■* 1^ IU_- TZ o a C\J R ^ — CM p i — T— CO t^ — T— CO 1.. I Illinois State Geological Survey EDWARD M. !'"i T;i. :, VICTORIA MEMORIAL MUSEUM' QfTAWA, ^ GANAeA, STATE OF ILLINOIS STATE GEOLOGICAL SURVEY FRANK W. DeWOLF, Director Monograph 1 The MississippiAN Brachiopoda OF THE Mississippi Valley Basin i;v. \i Text BY STUART WELLER ILLINOIS STATE GEOLOGICAL SURVEY UNIVERSITY OF ILLINOIS URBANA 1914 Jeffersons Printing Company Springfield, III. ERINDALE COLLEGE LI3RARV —^ r - « • t ), I 'r)ME r- ■ »— L!. REPORT PUBLISHED UNDER STATE GEOLOGICAL COMMISSION Edward F. Dunne, Chairman Governor of Illinois Thomas C. Chamberlin, Vice-Chairman Edmund J. James, Secretary President of the University of Illinois Frank W. DeWolf, Director REPORT PREPARED UNDER STATE GEOLOGICAL COMMISSION Charles S. Deneen, Chairman Governor of Illinois Thomas C. Chamberlin, Vice-Chairman Edmund J. James, Secretary President of the University of Illinois CONTENTS PidE Preface 9 Geological introduction 12 Descriptions of genera and species 31 Lingula 33 Glossina 37 Orbiculoidea 39 Crania 43 Leptsena 48 Schuchertella 53 Sehellwienella 59 Streptorhynchus 68 Orthotetes 74 Chonetes 78 Chonopectus 95 Productella 97 Productus 103 Diaphragmus 135 Echinoconchus 138 Strophalosia 143 Rhlpidomella 147 Schizophoria 161 Camarophoria 169 Camarotcechia 175 Liorhynchus 185 Paryphorhynchus 187 Pugnoides 192 Allorhynchus 197 Pugnax 202 Rhynchotetra 205 Tetracamera 212 Shumardella 221 Rhynchopora 227 Centronella 241 Selenella 243 Trigeria 245 Centronelloidea 246 Cranaena 248 Dielasmoides 253 Dielasma 256 Girtyella 271 Dielasmella 279 CONTENTS Page Hamburgla 282 Atrypa 284 Cyrtina 286 Spirit erina 291 Delthyris 300 Spirifer 307 Brachythyris 370 Cyrtia 382 Syringothyrjs 384 Pseudosyrinx 404 Spiriferella 412 Acanthospira 418 Martinia 420 Amboccelia 423 Reticularia 427 Ptychospira 435 Eumetria 437 Acambona 448 Hustedia 451 Nucleospira 453 Camarophorella 458 Rowley ella 462 Athyris 464 Cliothyridina 472 Composita 484 LETTER OF TRANSMITTAL State Geological Survey University of Illinois, February 15, 1913. Governor E. F. Dunne, Chairman, and Members of the Geological Survey Commission : Gentlemen : When the present Survey was created in 1905 the Geolog- ical Commission adopted a balanced program which emphasized economic work of immediate, though perhaps temporary, value; it nevertheless included deep scientific research into fundamental problems, having only indirect bearing on economic geology of the State. The Survey has now published nineteen bulletins and many useful maps which have served an increasing public demand. Nine other reports are in manuscript form for early printing. I now have the pleasure of trans- mitting to you an illustrated report on the Mississippian Brachiopoda, by Professor Stuart Weller of the University of Chicago, and I recommend that it be published as the first of the scientific monographs of the Survey. Because of the highly technical character of this report it is perhaps fitting to state that an understanding of our geological formations is based not only on their materials but also on their included fossil remains, which indicate the relative time-periods during which the rocks were deposited. The Mississippian formations have their type localities in Illinois and the immediately adjoining states of the Mississippi Valley. The study of these strata for more than half a century has been attended by considerable confusion. Professor "Weller 's work, extending over a period of eight years, has solved many of the difficulties of stratigraphy and paleontology. His monograph will be gratefully received by profes- sional geologists throughout the world. Very respectfully, Frank W. DeWolf, Director. PREFACE No comprehensive study of the fossils of the Mississippian formations of Illinois and the adjacent parts of the Mississippi Valley Basin has ever been attempted. The species have been described in various publications, in state reports, in short papers in the transactions of learned societies, geological journals, etc.; many forms have never been illustrated, and many still remain undescribed. The literature on the subject is widely scattered, and most of it is not readily accessible to a large number of geological workers and students. James Hall's Report on the Paleontol- ogy of Iowa, published in 1858 and long since out of print, still remains the principal source of information to most students, concerning these faunas. The present work is a start towards the preparation of a series of monographs which it is hoped may eventually cover all the groups of organisms whose fossil remains are preserved in these formations. The brachiopods have been selected as the first group to receive consideration because of their almost universal presence in the faunas, and because their characters are such as to make them most readily recognizable under ordinary conditions. The specimens are much more apt to be preserved in a sufficiently complete condition to allow of their