not so great as the distance between the apical turns of the ribbon in the mature spiral. RETZIA SOBRINA, Sp. Nov. PLATE V, Fics. 10-16 Rhynchonella whitit, Hall, zn part. In the examination of alarge number of the specimens which have usu- ally passed under the name of Rhynchonella whit, we have become con- vinced, that, aside from the individuals which agree with the types and the description of the species, there is a series of shells, which, in the mature state, may be readily confounded with immature stages of R. whz¢z7, but in their immature condition are readily separable from this species, and form, of themselves, a satisfactory and well-defined developmental series. The simi- larity of these examples with RX. whz¢cz is found in the general outline, the strong, simple plications approximately the same in number, and the usual two plications on the median fold. The external differences, however, ‘in the new species, are these: the plications on the fold may be one or three, and whatever their number, the fold is always depressed, in most instances even to obsolescence, and the plications upon it are low and often faint. The foramen, also, is circular in maturity, with perfectly developed deltidial plates, and the surface of the valves usually conspicuously marked by fine, crowded, concentric growth-lines. Internally, the difference is more emphatic, as carefully prepared specimens show well-defined spirals having their apices near the lateral margins, as shown on plate 5, figure 12. While disavowing the intention of describing new species as remote from the purposes of this paper, we have, for convenience’s sake in utilizing this form for our work, to which it makes no unimportant contribution, desig- nated it as above, as no doubt exists of its specific value. Retzia sobrina, one of the more abundant of the Waldron brachiopoda, is itself subject to some variation, more considerable indeed, than that no- 62 MEMOIRS OF THE STATE MUSEUM ticed in either of the species Rhynchonella whittt and R. neglecta. Our material represents all developmental stages between the limits of these dimensions; 2x1.6 mm. (incipient shell) and 7x6.5 mm. (maturity), In its youngest stages, it shows a certain degree of similarity with Retzza evax, especially in the sinus on both valves, and in the sinal plications, The greater number of the latter in 2. evax, as well as the more numerous lateral plications, will serve to obviate confusion here. SPECIFIC CHARACTERS Mature Form (plate 5, figs. 11, 11a, 116). Shell small, rotund, in outline broadly ovate to subpentagonal. Valves of equal convexity. Ventral valve with umbo prominent, attenuate, erect, and slightly in- curved at the apex; cardinal margins not excavate, sloping with a faint curve to the sides, whence they round to the anterior edge, which, in the sinal region, is nearly straight; cardinal area distinct ; foramen circular ; deltidial plates prominent. Dorsal valve subcircular in outline, arched in the umbonal region ; beak well-defined, apex concealed. In the umbonal region, the median portions of both valves are slightly more convex than elsewhere, but this prominence disappears toward the margins, the valves becoming slightly flattened and depressed on the median region near the anterior margin, making a low sinus on the ventral, and a low, depressed fold on the dorsal valve. Both fold and sinus may bear one, two, or three small, often faint and unsymmetrically developed plications, the strongest of which may have its origin in the umbonal region, while the others rarely extend more than half-way across the shell. On each of the latera are four or five strong, angular, simple plications, making thus from nine to thirteen plications on each valve. The increase in these takes place altogether on the fold and sinus, the full quota of lateral plications appearing early in the history of the individual. The plications are covered by numerous fine, concentric growth-lines more noticeably developed near the margin, and at intervals becoming varicose. SILURIAN BRACHIOPODA 63 The spiral brachial supports each make about five revolutions, which come to an apex near the lateral margins. Variations from the normal mature form. An elongate form with an unusually high and straight beak is not of rare occurrence, and is the result- ant of a very completely represented series of embryonic stages. The spe- cies is also subject to odese growth, resulting from two sources ; (a) general internal thickening of the shell, (4) marginal thickening. Both are the result of post-adolescent or senile growth, the former producing a round, full, plethoric shell, the latter giving the shell a truncate appearance. Incipient Form (plate 5, figs. 10, 102). The first stage of growth represented in our series measures 2 mm. in length by 1.6 mm. in width. The valves are subequally convex, somewhat depressed anteriorly. Outline broadly ovate. Ventral valve with beak high, erect, and subacute; cardinal slopes broad, steep, and slightly excavate ; pedicle-aperture subtriangular, rounded at the apical angle, and also slightly, at the base, by the already developed deltidial plates. . Dorsal valve subcircular, beak full, rounded, sides slightly appressed, apex concealed. Surface of the dorsal valve marked by two thread-like pli- cations which take their origin medially, just below the umbonal region; thenceforward they rapidly diverge, forming the embryonal sinus, which is, however, soon filled by two small plications. The latera each bear one plication, of earlier age than the sinal, and later than the primary plica- tions. On the ventral valve, the plications number the same, but the embryonal fold or dorsum is more strongly marked than the dorsal sinus. On both valves, indications of the mature fold and sinus begin with the appearance of the sinal plications. DEVELOPMENTAL VARIATIONS General Form and Outline. There is'a gradual increase in convexity and diameter with each successive growth-stage, until maturity is reached. 64 MEMOIRS OF THE STATE MUSEUM The elongate variation from the normal seems to have retained through all stages of growth the proportions of the normal embryo. Beak and Foramen The erect, straight, subacute beak of the incip- ient shell, in later growth becomes rounded and slightly arched or incurved. The cardinal area in all stages of development is, however, high, exceptions being made for the more extreme cases of obesity, where the deltidial plates may be concealed, but the foramen is always exposed, and the beak is never procumbent on the opposite umbo. The plates arising from the base of the thickened foraminal margins, meet in such a manner as to leave the foramen sharply acute below, and subtriangular. By their subsequent upward growth and more complete union, the foramen becomes circular, the lines of symphysis with the valves still remaining thickened. In occasional instances, a probable slight displacement of the plates outwardly along the median suture, gives them the appearance of sloping away from the median to the lateral sutures. Ca@LOsPIRA DISPARILIS, Hall, 1852 Pate V, Fics. 17-23 —— — , Hall. Twenty-eighth Ann. Rept. N. Y. State Mus. Nat. Hist., p. 162, pl. 25, figs. 39-43. — eee Eleventh Ann. Rept. State Geol. Indiana, p. 303, pl. 25, figs. 39-43. 1882. Although this species is one of the less abundant members of the Waldron fauna, we have found several hundred immature individuals, the youngest of which has dimensions of 2.5 mm. length by 2 mm. width, the greatest size at maturity being 6.5 mm. length by 6 mm. width. The species being, in its mature size, quite small, and, in its surface features, quite simple, it does not afford such scope for variations through the later embry- onic stages as many of its associated species and hence, it will be noticed, that in surface sculpture, a permanency of character is retained through all stages of growth. 7 SILURIAN BRACHIOPODA 65 SPECIFIC CHARACTERS Mature Form (plate 5, figs.19, 19@,194). . Shell small, suboval or cordate, often subpentagonal ; plano-convex, greatest’width along the hinge. Ventral valve convex, depressed at the sides ;,beak exsert, and in old forms arcuate. Dorsal valve flat and sometimes depressed near the beak. The ventral valve is marked by two very prominent plications which pass along the deep median sinus, and are accompanied by two less distinct pli- cations on each of the latera, making in all six plications, of which the two nearest the hinge-line are sometimes obsolescent. The dorsal valve bears a prominent median fold, and two well-marked plications on the lat- eral portions of the shell. Toward the margin are concentric lamine of growth. An average adult individual measures 5.5 mm. in length by 5 mm. in width. Variations in Outline. The individuals divide themselves into two groups according to their outline : (a) normal form. (4) long form. The first of these groups includes the great majority of all individuals found, which are characterized by a relatively broad figure and subcircular out- line. Members of the second group are comparatively few in number, and - are elongate or subovate individuals. The long form (é) is well defined in immature growth-stages, and appears to be a permanent varietal difference. Abnormalities. A variation in adult shells, noticed only in rare instances, is a tendency to an asymmetrical development in the plications, as shown on plate 5, figure 18, where, by unequal growth upon the lateral por- tions of the shell, the median plication on the dorsal vaive is deflected to one side, and the corresponding median sinus on the ventral valve displaced, the axial line of the shell being occupied by one of the strong plications bounding the sinus. Another form of this asymmetry is manifested in the ; 66 MEMOIRS OF THE STATE MUSEUM intercalary addition of a single plication on one side of the median plica- tion of the dorsal valve. A tendency to obesity is often manifested by the shell, at or before reaching the average dimensions of maturity, when it may be supposed that the full growth of the individual has been attained. This obesity is produced by a rapid thickening of the shell at the margins, making the anterior face truncate and forcing the ventral beak over the dorsal in the same manner as if the valves were forced to open along the hinge. It is, therefore, only in individuals which have reached this obese condition that the ventral beak is incurved. DEVELOPMENTAL CHANGES The character of the primal or elemental shell may be seen from a single example (plate 5, fig. 18), in which the plications are abruptly developed at a distance of 1.5 mm. from the apex, and, presumably, that portion of the shell within this limit, represents approximately the size of the original embryonic shell. This portion of the individual is quite smooth, and shows but a trace of the median fold and sinus. As already observed, there is a marked permanency in the surface features of the species from early youth to maturity. The smallest individual obtainable bears, as in the mature condition, six plications on the ventral and five on the dorsal valve, though those near the hinge-line are quite faint. The éeak is prominent and exsert, except in obese shells, where it is incurved. In the earliest stage where the character of the foramen is well preserved the individual has a length of 4 mm. and a width of 3.5 mm. Here it is seen to be elongate-oval, the deltidial plates having formed to such a degree as to be in contact with each other and to have anchylosed, so that the median suture is detected with difficulty. The lateral sutures | always remain distinct even to maturity, and it is evident that the union of the plates with the shell along these joints has not been as firm as in many species, as it is not infrequently found that the plates have been displaced ‘ SILURIAN BRACHIOPODA . 67 and lost. Careful search among the smallest individuals has shown no trace of the inceptive triangular outline of the pedicle-groove existing in other species before the formation of the deltidial plates. It is an important fact that the foramen begins to assume its mature condition so early in the history of the shell, although its development was evidently in conformity with the general type. The subsequent development of the deltidial plates changes the form of the foramen to that of a circle, as shown in figures 22 and 23. Inthe early life of the shell, the plane of the foramen is in, or parallel to, the axial plane; at maturity, before any obesity or senile thickening takes place, the foramen, in becoming less elongate, truncates the apex of the valve, and makes a large angle (sometimes almost 90°) with the axial plane ; subsequently, with increase in obesity, it becomes again more nearly parallel to this plane. In the last condition, the deltidial plates are curved inwards, and often to a large degree concealed. MERISTELLA RECTIROSTRA, Hall, 1882 PLATE VII, Fics. 4, 5, 11-13 — —, Hall. Eleventh Ann. Rept. State Geol. Indiana, p. 301, pl. 27, figs. 10-14. 