identification, than are the specimens of some other groups, such as the crinoids for instance. They are much more abundant than are the species of the several classes of Mollusca, and they do not require the grinding of thin sections, as do many of the Bryozoa. Furthermore the species are almost all rather closely limited in their geological range, being characteristic for the most part, of the fauna in which they occur. The field geologist who has the means at hand to enable him to recognize the brachiopods will not have difficulty in determining the horizon of the strata he may be studying. In the present work all the brachiopods known to occur in the forma- tions of the standard Mississippian section of the Mississippi Valley, so far as they could be secured, have been considered. These formations have their typical development not alone in Illinois, but also in Missouri and Iowa, so that not a few of the examples studied, described, and illus- trated are from localities outside of Illinois, although most of the species iriay be looked for in the Illinois formations. A few forms from adjacent regions, Indiana, Kentucky, Arkansas, and southwestern Missouri have been included in the discussion of the species and perhaps may never be found in any Illinois locality ; the reason for their inclusion here being their relationship to Illinois species. 10 MISSISSIPPIAN BRACHIOPODA Under the discussion of each species the name of the geological forma- tion or formations of whose fauna the species is a member, has been recorded, but no attempt has been made to record all the localities from which the species is known. In the explanation of the plates, however, the exact locality of the specimen illustrated has always been mentioned. The material used in the preparation of the report has been drawn from all available sources. The collections in the Walker Museum of The Uni- versity of Chicago have been a most prolific source of supply because of the presence of the Gurley collection and the James Hall collection, both of which are rich in types of Mississippian fossils, as well as of several smaller collections, of which the Sampson collection and the Van Home collection especially have supplied important specimens. Through the kindness of Dr. A. R. Crook, curator of the Illinois State IMixseum of Nat- ural History, several type specimens have been loaned for study and illus- tration from the collections of that institution. Dr. E. O. Hovey of the American Museum of Natural History in New York City has been most generous in his willingness to send many important type specimens to the author for study and illustration. The many types of species described by Winchell and by White and Whitfield, preserved in the White collec- tion in the museum of the University of Michigan, have been made avail- able for study and illustration through the co-operation of Dr. E. C. Case. Dr. R. S. Bassler has generously loaned certain material from the U. S. National ^luseum in Washington. Besides these curators of great public collections, private collectors have not been backward in furthering the preparation of the report. Prof. R. R. Rowley, of Louisiana, Missouri, who has described many species of Mississippian brachiopods, has gener- ously placed in the hands of the writer either the types or authentic speci- mens of all his species, which have been used for the illu.strations and as the basis for the definitions here published. Mr. D. K. Greger of Fulton. Missouri, has made his extensive collection of Mississippian brachiopods freely available to the writer in the preparation of the report. To all these curators and collectors I wish to express my great obligation, for without their co-operation the report could never have been made as com- plete as it now is. No claim of absolute completeness can be made for any work of this sort. Many species were described entirely without illustrations by earlier workers in the sub.ject, and in many instances the original types of these species have been lost or destroyed. It has been possible to recog- nize many such species from the definitions or from the definitions along with specimens more recently collected in the original localities, but there still remains a considerable number of such species which have not been recognized, some or all of which may still be cleared up through future collection and study. It is also to be expected that further work in the field may bring to light additional undescribed species. PREFACE 11 In the preparation of the body of the report new definitions of all of the species have been written so that the usage of terms is uniform through- out. In the definitions, the usual size of the members of 'any species has been expressed in the relative terms large, small, etc., these terms being used on the arbitrary basis that a specimen having a diameter of about 25 mm. or 1 inch, is medium sized. Specimens smaller than this are below medium size or small, while specimens of larger dimensions are