1882. This small species is one of the less abundant of the brachiopods of this fauna, and probably has often been confounded with undeveloped indi- viduals of Merdstina nitida. It presents, however, adult features which will not allow it to be confounded with that species, and although some. diffi- culty arises in separating the diminutive forms of the two species, IZ. rect?- rostra is characterized by the absence of deltidial plates in every stage of its existence. ? The series representing this species does not include stages of growth as early as in some of the others, but is sufficiently complete to permit the statement that, were younger forms accessible, they would probably add little to our knowledge of the developmental changes. The series begins 68 MEMOIRS OF THE STATE MUSEUM with individuals having a length of 2.5 mm. and a width of 1.75 mm., the adult form measuring 9 mm. in length by 7.5 in width. In all stages of growth earlier than that approximately indicated by a size of 6x4 mm., it is very difficult, and from our observations impossible, to draw the line of separation between this species and JZ. xztéda, and the fact which has been demonstrated for Orthzs elegantula and O. hybrida, viz.; that in the earliest growth-stages no specific differences are .manifest, will probably be found to hold good for these two species also.* And in the latter case a considerably larger size is attained by the embryo forms than is reached by the former species, before the differential characters are assumed, This is due to the fact, that these two species, when mature, have essentially no surface sculpture, and differ less in general form and outline than do the mature individuals of Orthes. SPECIFIC CHARACTERS Mature Form (plate 7, figs. 12, 12a, 126). Shell subpentagonal or ovate ; beak erect, acute, and prominent, rapidly widening toward the base. Lateral margins nearly straight for about one-third the length of the shell, thence rounding to the anterior margin. Valves about equally convex, giving the shell a sublenticular contour. Ventral valve with attenuate, straight, or slightly arcuate beak. Fora- men triangular and without deltidial plates. Dorsal valve more nearly subpentagonal in outline ; beak incurved into the foramen of the ventral valve. Surface smooth, or in rare instances. showing a faint pseudo-punctate appearance which is entirely superficial. Dimensions of average adult 97.5 mm. *In accordance with the intention already expressed, not to enter into discussions of synomymy and generic values, we have followed Mr. Hall in referring these species (7. rectz- rostra and M. nitida) to different genera. We believe, however, that the character of the loop will prove them to be congeneric. SILURIAN BRACHIOPODA | 69 Incipient Form (plate 7, figs. 4, 4). Shell measuring 2.5x1.75 mm. Oval, proportionally longer and narrower than in the adult state. Beak elevated, acute, straight. Foramen of the ventral valve very broad, triangular, extending to the apex. Dorsal beak full, rounded and incon- spicuous. Shell convex just below the beak, becoming depressed toward the anterior margin. DEVELOPMENTAL VARIATIONS General Form and Outline. In the incipient stadia of growth, the shell is extremely elongate and quite perfectly oval ; the beak of the ventral valve is relatively broad, its lateral margins having a slight outward curve. | With growth, the shell broadens, and the ventral beak becomes more atten- uate while the greatest width of the shell, instead of being at or below the middle, comes nearer the hinge-line. Beak. From being erect, straight, and relatively broad in the ventral valve, at the outset, it becomes, at maturity, narrow, attenuate, and slightly incurved toward the apex. Foramen. In the earliest observed stage, the foramen is a broad, triangular opening, covering nearly the entire cardinal area, reaching, but not encroaching upon the apex of the valve. In subsequent stages of development, this opening narrows with the narrowing of the beak, but, as at no stage deltidial plates are developed, the contraction is due to the en- croachment of the cardinal portions of the valve along the foraminal mar- gins. The interesting fact of the persistent absence of deltidial plates throughout the entire existence of the individual, may be interpreted as a retention to maturity, of a character embryonic in allied species; the small size of the mature shell and the very slight incurvature of the ventral beak also contribute to the embryonic expression of the species. 70 MEMOIRS OF THE STATE MUSEUM Meristina NitTrpA, Hall, 1843 PLATE VII, Fics. 6-10 —— —-, Hall. Twenty-eighth Ann. Rept. State Mus. Nat. Hist., p. 160, pl. 25, figs. 1-7. 1879. —— —, Hall. Eleventh Ann, Rept. State Geol. Indiana, p. 300, pl. 25, figs. 1-7. 1882. Meristina nitida is a very abundant and characteristic fossil in the Niagara fauna of central Indiana, reaching a much greater development both in size and numbers than in the New York outcrops of the formation. The individuals vary in size from a length of 2.5 mm. and a width of 1.75 mm., to a length of 25 mm. and a width of 22 mm., and the series represent- ing these variations is, on account of the abundance of specimens, very complete within these limits. It is, however, a noticeable feature of the species that in most respects, except size, the characters of maturity are assumed early in the life of the individual, and as the form is essentially devoid of surface sculpture, the interest in its development rests to a larger degree than usual upon abnormalities in individuals either mature, or ap- proaching maturity. SPECIFIC CHARACTERS Mature Form (plate 7, figs. 9, 9a, 90). Shell broadly subpentagonal to ovoid; beaks extended and more or less prominent. Ventral valve with the greatest convexity at about one-third the length of the shell in front of the beak. Beak arched, incurved over the dorsal valve ; apex evenly truncated, the circular foramen lying in a vertical plane. Cardinal slopes extending for more than one-half the length of the shell. A low median depression is noticeable on the younger portions of the valve. Dorsal valve with a similar convexity ; beak incurved and concealed. A very low and inconspicuous median elevation corresponds with the depression on the opposite valve. Surface smooth or with fine concentric strize and a few conspicuous lines of growth toward the anterior margin. Average individuals measure 20x 16 mm., large examples not infrequently 25x21 mm, ‘ SILURIAN BRACHIOPODA 71 Variations in Outline. Two very distinct groups of forms are evi- dent in this species, in one of which, (@) xormad/, the outline of the mature shell is obcordate or subpentagonal. When immature, the anterior margin is evenly circular, but in all cases the proportion of length to width is essen- tially the same. Probably five-eighths of the specimens found belong to this group. In a second group, (4) dong form, the shell is elongate-spatulate, and proportionately deeper than the normal, but, with a single exception, indi- viduals have not been observed to exceed a length of 10 mm. and a width of 7mm. This variation is so persistent that it appears to be well founded genetically, and not merely an occasional occurrence. Tracing backward from the mature shell to the earlier stages of development, we find both this and the normal form merging into each other, hence both have had a similar starting point. The long form, however, reaches maturity of development at a very early age, and never approaches the size or propor- tions of the normal adult. A tendency to odeszty is especially noticeable in the group (4), the majority of such individuals being below the normal full growth. A single adult example shows traces of broad, rounded plications on each side of the fold and sinus, a singular condition in a species uni- formly non-plicate. Incipient Form (plate 7, figs. 4, 4a, 10, 102). Shell 2.5 mm. in length by 1.75 mm. in width ; elongate, oval ; beak elevated, straight, acute. Pedicle-aperture of the ventral valve very broad, triangular, extending to, but ‘not encroaching upon the apex. Dorsal beak full, rounded, but incon- spicuous. Valves convex just below the beaks, becoming depressed toward the anterior margin. The shell is proportionally much narrower than the adult form. The starting point of our series is precisely the same form of shell as that taken for the incipient stage in the species Merdstella rectirostra. 72 MEMOIRS OF THE STATE MUSEUM Under the discussion of that species, reference has been made to the impos- sibility of separating these two species, in their earlier stages, and we are left to regard the impression of the specific characters as .of subsequent development. DEVELOPMENTAL VARIATIONS The surface characters being unvariable, the important changes in development are confined, as far as observable, to the pedicle-aperture and deltidial plates. As already observed, the beak is incurved so early in the history of the individual that these embryological changes can be observed only in very young specimens. This incurvature of the ventral beak appears to become fixed earlier in the normal than in the elongate form, For example, figure 10, plate 7, represents an elongate individual with a length of 2.5 mm. and a width of 1.5 mm., with an open triangular foramen, and no apparent development of the deltidial plates, but the normal form of the same size has the plates developed, the foramen nearly circular and the beak incurved. In the condition represented in this figure, the embryos of this species are readily confounded with Jerdstella rectzrostra, in which the triangular aperture is retained until maturity. The latter species is, how- ever, distinguishable in all the later stages of its existence by the body of the shell being broader and the ventral beak narrower and more attenuate. Individuals which show the deltidium in its different phases are diff- cult to obtain on account of the tendency of the beak to incurvature as soon as the plates begin to form. An individual is represented in figure 7, plate 7, of somewhat abnormal height of beak, showing an intermediate stage of growth in the plates and the formation of the foramen; and in figure 8, an individual of the same size with the foramen circular, and the deltidium completed and concealed by the infolding of the beak. SILURIAN BRACHIOPODA 73 WHITFIELDIA MARIA, Hall, 1863 Prate VII, Fics. 1-3 Mertstella Maria, Hall. Trans. Albany Inst. vol. iv, p. 212. 1863. Meristina Maria, Hall. Twenty-eighth Ann. Rept. N. Y. State Mus. Nat. Hist., p. 159, pl. 25, figs. 8-12. 1879. —— —,, Hall. Eleventh Ann. Rept. State Geol. Indiana, p. 299, pl. 25, figs. 8-12. 1882. * Whitfieldia tumida (Dalman Sp.), Davidson. Supp. Brit. Sil. Brach., p. fo7. 1882. This species may be regarded as presenting a general external form and effect diametrically opposed to that in Werzstella rectirostra. To the erect, attenuate, acute beak, open pedicle-aperture, shallow valves, and asinuate anterior margin of the latter, the full, rounded, incurved beak, concealed cardinal area, ventricose valves, and strongly sinuate anterior margin of W. marta are strongly contrasted. Between the mature characters of these two species, Weristzna nitida is conspicuously mediate. Immature specimens of W. marza are far from abundant. Indeed, our series shows only about thirteen different grades of development, and the smallest individual which can be referred with certainty to the species measures 6x6 mm. (adult 29 mm. in length by 32 mm. in width), We have, however, assigned to the species a minute embryo measuring -75x.75 mm., and if this is correctly done, the embryos of this species in the earliest stages of growth differ from those of the other non-plicate species here discussed in a much stronger tendency toward a circular outline. The beak of the ventral valve becomes incurved, and the cardinal area obscured very early, so that the discussion of the development of these parts is necessarily much curtailed. * The late Mr. Davidson identified the Waldron species with the Atryfa ¢umida of Dalman, — the type of his genus Whitfieldia. We use the term WAztfieldéa here for convenience, but if the identity of the American and European forms is established, 4¢ryfa tumzda will have been taken as the type of two (Meréstina, Hall, Whitfieldia, Davidson), if not of three (dJeréstel/a, Hall) genera. 10 74 MEMOIRS OF THE STATE MUSEUM SPECIFIC CHARACTERS Mature Form (plate 7, figs. 3, 3a). Shell comparatively large, ven- tricose, broadly ovate or subpentagonal. ; Ventral valve gibbous in the umbonal region, with a low, broad dorsum extending from the umbo to near the middle of the valve, where it becomes flattened, sinuate, and at the anterior margin is reflected dorsally into a linguiform extension. Beak closely incurved over the dorsal valve, fully concealing the foramen. Cardinal slopes angulate, and slightly excavate. Dorsal valve evenly convex, somewhat gibbous, strongly arcuate trans- versely along the dorsum, which becomes elevated into a low fold, deeply emarginate in front for the reception of the extension from the opposite valve. Beak obtuse, incurved and concealed. Surface smooth, marked by concentric growth-lines near the margin. Occasionally, individuals of large growth show a greater length than breadth, presenting an elongate form, but this variation seems to be due to more rapid axial growth after the attainment of adult size, and does not manifest itself in the incompletely developed shells. Incipient Form (plate 7, figs. 1, 1a, 2, 2a). The minute shell which appears to have been the initial form for the species, has a circular outline and depressed convex valves. The ventral valve is evenly convex, with the beak erect, short, and broad. The cardinal area is low, the foraminal aperture triangular, reaching to, but not encroaching upon the beak. The deltidial plates are absent. Dorsal valve with the beak not incurved but inconspicuous. Neither valve bears any trace of. a median elevation or depression. DEVELOPMENTAL VARIATIONS General Form and Outline. An inclination toward a lenticular form and circular outline is noticeable in all immature individuals. Until a size of about 18x18 mm. is attained, there is rarely, if ever, any trace of the strong marginal fold of maturity. SILURIAN BRACHIOPODA | 75 Beak. The low but erect ventral beak of the initial shell, has, in the next stage of growth, become inflected and obtuse, not, however, so as to conceal the foramen, which remains apparent above the apex of the dorsal valve, until the rapid increase in convexity, which immediately precedes maturity, sets in. Thereafter, the ventral beak becomes more closely in- curved, and thrust over upon the dorsal valve, to the loss of all external trace of the cardinal area. Foramen. The elemental hiatus is shown in the initial shell and the subsequently developed deltidial plates in the next growth-stage. In the latter case, the foramen has become nearly if not quite enclosed and has also encroached upon the apical portion of the valve, which forms about one-half its periphery. In all subsequent stages of growth, the deltidial plates are concealed, and whatever portion of the foramen appears there- after above the dorsal valve is enclosed by the circumbonal tract. With the approach of maturity, this gradually disappears, and at full growth, every trace of it has become obliterated. SPIRIFER Crispus, Hisinger, 1826 Puate VI, Fics. 6, 7 SPIRIFER CRISPUS, var. SIMPLEX, Hall, 1879 Pate VI, Fics. 4, 5 SPIRIFER BICOSTATUS, Vanuxem, 1842, var. PETILUS, Hall, 1879 Puiate VI, Fics. 1-3 Spirifera crispa, Hall. Twenty-eighth Ann. Rept. N. Y. State Mus. Nat. Hist., p. 157, pl. 24, figs. 6-12, 19. 1879. | — ——, Hall. Eleventh Ann. Rept. State Geol. Indiana, p. 295, pl. 24, figs. 6-12, 19. 1882. Spirifera crispa, var. simplex, Hall. Twenty-eighth Ann. Rept. N. Y. State Mus. Nat. Hist., p. 157, pl. 24, figs. 1-5. 1879. ) — —- —,, Hall. Eleventh Ann. Rept. State Geol. Indiana, p. 286, pl. 24, figs. 1-5. 1882. Spirifera bicostata? var. petila, Hall. Trans. Alb. Inst., vol. x, Abstract, p. 15. 1879. — — —, Hall. Eleventh Ann. Rept. State Geol. Indiana, p. 297, pl. 27, figs. 8, 9. 1882. The three forms which are here treated together, are closely allied in all their general characters. It is in their initial stages, however, that the 76 MEMOIRS OF THE STATE MUSEUM resemblance becomes more than superficial, for, in young shells of less than 2mm. in length, it is difficult, and sometimes impossiblé, to refer them to any one of the three groups. A general expression of the common charac- ters is furnished by the young of \S. crzspus, var. stmplex, illustrated by figure 4, on plate 6. Taking S. dzcostatus, var. petilus as the simplest form, the young shell - is found to be nearly circular in outline, with a single, broad, median fold _on the dorsal valve. Passing to .S. cr¢spus, var. simplex, of the same size, the outline is seen to be broader, and there is an incipient plication on each side of the median fold. The outline is still broader in S. crzspus, becoming decidedly subelliptical, and the two lateral plications on the dorsal valve are nearly equal in strength to the median fold. The surface ornamentation consists of fine spinulose, or granulose, concentric striz, differing very little in any of the three species. In tracing the development of .S. dzcos¢atus, var. petzlus, the shell is found to retain its embryonic characters up to full growth, neither materially changing its form, nor adding to the primitive number of plications. Likewise, .S. crzspus var. semplex changes very little except to increase in width and add a pair of plications at maturity. Individuals of S. erzspus develop parallel to the variety szmflex, up to a length of 5 mm.,, or until about two-thirds the size of full-grown examples is attained. Subsequently, more plications are added, increasing the number from three or five to eleven, but otherwise, the general features of the shell are unchanged. Even the relative convexity of the valves remains the same at all periods, In the incipient forms, the cardinal line extends for about one-fourth the width of the shell, and at maturity measures three-fourths of this width, The foramen does not develop at the same rate; at first, it occupies one- half or one-third of the ventral area, but advancing growth gradually diminishes this ratio, until it is one-fourth or one-fifth the size of the hinge- area. Two narrow, triangular, deltidial plates are present in full-grown SILURIAN BRACHIOPODA 77 individuals, but they do not serve to close the fissure which remains open in all stages of growth. S. crispus, var. simplex reaches a width of 8 mm., and |S. crzspus often measures 22 mm. in width. Occasionally, a specimen of S. crzspus of the usual size is found with but seven plications on the dorsal valve, suggesting: a very large example of the variety, or that the characters of the smaller and simple form are sometimes continued far beyond the period when they usually disappear. Also, the features both of the species and variety may be combined in a single specimen, as one abnormal example has three pli- cations on one side of the median fold and four on the other. SPIRIFER RADIATUS, Sowerby, 1825 Piate VI, Fics. 9-11 Spirifera radiata, Hall. Twenty-eighth Ann. Rept. N. Y. State Mus. Nat. Hist., p. 157, pl. 24, figs. 20-30. 1879. - — — Hall. Eleventh Ann. Rept. State Geol. Indiana, p. 296, pl. 24, figs. 20-30. 1882. The series of specimens representing the gradation in size from very young to mature forms is quite complete, but, unfortunately, the characters of the most interesting feature, the deltidium, are not well shown. The foramen is usually but partially closed when the shell reaches nearly its full dimensions, and at this period, the beak of the ventral valve is so incurved and thickened that the detailed development of the deltidial plates is obscured, and rendered difficult of interpretation. This species has been so fully discussed in all its aspects, on account of its wide geographical distribution and varied physical conditions, that a diagnosis of the adult form is unnecessary in this place (vzde plate 6, figs. Il, 11@). Incipient Form (plate 6, figs. 10, 102). The smallest example yet detected has a length of 1.5 mm. The specimen is not well preserved, and the one used for illustration and description is somewhat larger, measuring 78 MEMOIRS OF THE STATE MUSEUM 2mm. in length. The differences appear to be so slight that the characters of the larger may well be applied to the smaller individual. The shell is nearly circular, flattened, and with the beaks not incurved, but directed outward. The area of the ventral valve is broad, triangular, open, and extends nearly the entire length of the cardinal line. The incip- ient dorsal fold and ventral sinus extend nearly to the beaks, and on each _ side there are about ten radiating stria. Radii are also present on the fold and in the sinus. DEVELOPMENTAL CHANGES The changes in the shell from advancing growth are principally the gradual widening of the valves, on account of the extension of the cardinal line and extremities, and the incurving of the beaks, from the progressive increase in the depth of the valves. From being circular in outline, the shell slowly widens until it is one-seventh wider than long. The ventral beak in old specimens is so arched over the area as to nearly conceal it, and prevent the opening of the valves to any extent. In the early stages, the depth of the conjoined valves is about half the length of the shell, while in obese mature forms, the depth is equal to the length. The deltidial plates first appear as narrow elevated laminz along the sides of the fissure under the ventral beak. A specimen about half-grown shows them as represented in plate 6, figure 9, consisting of triangular plates approximately as in figure 3’, of the following diagram. They are subsequently united along their inner margins, and rarely, in the material at hand, can any appearance of a foramen be discovered. In old shells, the growth and thickening of the deltidium makes it rugose, and it nearly closes the area. From an examination of a number of species of Sfzrzfer showing considerable variety in the mode of development of the deltidium, we believe that there is no esssential difference, and that all intermediate con- ditions occur in this group, between the features represented in Spzrzfer7na SILURIAN BRACHIOPODA 79 by Deslongchamps (see Summary), and the characteristic mode of develop- ment in Zerebratula and Rhynchonella. The genus Sfircfer presents all these stages. In some species, the area is apparently closed by growth from the apex, and in others by the meeting of the deltidial plates at the base of the area and inclosing a foramen as in Rhynchonella. Spirifer niagarensts, S. perlamellosus, and S. cumberlandi@ are examples of the former mode, and .S. s#/catus and approximately S. radzatus represent the latter. Both conditions are reached by accretion along the inner edges of the del- tidial plates. The initial state is represented by a narrow elongate lamina on each side of the triangular area. Further growth produces a triangular plate, and to the form of the triangle is due the apparent growth of the deltidium from the apex of the fissure downwards, or from the base of the fissure towards the beak of the ventral valve. The accompanying diagrammatic outlines serve to illustrate the changes and the final results. Fic. 4. DetripiIAL DEVELOPMENT IN SPIRIFER. Figure 1 represents an area in an early stage of growth, with a narrow deltidial plate on each side, alike for each series. Figure 2 shows scalene triangular plates, with the shortest side at the base of the area. ‘ Figure 2’ shows plates with the two free edges more nearly equal. 