above medium size or large. Besides these general dimensions, accurate meas- urements of one or more specimens have always been given. The usage of the terms cast and mould i.s not entirely uniform among paleontologieal writers. In the present work the term internal cast, or cast of the in- terior of the shell, is applied to the hardened matrix which has filled the interior of the shell or valve, the cavity of the shell or valve being as- sumed to be the mould in which such a cast was formed. All the illustrations on the accompanying plates are reproduced from photographs taken from the actual specimens. During the earlier part of the work I was materially assisted in the preparation of photographs by Mr. J. M. Jessup, and I wish here to acknowledge his very efficient aid in this part of the work. Stuart Weller. Chicago, September 1, 1913. GEOLOGICAL INTRODUCTION The Mississippian section in Illinois and the adjacent portions of the Mississippi Valley Basin constitutes the typical section of that system of strata in America. The entire series of formations is prevailingly cal- careous from its base to above the middle, but the upper portion includes conspicuous sandstone strata interbedded with important shales and lime- stones. The name " Subearbonif erous limestone" was first used by Owen for this series of formations and was the common designation for these rocks until 1891, at which time Williams^ proposed to subdivide the Car- boniferous into the Mississippian and the Pennsylvanian, the former name being applied to the so-called Subcarboniferous rocks of earlier authors, and the latter to the series of formation which had previously been desig- nated as Coal Measures. These two names were at once generally adopted by American geologists. The subdivision of the entire Mississippian system, with the application of geographic formation names to the several units, in accordance with modern usage, was first accomplished by James Hall in his Iowa Report- in 1858, although formation names, mostly of lithological or paleontologi- cal derivation, had been applied to the several formations by earlier aiithors. In his study of the section Hall had as an assistant Mr. A. H. Worthen, who later became the state geologist of Illinois, and who used Hall's nomenclature, with some minor changes, in his reports on the geology and paleontology of Illinois. These names, used by Hall and by Worthen, have become standard in the typical Mississippian section, al- though later, more detailed and more critical studies have necessitated certain important changes in the interpretation of the section, and the introduction of additional formation names. Future studies may necessi- tate other changes in the classification and nomenclature of the beds. The classification of the Mississippian system here recognized is as follows : CLASSIFICATION OF THE MISSISSIPPIAN SYSTEM V. Chester group. Clore formation. Palestine formation. IVIenard formation. Okaw formation. Rum a formation. Paint Creek formation. IBull. U. S. Geo). Survey No. 80. (1891.) 2 Report on the Geological Survey of the State of Iowa, vol. 1, Pts. 1 and 2. (1858.) GEOLOGICAL INTRODUCTION 13 Yankeetown foniiation. Renault forniatioa. Brewerville saudstone. IV. Ste. Genevieve limestone. III. Meramec group. St. Louis limestone. Salem limestone. II. Osage group. Warsaw fonnation. Keokuk limestone. Burlington limestone. I. Kinderhook group. Containing many formations more or less local in their geographical distribution. I. KINDERHOOK GROUP The lowermost formations of Mississippian age, constituting the Kinder- hook group, were correlated by Hall with the Chemung formation of the New York Devonian section, but they are now universally considered to be of younger age, and to constitute the initial group of formations in the JMississippian system. The Kinderhook formations are exceedingly variable in their development in different parts of the Mississippi Basin, including limestone, sandstone, and shale formations. The sections lack uniformity in any two localities separated by a considerable distance ; and the faunas show much variation in the several formations and in different regions. At the locality from which the name of the group was derived, Kinder- hook, Pike County, Illinois, the following section may be seen : SECTION AT KINDERHOOK, ILLINOIS Osage group. 4. 'Burlington limestone. Kinderhook group. Feet 3. Thin-bedded, fine-grained limestone 6 2. Thin-bedded sandstone and sandy shales 36 1. Argillaceous and sandy shale.s, partly hidden 40 Another locality considered as typical by Meek and Worthen, who first used the name Kinderhook group, is that exposed in the neighborhood of Burlington, Iowa, where the following succession of beds may be studied : SECTION AT BURLINGTON, IOWA Osage group. 8. Burlington limestone. Kinderhook group. Feet 7. Soft, butf, dolomitic limestone. .' ' 3-5 6. White, oolitic limestone 2-4 5. Fine-grained, yellow sandstone. 