80 MEMOIRS OF THE STATE MUSEUM Figure 2” presents narrow triangular plates as in figure 2, but with the shortest edges in the apex of the area. In figures 3, 3, 3’, the growth has continued in the direction initiated in the preceding stage, and the. apex of the area has been partially filled from the internal thickening of the beak. Figures 4, 4’, 4 show the completed deltidium with the circular perfo- ration. The plates in figure 4 nearly close the area, while in figure 4” the opening is nearly as high as wide. Further growth can now take place only along the lower free edges of the plates. Figure 5 represents the results of subsequent growth and thickening, which have obliterated the evidences as to the mode of development, and unified all three cases. The position of the foramen below the apex of the area does not appear to be due to the approximation and union of the deltidial plates, but to the lowering of the actual cavity of the beak. from the natural thickening of the shell, so that the foramen, as in other genera, is at the real termination of the ventral umbonal cavity. It is seen that the manner of development is alike in each case, varying only from differences in the form of the plates in the earlier stages. The finished deltidium is also the same, although the methods of attaining the result differ in each. Figures 1, 2, 3, 4 are represented by »S. sadcatus,* and vary in no im- portant particulars from the mode of development in 7Zerebratuda and. Rhynchonella. Figures 1, 2’, 3’, 4’ are partially represented by S. radzatus, although, in this species, the circular foramen is usually obliterated by subsequent thick- ening and growth, (Sze figures 10, 9, 11, plate 6.) Figures 1, 2”, 3” are well shown in S. xzagarensis (figure 8, plate 6), and the subsequent stages appear in mature forms of |S. ey teelloses: cand .S. cum- * State of New York, Report of hie: State Geologist ox: the reat 1882, published 1883, wih ad figs. 1, 2, 3. SILURIAN BRACHIOPODA 81 berlandie. Other forms, notably those with elevated areas, such as .S. macro- notus, S. medialis, together with Cyrtzna and Cyrtia, present considerable differences in the completed deltidium, due principally, it is believed, to the internal thickening of the beak and the growth of the transverse septum. The deltidium of Sfzrzfer thus appears to be the exact homologue of the same part in 7erebratula, Rhynchonella, etc., and to be radically differ- ent from the so-called “ pseudo-deltidium” of Strophomena, Strophodonta, Streptorhynchus, and allied genera, although this term has been currently applied to both the Spiriferidae and the Strophomenide. it SUMMARY OF DEVELOPMENTAL CHANGES Siz—E AND CONTOUR. Although the species described in the pre- ceding pages present a wide variation in form and general appearance, the nature of the changes which take place in the development of the shell is remarkable in its uniformity. In nearly every species, the inceptive state is represented by a shell having a subcircular outline, with valves of slight convexity. This phase usually disappears before the individual reaches a length of 1 mm., after which the specific characters are assumed, and are progressively emphasized with each succeeding increment. On comparing the incipient stage in these fossil shells with that of recent brachiopods, as given by Mr. E. S. Morse for Zerebratulina, and by Mr. W. K. Brooxs for G/o¢¢dédia, we find that, in respect to actual size, there is a slight, though perhaps unessential difference. At the earliest stage of growth figured by Morsz,* the shell has a length of about .3 mm. and in the next stage represented, of approximately .6 mm. *Memoirs of the Boston Society of Natural History, Vol. ii; On the Early Stages of Terebratulina septentrionalis, pl. I, figs. 2, 3. 1869. 84 MEMOIRS OF THE STATE MUSEUM The first two stages of the shell figured by Mr. Brooxs* represent free animals, and measure .24 and .3 mm. in length, respectively. The shell became attached by the pedicle only upon attaining a length of 2.5 mm. Most of the fossil forms have furnished evidence, either from actual elemental specimens or from the apical portions of subsequent _incipient stages, that the true initial shell did not reach a size of more than.5 mm. in length. Soon after this period, the characters of each species become developed and impressed upon the shell more or less gradually. Even such distinct groups as Ahyuchonella, Spirifer, Athyris, Rhynchotreta, Anastrophia, Nucleospira, and the Meristoids, in their initial stages, approach one another so closely that they can be determined only from comparatively trivial features. They are alike in form, con- tour, convexity, beaks, and cardinal area, and the only marked differences are to be found in the faint indications of plications, striz, folds, and sinuses. For species of some genera, as Orthzs, Whitfieldia, and Spirzfer, even these characters are not determinative, and it is impossible to refer certain embryos to their proper place. From the foregoing statements, it would naturally be inferred, that the species which, at maturity, present characters abnormal to the typical structure, have been diverted from the harmony which existed in the incipient stages, with the other members of the group. This has been shown to be the case in all the reversed species above examined, belong: ing to the genera Anastrophia, Strophonella, and Streptis. Beginning with the initial shell having a circular outline and de- pressed valves, we find that subsequent growth takes place about the periphery, andein the majority of species, the convexity is gradually increased until maturity is. reached. This assertion does not hold true *Johns Hopkins University; Chesapeake Zodlogical Laboratory. The Development of Lingula and the Systematic Position of the Brachiopoda, plates 1 and 2. 1879. SILURIAN BRACHIOPODA 85 for such forms as the Strophomenide, which vary in convexity, either very slowly or not at all, up to individuals about half-grown, when the valves become more or less deflected and often concave. Such a re- version in the shell is in conformity with the degeneracy which is traced in the development of the cardinal area-and pedicle-sheath, mentioned on a subsequent page. The observations of Brooks and Morss, in the works just cited, show, that in both the hingeless and the hinged brachiopods, as repre- sented by Lingula and Terebratulina, the early stages of the shell approach a subcircular outline, and Brooxs remarks (of. c7¢. p. 43), that “the recent and fossil shells of the various species of Crania, Lingula, Lingulella and Obolus, and other hingeless Brachiopods,’ furnish a series of adult forms representing all the changes through which the outline of Lingula pyramidata passes during its development.” In these respects, then, uniformity is established in the embryology of the ancient Silurian types and their modern descendants. VALVES. The dorsal valve in young shells is smaller than the opposite, and usually more depressed. These relations, as a rule, are continued up to adult size, except that the ventral valve often increases more rapidly in convexity, producing a consequent incurving of the beak over the cardinal area, as in Orthis and Rhynchonella indianensts. Some species present both beaks as incurved, a condition well represented in Whitfeldia maria, Eichwaldia reticulata, Rhynchonella acinus, and R. neglecta. \n Anastrophia, the comparative relations of the valves become reversed from their initial condition, on account of the more rapid in- crease in the depth of the dorsal valve, so that, at maturity, the dorsal beak is much incurved, and often the umbo extends beyond that of the other valve, although the beaks preserve their normal condition of superposition. Several of the species show an embryonal sinus in the dorsal valve, 86 MEMOIRS OF THE STATE MUSEUM with a corresponding fold in the ventral, beginning soon after the initial stage of the shell has been passed, and disappearing before the shell is half-grown. Those forms presenting this feature to a marked degree are Rhynchotreta cuneata, Rhynchonella whitit, R. indianensis, R. neglecta, R. actnus, Atrypa reticularis, and Retzia sobrina. In Rhynchotreta cuneata and Aétrypa reticularis (plate 4, figs. 12-15, and plate 6, figs. 12-14), we have shown the gradual inception of this sinus, its maximum develop- ment and obsolescence, and, finally, its reversion into a fold which there- after persists and usually increases in prominence in all the succeeding stages of growth. The embryonal sinus is not present in Sferdfer, Anastrophia, Echwaldia, Whitfeldia, Meristina, Orthis, nor in the Strophomenide. Such of these as show a dorsal fold or ventral sinus, have them developed early in the growth of the shell, and they usually increase regularly to the time when the full size of the shell is attained. Breaks. The beak of the ventral valve in its earliest condition is commonly erect, pointed outwards, and of a broad triangular form, while that of the dorsal valve is small, not prominent, and lies in the longitudinal axis of the shell. In all cases, the subsequent deepening of the valves tends to incurve the beaks toward the cardinal area. The degree of in- curvature varies greatly in the different species. MMerdstella rectirostra shows a minimum, and Whztfieldia maria or Atrypa reticularis,-a maxi- mum, and between these limits all intermediate conditions occur. The usual degree of incurvature is presented in Spzrdfer radiatus, Retzia evax, and the Rhynchonellide. The outlines on plate 4, illustrating the profiles of the beaks in a series of Rhynchotreta cuneata, represent an uncommon condition, for in this species, the ventral beak, from its divergent initial position, gradually approaches, and at maturity attains parallelism with the longitudinal axis of the shell. It never becomes sufficiently incurved to conceal, to the slightest degree, the deltidial area, while the initial dorsal beak becomes more ES SILURIAN BRACHIOPODA 87 and more incurved, until, finally, it lies entirely within the ventral umbonal cavity. Those species furnished with a circular apical perforation, as Atryfa reticularis, Retzia evax, and Rhynchotreta cuneata, lose the initial point of the ventral beak from absorption, due to the increase in the size of the per- foration or to its final terminal position. In Atrypa reticularis, or Whit- fieldia maria even both beak and perforation are destroyed, from the forcing of the ventral beak into contact with the dorsal umbo, produced by the great increase in the depth of the valves from growth along their anterior margins. CARDINAL AREA. Omitting for the present the Strophomenide and Orthidz, the initial state of the ventral cardinal area for all other forms is a broad triangular opening beneath the beak, with simple sharp margins. This condition is never passed by Merdstella rectzrostra, which shows a uniform, open, triangular area in every period of growth. A farther advanced state of progress initiates the deltidial plates, which first appear as narrow laminz along the sides of the area. The areal de- velopment of Spzrzfer crispus, Rhynchonella neglecta, and R. acinus, ceases at this point. In the next stadium, the further growth of -the deltidial plates along ~ their free edges gives them a triangular form, and they tend to narrow the limits of the opening and define the peduncular foramen. Spzrz/er nzagar- ensis and Rhynchonella whitit represent species which are arrested at this - period. The completed growth shows the deltidial plates uniting by symphysis along a median line, and inclosing near the apex of the area a more or less circular pedicle-perforation. Rhynchotreta cuneata, Whitfeldia maria, Retzia evax, etc., after passing through all the earlier conditions, reach this limit of development. The results of senile and extravagant growth often obliterate or de- 88 MEMOIRS OF THE STATE MUSEUM generate the normal deltidial advancement, the plates becoming thickened and their features obscured, while in some species processes are given off, as in a number of the Mesozoic Rhynchonellide. The cardinal area of the Strophomenidz in its early phase shows a small pedicle-sheath for the ventral valve and a narrow grooved process under the beak of the dorsal. The perforation for the passage of the ‘peduncle does not materially increase in size with the growth of the shell and often is obliterated, while the dorsal callosity usually reaches a consid- erable development. Additional evidence of the degeneracy of the pedicle is afforded by many species of other genera, which have a calcareous attachment to for- eign objects at the apex of the ventral valve, the pedicle, therefore, becom- ing functionally obsolete. Observations having some analogy with the facts here presented have been made, in a very restricted sense and usually incidentally, by various authors. Our own results, though derived from the species of a single fauna, must not be given too limited an application, for they involve nearly every important family of paleozoic articulate brachiopods, and we may tentatively assume that, as a rule, the essential features of variation ob- served in any member of a genus will hold good of the other members. In regard to the development of the characters of the pedicle-passage, ‘z. ¢. the deltidial plates and the foramen, there is good reason to regard the process as substantially identical in all the genera represented, making the necessary allowance for the peculiar variation seen in the Strophomenide, which may not, however, prove it an exception to the general statement. The various terms which have sometimes been applied to the condition of the deltidium in the rostrate genera, as de/tzdiwm amplectens, when the foramen is entirely surrounded by the plates, as in various Mesozoic Rhyn- chonelle (but in no paleozoic species of which we are aware), de/tzdium sec- tans, when the plates bound the foramen only on the lower side, the upper a ——— os gel, | eet em SILURIAN BRACHIOPODA | 89 side encroaching on the substance of the umbo, as in 7erebratula, Merzs- tina, etc., deltidium discretum, when the plates do not come into contact, as in Zerebratella, some species of Rhynchonella, etc., must be regarded as having no further significance than to express the existing condition of the foramen and deltidium in any given sfeczmen, that is, as indicating a stage of development, not necessarily a generic or even specific character. The observations of M. Eucene Drstonccuamps upon these features are of much value, and in most respects, as far as carried out upon related forms, are in harmony with our own (Note sur le développement du deltid- ium chez les brachiopodes articulés: Bull. Soc. Géol. France, 2° Ser. T. xix, pp. 409-413, pl. ix, 1862), but with his conclusions, we are forced to differ in some respects. The investigations referred to were made upon one (or more) Mesozoic species of 7erebratula, Rhynchonella, and Spirifer- ina, specific designations not given. The illustrations of Zerebratula (figs. 1a, 6, c, and column A, a, f, y, 6) show in effect the characters seen in Meristina nitida, Whitfeldia marza, and others; those of Rhynchonella early stages of similar character, resulting in a de/tzdium amplectens, such, as just observed, we have failed to discover in paleozoic Rhynchonelle. In Spiriferina, according to the author, the deltidium is produced by the gradual development of a single plate in the apex of the triangular opening, increasing downward with age, a very distinct mode of formation from all the others, and open to verification in the species described by M. Destonccnamps, as his figures make no allowance for a pedicle-sinus or perforation, a feature, though not of frequent occurrence in the Spiriferide, yet one necessary to account for. We have examined specimens of Spzriferzna pinguzs, Deslongchamps, S. rostrata, Schlotheim, and S. wadcott?, Sowerby, and find that these species, at least, develop triangular deltidial plates. Those in Spzer¢ferina pinguts and S. walcott2 are comparable with the same parts in Sperzfer perlamellosus and S. cumberlandie,and their form and mode of growth ¥ go MEMOIRS OF THE STATE MUSEUM - are expressed by the outlines 2”, 3”, on page 79, and is further shown in the accompanying illustration. Additional ! z growth causes the plates to unite along the /\ IN median line, obliterating the partially formed pedicle-perforation, and subsequent increment , , ‘ can naturally only take place along their rower /\ A TIN free edges, Fic. 4. DELTIDIAL DEVELOPMENT IN Our remarks on Sperifer radiatus and S. Dk Se aon crispus indicate that the development of the Se a ae plates in this member of the same family is quite in harmony with the process as seen in the rostrate forms generally. The following is the summarization of DEsLonccHAmps’s conclusions as given by himself : (1) The deltidium is one of the most important features in the articu- lated brachiopods. (2) As far as Jurassic species are concerned, the deltidium may suffice to characterize the families. (3) In the various stages of development of this part, the aspect of the shell is entirely changed. (4) The deltidium appears under three important modifications: A. development below the-peduncular arm, characterizing the Terebratulide, C. development above the peduncle, Spiriferide, B. mixed development, surrounding the peduncle, Rhynchonellide. (5) The stage at which the development is arrested or the exuberance of development may suffice to characterize sections under the families. It has just been shown that conclusions 2, 4, and 5 are not capable of the extended application which he has given them. A preceding remark, that the course of development of the deltid- ial characters throughout the genera here discussed, may be considered as fundamentally uniform, calls for explanation in its application to Or¢hzs and SILURIAN BRACHIOPODA gI the Strophomenidz. In the latter forms, we have seen that the remarkable development of the pedicle-sheath is primary, and is invariably more or less atrophied with age, and probably functionally inactive at maturity. Hence the retention of this sheath in any species at maturity is the perdurance of what must serve as an embryonic character within the limits of this family. It cannot escape observation that the pedicle-sheath is in analogy with the entire rostrate umbo of the ventral valve in the Rhynchonellz, Terebra- tulz, etc., as a specialized extension of the valve for the protrusion of the “pedicle (compare the extreme development of the umbo in the genus Terebrivostra). That these parts are also homologues, it is difficult to prove, on account of the pedicle-sheath becoming more degenerate as maturity approaches, but, assuming this homology, we may regard the sheath and its gradual disappearance, as an indication of degeneracy in the family, the presence of the sheath pointing toward a derivation from the rostrate type. The atrophy of an organ so highly specialized as the sheath, is, aside from any consideration of relationship to other groups of the brachiopods, it- self confirmatory of such degeneracy. Furthermore, it will be noticed, that there is, throughout these Strophomenoids, an inclination, as mature growth comes on, toward the simple triangular pedicle-apertures in Orthzs. The disappearance of the pedicle-sheath leaves the aperture of the ventral valve essentially free, as seen in Strophomena rhombotdalis and Streptorhyn- chus subplanum, while the aperture of the dorsal valve is filling parz passu with a callosity. In other words, the structure of these parts is actually degenerating toward maturity, to that of Or¢hzs, which is the simplest, least differentiated condition among the articulated brachiopods, and serves to fortify the position of the genus at the base of the entire series. In Orthzs, the pedicle-apertures on both valves are of the same size in early growth, and have undoubtedly acted together as a single opening, through which the fleshy arm was protruded as much on one side as the other, a fact indi- cative of an extreme lack of differentiation in the two valves in the articu- 92 MEMOIRS OF THE STATE MUSEUM late species, but agreeing closely with some of the inarticulate genera, e. g. Lingula, Leptobolus, Obolus. The specialization which accompanies subse- quent growth confines the pedicle more closely to the ventral aperture, and, as a result, the dorsal aperture is gradually filled by a callosity. Thus, also, the Strophomenide ;-but Streptorhynchus subplanum shows at maturity what has not yet appeared in Or¢hzs, viz., the initiation of deltidial plates, in conformity with the general course of development of the cardinal features observed in other families. It is not well in this place to go beyond the scope of this work, and the species of Strophomenide here discussed for facts confirmatory of our observations. It may be remarked, that the stage at which the development of the deltidial features has been arrested at maturity in this family varies with the species, not with the genus. When every trace of these features is obliterated, as is usual in Strophodonta, a slight abrasion of the apical substance of the shell will often show a trace of the obsolete pedicle-tube. At times, in the same genus, this is retained at maturity as an external feature, and in such a case is usually accompanied by some indication of the subapical sheath. In both Strophodonta and Streptor- hynchus (especially of the later paleozoic faunas), the cavity of the pedicle- sheath, if it be retained in any form, at maturity, has been filled by the deposition of calcareous matter about the compound cardinal processes of the opposite valve, and thus wholly diverted from its original function. In conclusion, it is to be observed, that of recent species of brachiopods a very great number show an incomplete development of the deltidial plates at maturity. Such is Rhynchonella to a large degree; also Czséedla, Argiope, Kraussina, Terebratella, and Magasella ; and we may assume the structural degeneracy which is thus indicated, to be the natural concomitant of the secular decline of the entire class. It is not improbable that from an early form related to the genus Orthis, phylogenetic development tended in two main channels. One TT aes “> il SILURIAN BRACHIOPODA . 93 leading through Strophomena, Scenidium, Orthisina, Leptena, Chonetes, Productus, and Strophalosza, and the other in the direction of Rhyuchonella, Spirifer, Atrypa, Retzia, and Terebratula. INTERNAJ. APPARATUS. Our observations upon the development of the brachial supports are limited to the species Retzia evax. Here it is found that the number of revolutions of the spiral ribbon increases with age, but we are not prepared to say what the inceptive condition of this apparatus may have been. In the early stage represented on page 60, where the ribbon has completed two revolutions, the supports must have been exceedingly tenuous and delicate, for they can be traced in the crystal- line or muddy filling of the shell, only by extremely faint lines, composed of minute dots of pyrite. As observed under the discussion of these features, the character or actual existence of the loop connecting the spirals was not established, but it is developed, with all normal characters, in a shell 4 mm. in length, where the ribbon makes four revolutions. It has been shown by Morsse,* that in Zerebratulina septentrionalts, the loop (i. e. the entire brachial support) begins by the development of two acute processes from the lower moiety of the dental plate, which assume the character of crura, eventually meeting and coalescing on the dorsal side, forming the completed loop at an early stage, the ventral horns of the loop never uniting. The simple nature of the support in these shells precludes the possibility of the continued growth which obtains in the more compli- cated apparatus of the spiriferous species. The inception of the brachial support was observed by Morse in an individual 1 mm. in length, but the lateral processes are not conspicuously developed until a length of 3 mm. is attained, and they have not united at a length of 4mm. It is therefore possible, from these data, that Retzza evax does not have the loop ¢om- pleted at so early an age as that indicated by a length of 2.5 mm. * Memoirs of the Boston Society of Natural History, Vol. ii; On the Early Stages of Tere- bratulina septentrionalis, pl. 2, figs 48-55. 1869. 94 MEMOIRS OF THE STATE MUSEUM The observations by Morse are corroborated by those of Dat1* on Terebratula cubensis. SuRFACE ORNAMENTS. Nearly all the observations upon initial shells or upon that portion situated at the apex of the beak of more advanced stages and representing the initial shell, seem to warrant the assertion that the surface ornaments do not appear until the second or a later period is reached in the development of the shell. For the plicate species, nearly the full number of plications appear simultaneously, as in Rhynchonella indianensis, R. acinus, and Rhynchotreta cuneata, or they are introduced in pairs, as upon Rhynchonella whitt2, ? R. neglecta, and Retzta sobrina. The strie of Strophomena rhombotdalis are developed to the full capacity of the marginal area as soon as the first growth-line is completed. The number is increased in three distinct manners, (a) by division, (b) by intercalation, and (c) by addition at the cardinal angles. Some species present all three of these, while others add to their striz or plications by any one or two of the modes. The concentric ornamentation in such species as Spirzfer crispus and Streptorhynchus subplanum appears early in the growth of the embryo, and continues to be repeated without variation, except in Strophomena rhom- boidalis and allied forms, which develop, during the last stage of growth, a geniculated curtain without concentric undulations. VARIETIES AND ABNORMALITIES. Varieties usually begin to express themselves early in the development of the shell, and the divergence from the normal form rapidly increases as maturity approaches. Several of the species represented by abundant material, are readily separable into three distinct groups of ‘forms, (@) dong form, (6) normal form, and: (c) broad form. The history of each may be clearly traced, and they * Proceedings of the Academy of Natural Sciences of Philadelphia, 1877, pt. ii; Report on the Brachiopoda of Alaska and the adjacent Shores of North-west America, p. 155. SILURIAN BRACHIOPODA 95 usually are found to unite with the line of the normal form (4), several removes from the initial member of the series. Sometimes the varieties do not reach the adult dimensions of the normal shell and may be con- sidered as varietal dwarfs. The representation of varietal and of certain abnormal conditions by complete series of fossil specimens shows, that in these directions, there was a distinct developmental tendency, or genetic impulse, independent of normal growth. SENILITY igalways expressed by the thickening of the shell which takes place after the individual reaches adult size. The thickening may involve the whole interior of the valves, producing a truncate appearance at the margins, or it may take place by frequent interrupted growth along the margins, giving to this portion a varicose aspect. As a result of this senile growth, the vertical diameter of the shell is increased, and the beaks involuted, so that they are often so closely appressed as to conceal the cardinal area and truncate the ventral beak, and in addition, the margins of the valves lose the characteristic ornamentation of the species and cor- respond to the clinologic and nostologic stages as defined by Mr. Hyarr.