6-7 14 MISSISSIPPIAN BKACHIOPODA Feet 4. Compact, much-fractured, gray limestone 12-18 3. Thin band of hard, impure limestone, filled with Chonetes, often associated with a thin oolitic band 1/4-1 2. Soft, friable, arf>illaceous sandstone, usually yellow, but locally harder and bluish, with a large fauna of which Chonopectus fischeri is the most conspicuous species. The Chonopectus sandstone 25 1. Soft, blue, argillaceous shale (exposed) 60 At Hannibal, Louisiana, and Clarksville, Missouri, the section is as fol- lows: SECTIONS AT MISSOURI LOCALITIES Osage group. 4. Burlington limestone. Kinderhook group. Feet 3. Fine-grained, compact, buff limestone 10-15 2. "Vermicular sandstone and shale" (Hannibal sandstone) 70 1. Compact, blue-gray limestone with lithographic texture (Louisiana limestone) 60 At Hamburg, Calhoun County, Illinois, the section is similar to that at Louisiana, Missouri, except in the notable reduction in thickness of the Louisiana limestone, and the introduction of an oolitic limestone above the Louisiana. The section is as follows : SECTION AT HAMBURG, ILLINOIS Osage group. 5. Burlington limestone. Kinderhook group. Feet 4. "Vermicular sandstone and shale" (Hannibal sandstone and shale) (?) 3. White to yellow or flesh-colored oolitic limiestone, with in- terbedded layers of sandy shales (Hamburg oolite) . . . 1-15 2. Brown, sandy shale 1-8 1. Compact, gray limestone with lithographic texture (Louisiana limestone) 5 In central Missouri the entire Kinderhook is represented in the Chou- teau limestone, about 100 feet in thickness. In southwestern Missouri the Kinderhook section is made up of three members, as follows : SECTION IN SOUTHWESTERN MISSOURI Osage group. 4. Burlington limestone. Kinderhook group. Feet 3. Buff-colored limestone (Pierson limestone) 30 GEOLOGICAL INTRODUCTION 15 Feet 2. "Vermicular" sandstone with accompanying shales (Northview sandstone), about 60 1. Tough, bluish-gray, granular limestone (Chouteau lime- stone, lower part), about 20 In JefiEerson County, Missouri, 25 miles below St. Louis, the Kinderhook section is as follows : SECTION IN JEFFERSON COUNTY, MISSOURI Osage group. 5. Burlington limestone. Kinderhook group. Feet 4. Red to green, cherty limestone, often very argillaceous, (Fern Glen formation) 30 3. Fine-grained, yellow or brown sandstone (Bushberg sand- stone) 14 2. Sandy shale Ks 1. Gray or yellowish oolitic limestone (Glen Park limestone), about 1 In Union County, Illinois, in the W. i/o sec. 11, T. 12 S., R. 2 W., about 31/^ miles northwest of Jonesboro, along the creek west of the M. & 0. Railroad track, the Kinderhook has a very different expression from that at any of the points further north, as follows : SECTION 31'2 MILES NORTHWEST OF JONE.SBORO, ILLINOIS. Osage group. 4. Burlington limestone. Kinderhook group. Feet 3. Green, brittle shale 40 2. Iniipure, nodular limestone ( ?Rockford limestone) 1 Devonian. 1. Thinly laminated, black, brittle, shale, (Chattanooga shale) . . These sections will suifiee to exhibit the variable character of the Kin- derhook sediments. Some of the formations, as noted above, have already been given local formation names, and others will doubtless be named in the future, but in no case can any formational unit be traced continuously throughout the entire basin. In the central portion of the basin the Kin- derhook sediments invariably rest unconformably upon subjacent strata, but in the more northern region, as at Burlington, Iowa, and in the more southern region, as in Union County, Illinois, it is not improbable that the sedimentation Avas continuous from the preceding Upper Devonian into the Kinderhook. It is believed that in early Kinderhook time two distinct basins in the Mississippi Valley were occupied by the sea, one to the north and another to the south of a land barrier, because the faunas of these 16 MISSISSIPPIAN BRiVCHIOPODA two basins are fundamentally diiferent in composition and origin. With the progress of Kinderhook time this land barrier was gradually sub- merged, causing the borders of the seas upon the two sides to approach each other, until in late Kinderhook time the northern and southern seas joined, and the fauna from the southern sea spread into the northern basin, supplanting the pi-eviously existing fauna of that region. II. OSAGE GROUP The formations constituting the Osage group are very different from those of the Kinderhook in that they are fairly uniform in both lithologieal and faunal character, and can be traced through the entire Mississippi Basin. The formations commonly included in the Osage are the 'Burling- ton limestone, the Keokuk limestone, and the "Warsaw formation. Ulrieh,^ however, includes the last of these formations in the superjacent Meramec group, and considers the Fern Glen formation, here placed in the Kinder- hook, as a basal member of the Osage. Burlington limestone. — The Burlington limestone takes its name from Burlington, Iowa, and the formation has its most typical development in the southeastern counties of Iowa and the adjacent portions of Illinois. Further south the formation is continuously exposed in the Mississippi River bluffs from Quincy to northern Calhoun County, and also in south- ern Jersey County. It has a considerable area of outcrop in the river bluffs and elsewhere in Monroe County, and still further south in Jackson and Union counties. In its typical development in southeastern Iowa, a total thickness of about 150 feet has been recorded for the formation,^ but its thickness commonly falls short of this and in some localities is not over 100 feet. The formation is constituted mainly of limestone and chert in varying proportions. The limestone layers are conspicuously crinoidal, generally consisting of a mass of the separated column joints and plates, and are in many places remarkably pure, locally containing 98 per cent of calcium carbonate. In Iowa the uppermost 30 feet comprise the so- called Montrose chert bed, in which the limestone and chert occur in alternate horizontal bands a few inches in thickness, the chert constituting 50 per cent or more of the total mass. Elsewhere in the formation in this region the chert is less conspicuously developed, being present in oc- casional horizontal bands or in horizontal series of concretionary nodules. Further south the chert is not so conspicuously concentrated in the upper portion of the formation, but in many places occurs abundantly through- out the entire thickness, or elsewhere more concentrated near the base. lU. S. Geol. Survey, Prof. Paper, 36, p. 24 (1905); Bull. Geol. Soc. America, vol. 22, plate 29. (1911.) 2 Iowa Geol. Survey, vol. Ill, plate 28, opposite p. 330. (1895.) GEOLOGICAL INTRODUCTION 17 In the Monroe County exposures, the entire thickness of the formation is made up largely of alternating thin bands of chert and limestone, the chert constituting from 50 to 80 per cent of the total mass. In Union County, the formation is more cherty below and contains thick beds of pure limestone above. The fauna of the upper beds of the Burlington limestone is remarkably uniform throughout the entire extent of the formation, and consists largely of crinoids and brachiopods. The same species occur from Iowa to southern Illinois, and to central and southwestern Missouri. The faunas of the lower beds are more diverse in character, and in many localities contain species with Kinderhook affinities. Keokuk limcstorif.—T'he Keokuk lime.stone succeeds the Burlington with perfect conformity in those sections where both formations are present, and in places it is difficult to draw a sharp line of separation. In the neighborhood of Keokuk, Iowa, where the formation is typically devel- oped, it is about 75 feet thick, a measurement which perhaps is not ex- ceeded elsewhere. The limestone beds of the formation are in many places more or less argillaceous and are separated by shaly layers which commonly become more and moi-e conspicuous above, and locally, as in Monroe County, Illinois, constitute the major portion of the entire forma- tion. These limestone beds are prevailingly bluish, Avhile those of the Burlington are nearly white, or towards the base locally brownish, and the chert associated with the Keokuk limestone is darker than that which is commonly present in the Burlington. The fauna of the Keokuk, like that of the Burlington, is largely made up of crinoids and brachiopods, but in addition to these there are many bryozoans in the shaly beds, and some horn corals. South of St. Louis, especially in Monroe and Randolph counties, Illinois, a limestone stratum near the very top of the formation is made up of a crowded mass of the shells of the large Froductus magmis. A few feet above this Productus layer is another limestone bed just as conspicuously filled with the shells of a species of Spirifer. These two beds, in places quite separate, and elsewhere combined in a single layer, mark the upper limit of the Keokuk formation over a considerable area in southwestern Illinois and the adjacent portion of Missouri. Wlarsaw formation. — The Warsaw formation is typically developed at Warsaw, Illinois, where it attains a thickness of approximately 40 feet,' the section at that locality being as follows: 1 Bull. Illinois State Geol. Survey, No. 8, p. 84 (1907). 18 MISSISSIPPIAN BBACinOPODA SECTION AT WARSAW, ILLINOIS St. Louis limestone. Feet 11. Dense, bluish, breceiated limestone 10 Salem limestone. 10. More or less cross-bedded limestone, yellow on weathered surfaces and granular in appearance, containing large numbers of broken bryozoans; locally replaced by a calcareous grit or sandstone 8 Warsaw formation. 9. Thin-bedded bluish limestone, interbedded with cal- careous shales. Fossil bryozoans abundant, especially Lioclema punctaia and Archimedes wortheni 18 8. Fine blue shale 3 7. Hard, light-colored limestone, with few poorly pre.served fossils 4 6. Fine blue shale 8 5. Magnesian limestone with shaly bands. Fossils poorly preserved and as a rule rare, mostly bryozoans 8 Keokuk limestone. 