* Abnormalities frequently find an explanation in some pathological or accidental conditions which become instituted at any period in the life of the animal, and leave their impress on the shell. The functional failure of a developing organ may cause the parts to revert to an embryonal type, and although it is difficult to apply this statement to the shelly covering of the animal, yet this condition is sometimes found. The specimen of Rhynchonella neglecta described on page 37 is an instance of this kind. Another abnormal variation is noticed in certain individuals which preserve the larval features of the shell long after it has passed the early stages, and when, in many cases, it has reached the full adult dimensions. * Proceedings of the Boston Society of Natural History, Vol. xxiii, 1888; Values in Classi- fication of the Stages of Growth and Decline, with propositions for a New Nomenclature. , a ATA | = ACAISULII2 ATHARD ex Sar , “¥ and So7e Wihhe.& hice trea Yo aubsiail © uty eg ; Lerrmedy Leplily iba 9} yubene OTe : nyt alae ads do Siu) Reatines gene md Ai Nipde str Sa. ant au muni? Ve fyndd yiffe) omAedetS. ty Ted k OF by sdonatns Sag hiteBed Groret Jr ox ngs SIU HA ani ; > a va opal a f “Sa A iy sie oo? Se th - Fa _—" mz cststond diye an tS = as ie woe 7 tdi: vheg saad? dnd heart © chee cult Yo atinowy oie = tS = Kc ae OD ihatel vv Ww deve oy ere Piha fo qlevoran. rihits Wildyile vil gators 5 lala SP tte ett ele anes att sowrit hewraly hynteos veprel # + pa pige eral atnley JO eho ATi, 6 le Hanamyatissh Ww riggs Citar Sell Yuin ri evlivitnt na lo wety Iino q 2th _ efrathiedly Lert to etiam yore lem reste be aigh calt eo Mire ase! datos wT aconte dterety odt nl Manbivibot ae feet lenin) * se relia! ot T et wl oun ea * ald apbsiideny ret fo caplet Aura ccrte Mineilirens wl! to dit add olidw os c Hey Ashe w nosks goitetadietels volta wor? » fend bao tiedonu otha ny } Si Te pate ~ wales geniitv® «i ott ; od) W! aur “6 wma vl — Oe te att tputw teuhivibal na Te Siti: as ST arviav oft Wo mewoere) hae 2ovn hone oa XPLANATIO yN- OF ‘PLATE 2A sa sont e > Dresie p te Were ‘tantlyeass a 3 atu zord? crnl boblvihdug . -2unne Gil) 20 stitorg wilh wi wits ” vytionun edt ot teow ta wt * “eo do teen ptamett gemiceed eet daind Jewry oft « csierys HD te Sie Levetian gid geereypgig. sori-atots off unre 4» et hens & tn wale UE .g oh tea lhiy atten» a Del > a Oteeny anllinO .ve oa 19a qhoeghs ate aacte oT acc, 244 0 ele pr » Wo Weir ewig? or lt ae ath ated whenstes fottw jo te D0 Lexus of! »uotrrg Laolb yas oA) vd 2; atte od 16 ofitong Saito ox oT gi Linehan (tute Lnarron «Yo wole baile) a1 ay wat nome bmx ovles Laxtows oft aero Genitrur — VSies 9% seareenet > Peete he te seam sift in alton") vw f aA al site @ Wo whi Littl 205 5 ow pr ex ag? Agu ws wate Casio mt — ‘a ~—" - “ “ _ ee ‘ ydrowoe AMARYL ett zO — P cont De siheien grat grey a to wate Leming gr gt Syren « Hie yk oy OCI Be : rime ait) $0 elite wit4nO Dimes th: phvmcss dankig tel wen » ee ih) 53 ‘a a; Les inaitrsao oft bite Awyolsy oom os Wot trog abe) ~~ wt sa) Virb beeen a be wesiy baba gr P tot regs lachone tert guiwods slong satlheO eee gett: cles i) Als vaghdiee sqeel « Yo wotr Lert] te gre its gibt eibathe Learrec & to alton ont ‘oe Shon nescence a aie 8 Yo ware ber .ab + te wens So Mryest« prised 1 oe eo Ay des Angas guilt oily ile iI naa ¢ AERO. " 1) opt Sy faetels cal? Lo vite +E OF 3 ity hare eed Prods oil) gntn cote cous wl) > vy tay TES e = =) eos alah agony Aerie gare ee Sehahet> Sa) AN at a gaan s sf to siterT AY sah? a b a t_-= ‘ ee, Seo: a gS ee wl Fe evar , e z ee? ‘ f 7 * oe . . ul "7 cy ‘ rs ‘'- * 7 j 4 ~ 7* x! ~~ a [ e " Lay a Te — af? b> "a a Ss pS raya ie 3 : a. De , 43 os “ac” | om : : | | it oe js Ct | 2 } ‘ ‘ Fig. 5s. PLATE I CRANIA SILURIANA, Hall Page 13 5 . The youngest individual observed; having a height of 1 mm, and a width across the base of 1.5mm, The elevation of the shell is in strong contrast to that of the mature form. . A mature individual attached to a shell of P/atystoma (28th Rept. N. Y. State Mus. Nat. Hist., pl. 21, fig. 5). ORTHIS ELEGANTULA, Dalman Page 13 See Plate viii . Dorsal view of the youngest embryo observed, its length being.5 mm.; its width.75 mm. The median sinus has already formed, and three pairs of plications have appeared, of which the middle pair is evidently the oldest. . Outline profile of the same; showing the slightly greater convexity of the ventral valve. A larger example viewed from the dorsal side, its length being 1 mm., its width 1.5mm. The plications have now in- creased to the number of six pairs, one of which has appeared between the median plications seen in fig. 3. Ventral view of an individual in about the same stage of development; showing a strong median plication corresponding to the dorsal sinus, and five pairs of lateral plications. Cardinal view of an individual in the growth-stage represented by fig. 5. The valves have nearly the same convexity, while the width of the cardinal area and the size of the pedicle-passage are the same for each, The latter is seen to be quite unobstructed and without further differentiation that a slight thickening of the margins. . Outline profile of the same. . Cardinal view of an individual which has reached a size of 3x3mm. Here is apparent a change in the development of the cardinal area and foramen of the valves. The primary indication of the callosity or cardinal process is in the apex of the dorsal openi The difference in thé convexity « of the valves al ceably increased. Outline profilé of the samé. _< Pe i aT tage . Cardinal view at a size of 5x5 mm. The ventral beak has become strongly incurved, and the cardinal process is now subdivided into three parts. The cross-lines, representing the natural size of the specimen, are too short. . Outline profile of the same. Cardinal view at a size of 12x11 mm. The ventral valve and area have become greatly curved, and the dorsal aperture is quite filled by the tripartite cardinal process. . Outline profile of the same. . Cardinal view of a large adult, size 18x 18.5 mm, ‘The areas are closely appressed, and the dorsal aperture is wholly filled by the cardinal process, the central portion of which extends into the aperture of the other valve. . Outline profile of the same, . Cardinal view of a normal adult; natural size. . Profile of the same (of. c7#. pl. 21, figs. 17, 14). . Dorsal view of a small adult. . Ventral view of the same (of. c#t., figs. 12, 11). ORTHIS HYBRIDA, Sowerby Page 17 Fig. 13. Cardinal view of a very young individual having a length of 1 mm. anda width of 1.5 mm. The valves are nearly equiconvex, the area and apertures as in the earlier stages of O. elegantula, Fig. 134. Outline profile of the same. Fig. 14. Cardinal view of a somewhat gibbous example measuring 10x8mm, The relatively short areas are about equally de- Fig. 142. veloped, and the cardinal callosity of the dorsal valve has already filled the dorsal aperture. y Outline profile of the same, Fig. 15. Cardinal view of a normal adult 12x 10 mm.; showing the short area and the projection of the cardinal process into the ventral aperture. Fig. 154, Outline profile, showing the incurvature of the areas. Fig. 16. Dorsal view of a large adult (of. c7t. fig. 20). Fig. 17. Fig. 18. Fig. 182. Profile of a normal adult (of. eft. fig. 21). Dorsal view of a small, gibbous example, showing strong varices. Enlarged to two diameters. Profile of the same. ‘ap. Beet C EL LOL ODA... MEM.N.Y. STATE MUS. PLATE =z. 6 ; _ Wy - 1 Ta ss coer + \ | a cu ( ei} a ‘A \| ~ = Wa ox zt lla 12 a il y “4 Ma 3 “a - a 4 {’ ‘ \ Si v \ < \ | 7 { \ a | | | 9 } i | 18 wa % YN Philp Ast,lith Weed,Parsons & Co. Albany, NY. ~ ‘ ? & > “ile a = Gan i ' r va ‘ - Il ATAI4 ALIACIONMONA “AK tet te wm Ati’ ei bern ded qrey ety deme Talnnss Genes sone! YW asses od a _— 4 nesteedls Gol ae Se sb ath 00 Dengue. i.sies . ‘mgeayt ‘Saat aie earned seasons Sates aihnp ct sa 9B 8 st AP si om ae ¢ dla! . Wer SM) ytieclined eviews ihestle > red eon ties ah ie ytirerp whe galwode prem ott ie Sain Werte Yo yia1=t ne Abe peta) es piel nw Poly upton’ wt at % PLATE II STROPHOMENA RHOMBOIDALIS, Wilckens Page 18 Fig. 1. Ventral view of the youngest shell observed, its length being 1.2mm. The aperture of the embryonal pedicle-sheath is very conspicuous, and its margins very thick. The surface shows a faint median depression, indications of two con- centric growth-lines, and outside the latter of these, obscure traces of plications. Fig. 1a. Outline profile of the same, showing the prominence of the sheath, Fig. 2. Ventral view of an individual with alength of 2mm. The aperture of the pedicle-sheath is relatively somewhat dimin- ished in size, its margins have become thinner, and the radiating plications numerous and sharply defined. Fig. 2a. Outline profile of the same, indicating diminution in the prominence of the sheath. Fig. 3. Ventral view of an individual having a length of 4 mm.; showing the increase in the number of plications, the appearance of ‘ous ic undulations and striae, and the narrowing pedicle-aperture. Fig. 3a. Outline profile of the same, showing the concentric undulations and the diminishing pedicle-sheath. Fig. 4. Ventral view of a normal adult, natural size, having a length of 28 mm.; showing the characters of maturity. Fig. 42. Profile of another individual of full-growth; showing the anterior geniculation and the length of the anterior slope or curtain. (28th Rept. N. Y. State Mus. Nat. Hist. pl. 22, figs. 6, 7.) Fig. 5. Cardinal view of the specimen represented by fig. 1. Fig. 6. Similar view of the specimen represented by fig. 2. Fig. 7. Similar view of an individual 2.65 mm. in length Fig. 8. Similar view of the specimen represented by fig. 3. Fig. 9. Similar view of an individual 9 mm, in length, These cardinal views are drawn with the same degree of enlargement, and show the gradual diminution in height and in diameter of aperture in the pedicle-sheath, and the increasing de- velopment of the grooved callosity on the dorsal valve. Fig. 10. Cardinal view of a normal adult, natural size; showing the great size of the grooved callosity, and the cacal opening, Pig The ca abarea efron tx Ref cede Seams ile nf wi fe podrominnt, eer ens at its base, the Fane grooved dorsal Fig. 12. Prag cardinal area shown in fig. 6 (length 2’ mm.), enlarged to the size of fig. 11; showing the depression of the sheath, the narrowing of the cardinal area, and the increasing aperture between the sheath and callosity. Fig. 13. The pedicle-area of a mature individual, x2, The sheath is now wholly absorbed, the sole trace of it being seen in the caecal foramen, surrounded by the umbonal portion of the shell. The callosity is strongly developed, but not suffi- ciently to close the gap between it and the opposite valve, thus leaving a passage between the valves and along the dorsal groove. STREPTORHYNCHUS SUBPLANUM, Conrad Page 23 See Plate viii Fig. 14. Ventral view of the smallest individual observed, having a length of 2.2mm. Both primary and secondary plications and concentric growth-lines have already appeared, indicating the very early ee of these characters Fig. 14a. Outline profile of the same; showing the convexity of the valves. Fig. 15. A normal adult, dorsal view. Fig. rsa. The same in profile (of. c##. pl. 21, figs. 30, 31). Fig. 16. Cardinal view of speci somewhat larger than that represented in fig. 14. The ventral valve bears a small pedicle- sheath, the dorsal, the inception of a cardinal process or callosity, while between the two is a broad opening, which serves to indicate that, at this early age, the pedicle-sheath had ceased its function, Fig. 17. Cardinal view of an individual slightly below normal full growth, but with essentially mature characters. Fig. 18. The pedicle-area of the specimen represented in fig. 16, Fig. 19. Pedicle-area of a shell having a length of 4 mm. At this stage of growth the sheath has relatively diminished in size, while the dorsal callosity has increased and shows a median groove on its inner edge. Deltidial plates have also be- + gun to develop along the margins of the ventral aperture. Fig. 20, Pedicle-area of the specimen represented in fig. 17, The sheath is now atrophied and altogether obsolete, the dorsal callosity is very large, nearly filling the aperture between the valves, and the deltidial plates have attained the max- imum development observed in the Strophomenida. The last three figures have the same degree of enlargement. = RACEHIOPODA ‘ MEM.N.Y.STATE MUS. PLATE XZ, Pmilip Ast, lith Weed,Parsons &Co Albany. NY ve PUA Se. _ ‘ +5 pie hy re as Sa a of or sr ate ot , ey ee epee ae | avd dtesds ont emo” basen tLawtaae et : 1 baw soit ‘eal arias ae “ Vewsty anti: a ke ee ya gunne oth wore lewd v 6 Pet a, aR qeare sate waly linus ni sie a AIUAW Ha se opel 4 “4 span peveate esmalcoeeye Seowre' old . are tastings (oa tet Inno? lo abilevsto 28) gaiiwode has Se ag seed q alow awd taba 2a Mi wesley sis'%6 ha HO“VH St sibvA site) Dvd eoditvouy ditt b> PN Taaeerpvicveten Bata Bo’ otald 00. as mil aa en v nal siete tr Labonte storm G pen Fat més ail Yo ion ba mat spe nl W sdretha cd? “ttgiel cam 7 6 Leobl vibe o6 at ested ase PY done eDagiis rs heprtraent brad doi eviady (athition adit ‘4 - routine sid Yo see au MnO ge lt Lt tdng atone ait gnived- ails uc bt eecuies! Lanlly fis cot ee Ot a Lavery ot edt te vldeny eotivO te oft stat Sat em Pan AN s is Fig. «. PLATE III : STROPHONELLA STRIATA, Hall Page 25 Ventral view of the incipient shell of the series (length 2.25 mm.); showing the opening of the pedicle-sheath, and the mary surface plications ; Fig. 1a, Outline profile of the same; showing the complete convexity of the ventral valve, and essentially confarmable concavity Fig. 2. i 3. ig. 4 & me & Fig. 9. Fig. 9a. Fig. 94. oe Fig. 10a. Fig. 106. Fig. 11. Fig, 12, Fig. 13. Fig. 134. Fig. 14. Fig. r4a. Fig. 15. Fig, 16. Fig. 162. Fig. 17. Fig. 17a. Fig. 18. Fig. 182. re: 19. Fig. 20. Fig. 21. Fig. 22. Fig. 23. Fi, ig. 26. Fig. 26a. Pig. or. Fig. 274. Fig. 28. Fig, 282. Big. age. . 