4. Bluish shales with numerous geodes which are generally smaller than those in the magnesian limestone beds below 21 3. Magnesian limestone with chert bands 3 2. Magnesian limestone with numerous geodes. Some beds more or le.ss shaly. Geodes more numerous in the middle part of the bed. Fossils poorly preserved and rather rare, mostly imperfect bryozoans 15 1. Blue or gray crystalline limestone with many fossils. Thickness not known, the bed extending below river level (exposed ) 15 The dominant characteristic of the Warsaw formation is the presence of bluish shale with subordinate beds of limestone, but because of the softness of the beds they are rarely well exposed at the surface. The geographical distribution of the formation follows that of the Keokuk limestone wherever the full thickness of that formation is present north of the latitude of St. Louis. The formation is well developed in the Meramec basin in the St. Louis quadrangle, but southward it is seemingly absent, allowing the superjacent Salem or Spergen limestone to rest directly upon the Keokuk formation. For example, in Monroe County, Illinois, almost the entire Keokuk formation is represeuted by shales, with subordinate bands of limestone, which closely simulate the Warsaw, but the upper limit of these beds is marked by a conspicuous limestone layer from one to several feet in thickness, which is crowded with speci- mens of a species of Spirifer. In the Meramec Highlands section in the St. Louis quadrangle, this same Spirifer bed occurs about 50 feet below the base of the Salem limestone. These intervening Warsaw beds are wanting in the Monroe County section. GEOLOGICAL INTRODUCTION 19 In his classification of the Mississippian, Ulrica has included the Warsaw with the succeeding Salem or Spergen and St. Louis limestones in the Meramee group. This grouping of the formations is not followed here because the relationship of the Warsaw is manifestly closer with the subjacent than with the superjacent formations. Lithologically there is no satisfactory basis for differentiating the Warsaw from the subjacent Keokuk, and the faunal relations of the two formations are very close. In the typical expression of the two formations the Keokuk is essentially limestone with subordinate shale beds, while the Warsaw is largely shale with subordinate limestone beds; the transition from one formation to the other being gradual, with no suggestion of an unconformity. The fauna of the Warsaw does contain an element which is closely allied to the faunas of the superjacent formation, but this fauna is notoriously a recurrent element in our Mississippian series, occurring also well down in the Keokuk, in the St. Louis quadrangle and elsewhere.^ The absence of the Warsaw formation south of St. Louis and the contact of the Salem on the Keokuk, indicates a line of unconformity which is worthy of recog- nition as a line of major subdivision in the Mississippian series. Uncon- formable relations between the thin northern extension of the Salem and the subjacent Warsaw are also indicated at Warsaw, Illinois.^ III. MERAMEC GROUP The Meramee group was established by Ulrich^ to include the Warsaw, "Spergen" and St. Louis formations, but in the present report it is used to include the "Spergen" or Salem, and the St. Louis limestones, the Wai-saw formation being excluded and incorporated in the Osage group for reasons which have already been discussed. In the older reports of the Illinois Survey, by Worthen, this series of limestones was commonly called the St. Louis group, but this name, although proposed many years before the one here used, is inadvisable because the use of the same name for a subordinate formation and for the group leads to much confusion and therefore is not good practice. Salem limestone.*— The Salem lim^estone has its typical development in Indiana where it is the source of the well-known building stone which goes on the market as "Bedford Stone." The name Bedford limestone lU. S. Geol. Survey, Prof. Paper, No. 24, p. 90 (1904); U. S. Geol. Survey, Prof. Paper, No. 36, p. 24 (1905). 2 Bull. U. S. Geol. Survey, No. 438, pp. 21 and 40 (1911). 3 Bull. 111. State Geol. Survey, No. 8, pp. 83-88 (1908). 4 Spergen limestone of Ulrich. 20 MISSISSIPPIAN BBACHIOPODA has been used for the formation,^ but this name was also used much earlier and is still in use for a formation in Ohio, which prior use makes it unavailable for the formation here under consideration. In 1901 Cumings^ proposed the name Salem limestone for the formation, and in 1904 Ulrich* used the name Spergen in exactly the same manner. Cumings' name clearly has priority as a formation name, and by the application of the ' ' law of priority ' ' his name must be adopted and is consequently used here. This formation is represented in the section at Warsaw, Illinois, by a bed of limestone about 8 f6et in thickness. It increases to the south, and from Jersey to Randolph counties, its thickness is from 100 to 160 feet. The formation is limestone, almost entirely