24a. Fig, 25. Pe- 25a. of the dorsal valve. Ventral valve of a_ normal adult; showing the umbonal convexity of the shell and general concavity over the pallial region. (a8th Rept. N. Y, State Mus. Nat. Hist., pl. 23, fig. “4 Outline profile of the same; showing the reversal in convexity from the embryo condition. Pedicle-area of the imen represented in fig. 1 (length 2.25 mm.); showing the well-developed, slightly exsert sheath and the obscure dorsal callosity. Pedicle-area of an individual, 2.5 mm. in le in which the sheath is extravagantly exsert. Pedicle-area in an example about 6 mm. in | : Pedicle-area, when a length of 8 mm. has been attained. Pedicle-area in a shell measuring 13 mm. in length. . ~ Pedicle-area in a normal adult measuring 17 mm. in le u Figs. 3-8 have been drawn to the same scale, and show the successive phases in the development of eating is characters. The sheath ceases its function as a pedicle-passage before maturity is attained, though its relative size, while the dorsal callosity, which in the earlier stages is grooved and largely enveloped b sheath, is eventually separated from the sheath by a narrow aperture, and its surface becomes uninterrupted. STREPTIS WALDRONENSIS, Miller and Dyer 5 Page 30 , Dorsal view of a young individual having wn a of 3mm. The shell is nearly symmetrical, and shows an open triangu- lar deltidi ding in a subcircul ory ‘oramen. Ventral view of the same; showing the apical foramen. Outline profile of the same. Cardinal view of an adult specimen; showing the asymmetrical shell. Dorsal view of the same. : Ventral view of the same. (11th Ann. Rept. State Geol. Indiana, pl. 27, figs. 21, 19, 20.) EICHWALDIA RETICULATA, Hall r Page 3: A young individual havin x length and width of 3 mm.; showing the subcircular outline and undefined median fold. 2 aH fold Axial jon ofya lar, ya sat in egeing oo as of se ia a and ho: fa ternal ventral slate and dorsal Spi ay P ‘ys Yi “y1 i > et 2 T fon.) ¢ Cardinal view of the same; showing the bare umbonal area and the lines of lateral attachment of the internal plate, x2. (Figs. 13, 13¢ from the 28th Rept. N. Y. State Mus. Nat. Hist., pl. 26, figs. 53, 54.) ANASTROPHIA INTERNASCENS, Hall Page 32 Ventral view of the youngest specimen observed (length 2 mm.), Outline profile of the same; showing the elevation of the ventral beak and cardinal area. Dorsal view of a large adult. Ventral view of an average adult; showing the veteres dorsal valve. Profile of the same; showing the relative convexity of the valves. (Figs. 15-16a from the 28th Rept. N. Y. State Mus. Nat. Hist., pl. 26, figs. 49, 45, 44.) RHYNCHONELLA INDIANENSIS, Hall Page 42 The earliest stage of growth observed, the shell having alength of .65 mm. The characters are essentially primitive; the surface is without plications, the foramen —— and devoid of plates, or even marginal thickening. Outline profile of the same; showing the elevation of the ventral umbo. . A later stage of growth in which the shell has a length of 1.5 mm. With the formation of the first growth-line, a number of faint plications have appeared, and the margins of the foramen have become thickened. Outline profile of the same. * A young = with a length of 6 mm.; showing the inception of the median fold, (11th Ann. Rept. Geol. Surv. Ind., pl. 27, fig. 6.) _— view of a larger {zemole. natural size, having two plications on the fold, and abnormal in the absence of all lateral ications (of. c7t., fig. 5). Dorsal view of a small, conattelhy mature example, with two ag peri on the fold (of. cét., fig: 4). Dorsal view of anadult with three plications onthe fold. (28th Rept. N. ¥Y, State Mus. Nat. Hist., pl. 26, fig. 13.) Front view of an adult with four plications on the fold (of. c#t., fig. 22). view of a similar individual. Profile of the same (of. cit. figs. 15, 19). An pny mag the cardinal area in an individual with a length of 1.5 mm.; showing essentially the primitive charac- ters seen in ~ 17 Outline profile of the same. ‘ The condition of the ventral cardinal area and foramen in an individual 3.5 mm, in length. The margins of the foramen it thickened by the inception of the deltidial plates and the aperture is seen to encroach upon the apical portion of the Ss Outline profile of the same, The cardinal features in an individual of 7 mm. length. The advance upon the last stage is chiefly in rapid development of the deltidial plates, which have narrowed the opening, slightly constricting it near the now incurved umbo. Outline profile of the same. The cardinal features in an adult, having a length of 1omm, The deltidial plates have united at their base, forming an elongate oval aperture, encroaching upon the umbo. The species does not pass this stage of development. Outline profile of the same. Sr ACP IOLFOoDsA.. MEM.N.Y. STATE MUS... PLATE rmt.. 1 la 2 Philip Ast,lith. Weed,Parsons & Co. Albany, NY. > : < > f >. 5 4 ? a ~ ae wa ‘ iPod ® bad 4 ..¢ ELOePOmA eo ee Hohe ae Veet view «> 3% es P tose 2 gil Saas Dh p rt, ~*~ Wa} eon a ae rh pas tesk Pin t a Dryas pry fy 7 ae rut = Ws Pe mw 8 Yer thie sh a 3] ma oat y —— cm } = - = — tite Pot) pe bette dues oo znligrae Lecragiddy 2 vay uta | ~ © dw inne ibed.« de Mowery lees oy iT ae avn suet o wig be aod some edt Yay omy pavittan) iy Lvens(T es w oD 7 heaeal on welt prac; seyo.dt ger; otttr, ates noruhy | act thee Lacey na su | ps TO ALTRI oe > ae ia: wt ne ; iprcnstgale » lin ybe atin ha wate Tutte 9 mi Sede qoutes 2 Yo voir on » wet a : r ny 3 vba eet au sree wit) Ty ste ened eg at ig , +4 F PLATE > ee Dy cm " ot it PL * GomPenga io wore > es Be tr mo Gem ern grits 367, zine sift to wi =n — = , onlgig Abe? yiivtyile ime nme) eat te oly ¥ twos wd? to iv om nin me ) By: -* Heke sgeryre on ‘ane ’ ety ac, ; hen eathnes ult fe a rely erty qurwoke pateae ees " . 2 . ans a ve " AA “~. bo > aie “a uA i are r — 4 iy gee esl at ti wale. ert a yt ’ ail - boast et ma foals y On att 2 erveet acevo) =! stein : ; , st ' PS a i Sap reaese tera ane ws nad Aouts a p sy is iF f belt Bi ON Lew. ah ott ay afore ; a aa ee wow ee : : re i 3 ” ca} wren ee } a lang , 2) weernri cee | ch we pe coun et morn 7 wn otti tape 4 We treteeols yews ayrendns piers online s : 4 - ike AS Ww meen Minne "Hert cz ih amet —" oi arnt a9 cites ee - wows wan ye nil aap Paewrercsh ade Lo dreene : 4 ai ) } vamey a anal 5 wu letras 9 7 j yo v \ y netilbedt A P -*s nam x59 Sonal Ato eee ta 1h oo 2 ee en : Bows aq its an ys i é Yondetts” cnet devistye budlowiiinnl new) devid Lap Ue oe Pe ae! ‘ali ips ride) ape a yril emake <7 there i wente ‘4 at “t m Flimake orld We -aage Trae | 4 An yhirow] only ave ‘an rah . akwaterot ovbr hy pre alt: deherda Leet ier 2 fain adt woted minor tm votewh —; oa » we x Le. 5 t “~ aie — oF > 47> & . AIIIKO a A ‘e omet - ; 7A ei p Dsile ots Be te ogre bey werin testifies oT x | gill | iat ~ teyhe is Specie Wit ever yhuatia sve + 5 ¢ asvley teeab ' gre 2h wesliegy colli ws yt. 4 ow i} tt E ube Sh oS Fig. 6. Fig. 6a. Fig. 7. Fig. 7a. Fig. 8. Fig. 82. Fig. 3 Fig. ~, . Dorsal view of the same. : Outline profile of the same . Cardinal area in an individ PLATE IV RHYNCHONELLA WHITII, Hall Page 39 . The earliest observed stage of growth, the shell measurin; A Beg in length by 2 mm. in width. The deitidial plates angu have already begun to form along the edges of the dorsal valve. Outline profile of the same. Dorsal view of a normal adult having two plications on the fold; natural size. Profile of the same. Front vjew of the same. (28th Rept. N. Y. State Mus. Nat. Hist., pl. 26, figs. 23, 26, 25.) fa eer gs features of a young example with a length of 3.25 mm.; showing the inception of the deitidial plates. je of the same. Cardinal features of an individual which has attained a length of 6mm. The umbo has become incurved and the devel- opment of the plates is well advanced, but it is arr at this stage, the foramen not becoming inclosed at maturity Outline profile of the same. RHYNCHONELLA NEGLECTA, Hall Page 37 Dorsal view of the youngest shell observed, having a length of .75 mm., a width of .5 mm. ity the foramen is open and without evidence of thickened margins, four fine plications have already ap on the dorsal valve, Outline profile of the same. . Dorsal view of an individual with a length of 2.25mm. The deltidial plates are in an incipient condition, and the plica- tions of the surface have considerably increased. Outline profile of the same. Dorsal view of a ple; I size. The same in profile. (28th Rept. N. Y. State Mus, Nat. Hist., pl. 26, figs. 3, 5.) A somewhat abnormal adult, having three plications on the fold and the plicati Rept. Geol. Sur. Ind , pl. 27, fig. 3.) foramen, and four pairs of plications are visible on the obsol » x2. (11th Ann, RHYNCHONELLA ACINUS, Hall Page 35 Ventral view of a young shell in a secondary stage of growth; showing a single growth-line and the embryonal median sinus iswell di J ridge. % Dorsal® view of the same. The foramen is slightly narrowed, but without ye aes t or ES a the embryonal yy, Tc] iz f : ‘ . Outiine/profile of the same. lI) AOTLTAYALTTA. ; Ventral view of a specimen 3.25 mm. in length. The mature fold and sinus have not yet begun to develop; the foramen shows increased con- striction at its base, and slightly thickened margins. . Outline profile of the same. . Dorsal view of an average adult, x 4. . Profile of the same. Front view of the same; showing the elevation of the median fold. RHYNCHOTRETA CUNEATA (Dalman), var. AMERICANA, Hall Page 47 See Plate viii Dorsal view of ashell resenting the earliest e of wth observed (1 h x.5mm.). The foramen is widely tri- angular and iapbalracted; the purtace is poh with » all the plications ob ata, and the subcircular valve a broad median depression. . Outline profile of the same. . Similar view of a shell3 mm. in length. The outline has become elongate, the foramen narrowed and its margins thickened. . Outline profile of the sam ec. jew of a normal adult individual, natural size; be ed the elevated beak and broad plications. . Profile of the same, showing the ele vation of the dorsal fold. . Front view of the same (28th Rept. N. Y. State Mus. Nat. Hist., pl. 25, figs. 31, 34, 36.) j . A series of outlines of the anterior margin; showing the embryonal sinus or depression in the dorsal valve in young forms, reaching its maximum in individuals having a } of 4.5 and becoming obsolete, or the line of junction straight, in specimens 7 mm. in length. Outline 6 shows the inception of the dorsal fold, In 8 the four median pli- cations are distinctly elevated ; 9 is from a normal full wn individual and ro represents the maximum elevation of c bd ger be outlines, except in 9 and 10, are anlargot to the diameter of a fully developed specimen. ar area 0! . 12. ; Satine pox of the same. area of fig. 13. ual 4.5 mm. in length; showing the considerably advanced development of the deltidial plates the of Hi én on the apex of the valve. y an . Outline profile of the same Cardinal area at a length of 5 mm. ‘9a. Outline profile of the same. Cardinal area at a length of 7 mm. . Outline profile of the same. . Cardinal area in an individual which has attained a1 of 12 mm. The plates are united for nearly one-half their length, and slightly bent outward about the base of foramen. . Outline profile of the same. G nal area at maturity; showing a stronger flexion of the plates below the foramen, and a subcircular foramen, en- ing upon the apex of the shell. croach . Outline profile of the same. "i om LO ODA... MEM.N.Y. STATE MUS. PLATE sv. ® @®@ 4a Philip Aat,lith Weed,Parsons &Co. Albany, NY Soren Haar vabergse oe we skis owe we | aries et +) Se anh fealPice ep oi ee ate 7 th iP s our 30d wstet {nt wide a pose 1. tite wr taal ais h at aaeeee or he twubsl vitor! 0} fo keeling Ieotheer sd! 5 oft re » Naar eerU yer Ook Eres Alt. genet py in bens gilvtun ont? YO where fT 2 Py pe Le teww sty b hae ie A ar a) stu _ ie games i Be ms = in - A ,. | ¥y ny f ’ bs |) in. p bolle ates (td © Ye Dpgerel @ gehen termed M4adp = er wT ¥ pa ATION OF Freche en: Bas ure rarer ra mit porta sad weemca eres ies os Wi erate herp, oi at a oe yl! of oqesap ny Our ts Gyteprets aT gt xf Meweretagt ‘ate ot Seperr} tal? we ~ alr irae ett bo othong wittlwO .mee yl . bevdyrt htaesiiioon wis asialy ty dbiviw GPWoty Be cigets toned A gt GV ene 01d Yer oftremy wlinO oes aw fo eat es ae wabanbe out0- wal and teormens) Gi) Shite oi doworg ys . ees nl Yas add Deen Sipe tinay doldiw > oe mana $8} \o at Wilt po ne—rdiben pdt to aot rthawe 7 we. < 1 eee Ss ; = a why ee oe 7 roe a8 7 - ie ea) now Us one eames owt > y ye co ‘Riana. : j ful. suet: =| : o > i a eo ery wie ny Ja at } dha ~~ come ot Yo Aye war 1. ek AF ae pevirnast shat 24) es awed ) Att. ane e / srt a Lara vnivchalt ba wee tegen OP ean ee se ges sa ' : piasisid> altod be . au) pays ack bei rn . evtler wolle Pee 2A) ent woile -puver SA a at ftoreg wOIWO Jere - wt sta weeny wy trsaorrebyrab pas a repmmrens aninoda Ioybiviinl govog A gl =, Aengtiefee hart Deere onl? ni tot anit ae a y 3 thats herted & VRohy (ee oo = ogi -? : - ae he orgie LenS ge aT : e 4D A) _Ayptewnmats Cord er texyaleen wre CLA seam aid Yo wien Roe yet . pe wets in, ont oo antag Laekictin sh pm 1) ¥ hae a ee aut ’ * sede da eh eaigit te ell doithw = ae hy prone ‘ a oN F s he al r * . ; .; 7 Ms 4 aw : | y y . ; PLATE V : RETZIA EVAX, Hall Page 55 See Plate viii Fig. 1+. Dorsal view of the youngest individual observed, having a length of 1 mm. anda width of .8mm. The ventral umbo is erect, the foramen triangular and without deltidial plates; the surface bears two faint lines of growth, and outside the second of these, are three fine plications on each 'side of a median sinus. Fig. 1a, Outline profile of the same; showing the very shallow valves. Fig. 2. Dorsal view of an average adult, showing the characters of advanced growth. Fig. 2a. Profile of the same. (28th Rept. N. ¥. State Mus. Nat. Hist., pl. 25, figs. 14, 18.) Fig. 3. Dorsal view of an immature individual, 5 mm. in length, in which the plications on the earlier portion of the shell end abruptly at a growth-line, from there outward the surface characters being altogether primitive. Fig. 34. Outline profile of the same. Fig. 4. The cardinal area in its earliest observed condition ; enlarged from fig. 1. Fig. 5. A later stage of growth in the cardinal area, the deltidial plates having a considerable development. Fig. 6. A still later condition of this area, in which the plates have united, enclosing the foramen. Fig. 7. The cardinal portions of an individual with an unusually elevated ventral umbo; showing also an advance in growth from the condition represented in fig. 6. Fig. 8. The character of the cardinal area in a normal adult of about the size represented in fig. 2. The foramen has become circular and the ventral umbo so incurved as to conceal the deltidial plates. Fig. 9. A small obese example in which the foramen is almost wholly concealed. RETZIA SOBRINA, sp. nN. Page 61 The youngest shell observed, having a length of 2 mm. anda widthof 1.6mm. The shell already bears two plications on each side 6f the median s, and uch fainter ‘ize inthe Sinus itself." 7 ~ Fig. 10a. Pv. 333 oF A a 2 . rt rt i] raat TT ron A a It 4 4 Fig. 11. Dorsal view of an adult specimen, somewhat above the average size, and enlarged to 114 diameters; showing the normal features of maturity. Fig. 11a. Profile of the same. Fig. 114. Ventral view of the same individual; natural size. Fig. 12. Transverse section of an individual; showing the spiral ribbon and the number of volutions. Fig. 13. The character of the pedicle-passage in the youngest example (fig. 10). The deltidial plates are absent, but the margins of the foramen are thickened. Fig. 134. Outline profile of the same. Fig. 14. A later stage of growth, in which the plates are considerably developed. . Fig. 14a. Outline profile of the same. Fig. 15. A stage of growth in which the f has b ircular and apical. The plates are slightly flexed along two oblique lines which converge toward the base of the area. Fig. 15a, Outline profile of the same. Fig. 16. The mature condition of the pedicle-area, the deltidial plates being somewhat concealed by the incurvature of the ven- tral umbo. Fig. 16a. Outline profile of the same. The drawings 13-16a are drawn to a scale. CCELOSPIRA DISPARILIS, Hall - Page 64 Fig. 17. A young individual 2.5 mm. in length; showing surface and pedicle characters, essentially as at maturity. The sinal plications apparent at this early stage, appear, in the usual adult form, as the broad median fold. Fig. 17a. Outline profile of the same; showing the erect beak and shallow valves. Fig. 18. A young individual; showing asymmetry in the development of the median fold, and a greater number of lateral plica- tions than in the normal adult (enlarged). Fig. 19. Dorsal view of a normal adult. Fig. 19a. Ventral view of the same. Fig. 194. Profile of the same. All are enlarged to two diameters. (28th Rept. N. Y. State Mus. Nat. Hist., pl. 25, figs. 39-41.) Figs. 20-23. Enlarged views of the umbonal region of the ventral valve; showing the variations of form and position in the foramen as observed among specimens which differ but little in actual size. fe een St tO ODA... MEM.N.Y. STATE MUS. Le? Abie te Ws tT na + Philp Ast. iith Weed Parsons & Co. Albany, NY. Kutt eet SL ee eee , S Pihas gilt We ello snitteo hoe bevivado siqmues eagniiey oT us 1 zgiF - f memes onal wo weiv leno 2 yi Les a a tat fon aaa Joo dint &™ Sinse oft to way Tealb) 5 po eGo > greene dt patuteqga nto wAby whinni® ax aw ’ ‘z octet Vay ofttorg ante) wet * t. m pete ey 4 (me # Yo waiy ioe 2 . atte { \sbarepa-o9td To ola’ act ath A aw 3 wines pomtrnp » Oo mt) a * pores ant In ofitory eaitiv’) 108) il < By oS ae | prt tanees or ahinkesye by wvoty refial? .g2 } jot ; mm ott to olhong ontiwO .eef ait = = sk tes ps ENR SUMiaye OWoT ET # Wo veoty Walia? ox ) yi ='Se won atl) Jo een sniiwoO en > aad & ‘ t — __ Pi \ - a ‘ J ' is . >» _™ ~ } > MEE, Tl, . Tl, | PLATE VI SPIRIFER BICOSTATUS, var. PETILUS, Hall Page 75 Figs. 1, r@, The youngest example observed, and outline profile of the same. Fig. 2. Fig. 3. Fig. 4 Fig: Fig. 5. = = a Fig. 8. Dorsal view of a large specimen. Cardinal view of the same, x3. (11th Rept. State Geol. Ind., pl. 27, figs. 8, 9.) SPIRIFER CRISPUS, va7. SIMPLEX, Hall Page 75 Dorsal view of the youngest growth-stage observed. Within the single growth-line, the smooth subcircular initial shell is visible, but outside this, the shell has developed the median fold and the surface fimbriz. . Outline profile of the same. Dorsa) view of a mature individual, x 2. Profile of the same, (28th Ann. Rept. N. Y. State Mus. Nat. Hist., pl. 24, figs. 1, 4.) SPIRIFER CRISPUS, Hisinger Page 75 . Dorsal view of a young form, in which the deltidial plates are in an ong condition. . Outline profile of the same. . Dorsal view of a mature specimen. 7a. Profile of the same, (28th Ann. Rept. N, Y. State Mus. Nat. Hist., pl. 24, figs. 8, 12.) SPIRIFER NIAGARENSIS, Hall Page 80 The cardinal area of a ventral valve, from Lockport, New York. The deltidial plates are in the third stage of develop- sgh tt ia pe ihn hei ae Sara a SPIRIFER RADIATUS, Sowerby Page 77 . A cardinal view; show oe a similar stage of development of the deltidium; from an individual which has not attained normal full-growth. . The youngest growth-stage observed. . Outline profile of the same. . Dorsal view of a normal adult. . Profile of the same, (28th Ann. Rept. N. Y. State Mus. Nat. Hist., pl. 24, figs. mes ATRYPA RETICULARIS, Linnzus Page 51 . The incipient shell, having a length of 2.2mm. The deltidial plates have already begun to form, and the shell has de- veloped two growth-lines. . Outline profile of the same. . Ventral view of a full-grown individual. . Profile of the same. (28th Ann. Rept. N. Y. State Mus. Nat. Hist., pl. 25, figs. 46, 47.) . A series of outlines of the anterior margin of the valves; showing the rapid increase in plications and the reversion from the embryo fold and sinus to the sinus and fold of maturity. The deltidial characters of the specimen represented in figure 12. . Outline profile of the same. . Similar view of a specimen measuring 3 x 3 mm. . Outline profile of the same. . Similar view of a specimen measuring 3.5 x 4 mm., . Outline profile of the same. . Similar view of a specimen measuring 8x7 mm. ° . Outline profile of the same. ; . Similar view of a specimen measuring 21 x 20 mm, . Outline profile of the same. . Similar view of a full-grown specimen measuring 24 x 22 mm, . Outline profile of the same. ~ » ~ h “~~, = Ni " “ . % ¥ ' “— Be A in SE a ae he ae MEM.N.Y.STATE MUs. PLATE vir. oie dDd° Wa Philip Ast,lith Weed.Parsons & Co. Albany, NY. ~ * eee 685 wit a it & i see ant en Sin | wt Ba § ait git Bie Ul Fig. 1 Fig. ta. Fig. 2 Fig. 2¢ Fig. 3 Fig. 32 Fig. 4. Fig. 4a Fig. 5 Fig. 5¢ Fig. 13 Fig. 13a. Fig. 11. Figs. 12, Fig. to. Fig. 10a. Fig. 6, Fig. 6a Fig. 7 Fig. 7a Fig. 8 Fig. 8a. PLATE VII WHITFIELDIA MARIA, Hall Page 73 rs - An embryo measuring .75X.75 mm.; without deltidial plates. Outline profile of the same. . A later stage of growth, at which the shell measures 5X5 mm., and the deltidial plates have de- veloped sufficiently to give the foramen a circular outline. . Outline profile of the same. . Dorsal view of a normal, mature shell. . Profile of the same. (28th Ann. Rept. N. Y. State Mus. Nat. Hist., pl. 25, figs. 9, 12.) MERISTELLA RECTIROSTRA, Hall Page 67 . The cardinal features at an extremely early stage of growth, the shell measuring 3X2 mm.; show- ing the broad, triangular foraminal opening and its faintly thickened margins. . Outline profile of the same. e . The same features when the shell has attained a size of 4.53.5 mm.; showing the gradual approximation of the sides of foramen and the narrowing of the umbo, without the formation _ of deltidial odikedoattihakal dt TO VOITANVAIIZG . The same features at maturity. Outline profile of the same. Dorsal view of a young individual. 12a, 124. Dorsal, profile, and ventral views of an adult specimen. (11th Ann, Rept. Geol. Surv. - Ind., pl. 27, figs. 13, 10-12.) MERISTINA NITIDA, Hall Page 70 Dorsal view of the youngest individual observed, having a size of 2.51.75 mm. Outline profile of the same. . Cardinal features of a shell having dimensions of 3X2 mm. . Outline profile of the same. - The same features in an individual having a size of 6X4 mm. In this example the umbo is abnormally elongate, giving an unusual prominence to the deltidial plates. . Outline profile of the same. ; . The same features at a size of 5X4 mm.; showing the total concealment, from incurvature, of the deltidial plates. Outline profile of the same. Figs. 9, 9, 94. Dorsal, ventral and profile views of the normal adult. (28th Ann. Rept. N. Y. State Mus. Nat. Hist., pl. 25, figs. 3, 4, 5.) , BRACEIOPODA. MEM.N.Y. STATE MUs. * : ‘ PLATEVTI.. a UU @0@ At” va Weed,Parsons & Co. Albany, NY. Philip Ast, lth “ ieee “Sag Lia ¥ AN Aue qty 0D 7g suosze J’peam 29999 9VVVDOVVDOD YY YK vor 0 HVOUY GY VY W v7 7 \ / } } YZ RAN Att" r NY)! |, Me WJ . ; r ¢ Yn BS ZN QW oe se Se Se & ee. a, SS, WIA SLILW Tet SAM SLviLs A’N'Wwarn “Ww ClLOGOlt Esto 2 Ss. a 7 “i = i re a = ‘er , a ’ PRESS OF WEED, PARSONS & CO., ALBANY, N Caras 3 oS ae —t . a. te Bet: ~ SP oe pew ea rapists ans) Glare. ~ hai ee a he eee ey i 4 ay Pudes «sy aes oe tine ae oH Gee ~~ #y a gpa tg Se rae ‘4 i Oe a oe - ~~ * rn et im were My | - ~ penile ne ahh etter gic : re ee ae - de * 1 a ni ot po ara neptin alg gett Sexe wt ere Se ee ie ae ee -. weak —— Se > act Cee d . ~~ P an aici sy = > r i ~ 7 i | < hae a 1 . 7 ae » < - = ou — - ™ _ rs 3 o, iy 2 ss ¢ o - oa . ’ : 4 ¥ “7 by nied “9 Pe = "ere “ ee oe ~ * 1%, x . = "a0 ae - _— ~ ” - rte a ey a + Gen” Mwy ade — - i : - eaeaicare @ ~ ~ 2 ore ad! —— oH na wx oe ame * hm re r - when a -_ Ant a wt — tes x hee ’ ~ . 7 — aa Be - oo. wliy the —NS | ry = —) a ‘ —- hit hy +) ‘omy? - r yi - mney) og ork mm. ° - & ja Te ~ sae | preiee « a ee “— = - w _ re ve * + em » ’ o ery ae al - . i- -