free from chert through- out, although the beds vary greatly in lithologic character. Some beds are very pure, white limestone, in many places containing great numbers of bryozoans ; some beds are oolitic, while others are decidedly dolomitie. Many years ago one of the magnesian beds was mined in Jersey and St. Clair counties for the manufacture of hydraulic cement. Towards the summit of the formation some of the beds assume lithologic characters resembling the superjacent St. Louis limestone, the transition from one formation to the other being gfadual, without a distinct stratigraphic break. The fauna of the Salem limestone has long been known as the Spergen Hill fauna, from which locality, in Indiana, it was long ago described by Hall and later beautifully illustrated by Whitfield. The fauna contains a large number of species, many of which are in many instances diminutive in form. Brachiopods and fenestelloid bryozoans are among the most conspicuous members of the fauna, in addition to which many gastropods- and pelecypods are locally present, besides some corals and other forms. St. Louis liinestoue. — The St. Louis formation has its typical develop- ment in St. Louis and in the Mississippi river bluffs to the north and south of that city. It is essentially limestone throughout, in some places quite free from chert, and in others with conspicuous chert beds, but nowhere represented by such extensive chert beds as are commonly present in the lower portion of the Osage group. The limestones of the formation are more or less heavy-bedded, and vary considerably in lithologic texture, but are rarely oolitic. A very characteristic phase is exhibited in beds of compact bluish-gray limestone, very brittle and breaking Avith a conch- oidal fracture, and generally exhibiting a texture almost like that of lithographic stone. In the bluffs north of Alton the formation contains 121st Ann. Rep. Dept. of Geol. and Natl. Resources, Indiana, pp. 291-427 (1897). 2 Jour. Geol., vol. 9, p. 232 (1901). 3U. S. Geol. Survey, Prof. Paper, No. 24, p. 90 (1904); Ma. Bureau Geol. and Mines, vol. 2, 2nd sen, p. 110 (1904). GEOLOGICAL INTRODUCTION 21 some important dolomitic beds in its lower portion, but such beds are much less conspicuous further south. A peculiar topographic feature marking much of the area which is immediately underlain by the St. Louis limestone, is the remarkable abundance of sink-holes; indeed in some portions of the State the boundaries of the formation can almost be draAvn by outlining the areas of sink-hole topography. The formation has a thickness of from 30 to 40 feet in southeastern Iowa; it increases in thickness to the south, attaining a thickness of some 250 feet in the river bluffs above Alton, and is said to be 325 feet thick in the St. Louis quadrangle.^ In Monroe and Randolph counties the thickness is not so great as that recorded in St. Louis. In southeastern Iowa the formation is largely a brecciated limestone, and in the bluffs above Alton, a similar brecciated bed about 20 feet in thickness is present near the middle of the formation. In the St. Louis quadrangle brecciated beds are present here and there at different horizons in the formation, but further south this feature has not been observed. The fauna of the St. Louis limestone is commonly not so large nor so well preserved as that of the Salem limestone, and in many places determinable fossils cannot be secured through considerable thicknesses of strata. The most varied faunas have usually been obtained from some of the cherty beds. A species of the bryozoan genus Cystodictya is one of the commonest fossils of the formation, and in many places occurs in great numbers upon some of the bedding planes. The corals of the genus Lithostrotion, L. canadensesind L. proliferum, are good index fos-sils. and where they occur they are as a rule present in abundance, locally almost entirely constituting beds a foot or more in thickness, but elsewhere, over considerable areas and through considerable thicknesses of strata, these corals may not be found at all. IV. STE. GENEVIEVE LIMESTONE Shumard^ first diflferentiated the strata immediately above the St. Louis limestone, and gave' to them a distinct formation name, the Ste. Genevieve limestone, although he failed to point out that the two forma- tions were separated by a distinct line of unconformity. This uncon- formity has been seen best in the Mississippi River bluffs below Ste. Genevieve, Missouri, where the actual contact of the formation upon the subjacent St. Louis liniestone may be observed at several localities, showing the uneven surface of the lower formation, and in places solution channels aloiig joint planes which have been filled with the younger formation. iBull. U. S. Geol. Survey, No. 438, p. 23 (1911). ^olJ^a^f- St. Louis Acad. Sci., vol. 1, p- 406 (1857); Mo. Geol. Surv., Rept. for 1855-1871, p. 293 (1873). 22 MISSISSIPPIAN BRACHIOPODA In Illinois the Ste. Genevieve limestone has a notable development in the valley of Fountain Creek and its tributaries in Monroe County, and extends northward as far as Alton, where it caps the Mississippi River bluffs. Wortheii included all of these beds in the upper portion of the St. Louis limestone. The name Ste. Genevieve ha.s been revived in recent years by Ulrich,^ in his study of the Mississippian section in western Kentucky, where he has recognized three members of the formation, the Fredonia oolite, the Rosiclare sandstone, and the Ohara limestone. This author's criterion for the recognition of the formation seems rather to be a lithologic suc- cession, limestone below and above with an intermediate sandstone, than any fauna! characteristics. In some localities the beds referred by him to the Ohara carry a characteristically Chester faunal assemblage, while at other points the Ohara fauna lacks these Chester characteristics and is distinctly older in general complexion. Because of this uncertainty as to the correctness of Ulrich's interpretation of the Ste. Genevieve, his subordinate member or formation names, Fredonia, Rosiclare and Ohara are not adopted in this place, although in certain sections in Mon- roe County, Illinois, there is a sandstone stratum with limestone both above and below it in the Ste. Genevieve. According to Ulricli the maximum thickness of his Ste. Genevieve in Kentucky is at least 245 feet, but the greatest measured section in Monroe County, Illinois, is about 75 feet, and it probably nowhere exceeds 100 feet. The thickness of the formation in its typical localities near Ste. Genevieve, Missouri, probably does not exceed that in Monroe County, Illinois. It is believed by the writer that some room for doubt exists as to the correctness of Ulrieh 's correlation of some of the beds in the extreme southern counties of Illinois which have been referred to the Ste. Geneveive limestone by him, and the description of the formation herein given applies only to its typical Mississippi Valley expression. The Ste. Genevieve includes certain remarkably cross-bedded lime- stones which are commonly more or less arenaceous ; some of the most conspicuously oolitic limestones in our entire Mississippian section ; and also some beds which are wholly arenaceous. In the bluffs at Alton about 48 feet of limestone and more or less arenaceous strata are referable to this formation. The thickness increases to the south, for about 75 feet was actually observed in Monroe County, and a maximum thickness of 100 feet may be present. In Monroe County, where the formation is best known by the writer, the basal portion comprises the remarkably cross- bedded, more or less arenaceous limestones above mentioned. On Andy's Creek, in this county, a conspicuous 12-foot sandstone stratum may be .seen lying about 20 feet above the lowermost observed beds of Ste. Gene- lU. S. Geol. Survey, Prof. Paper, No. 36, p. 39 (1905). GEOLOGICAL INTRODUCTION 23 vieve age iii the section, and below about 20 feet of limestone. This sandstone is very fine-grained, yellowish, and very cross-bedded. It re- sembles, in some respects, the Rosielare sandstone of Hardin County; and the section in which it occurs suggests the three-fold division of the Ste. Genevieve of that county, as described by Ulrich. In Monroe County, however, this bed does not appear to be a continuous formation, but only a local phase of the formation which has become wholly arenaceous. The fauna of the Ste. Genevieve limestone is in part a recurrent fauna from the Salem limestone, but associated with these recurrent forms are certain others which are characteristic of the Ste. Genevieve. The best index fossil of the formation is probably Pugnoides ottumwa, originally described from the Pella beds of Iowa, which are to be corre- lated with these Ste. Genevieve limestones. Another good index species, but leas common than the last, is Girtyella indiancnsis, which is also typical of the Pella beds of Iowa. V. CHESTER GROUP The name Chester Group was originally applied by Worth en to those strata of the Mississippian series typically exposed in Randolph County, from the base of the so-called "lower sandstone of the Chester group" to the summit of the Mississippian. The maximum thickness of this series of beds was estimated by Worthen to be at least 600 feet. A careful measurement of the Randolph County section by the writer gives a total thickness of about 550 feet, although a thickness of 743 feet is indicated in the Gilster well at Chester. The local details of the Chester section vary from place to place, but the larger features are persistent over wide areas. The lowermost sandstone has long been recognized as a distinct formational unit and was called Cypress sandstone by Henry Engelmann^ from certain extensive ex- posures on Cypress Creek in Johnson County. The series of beds super- jacent to the Cypress was called the Kaskaskia limestone by Hall. More recent field investigations have made it clear that the series must be subdivided, and Ulrich, in his Kentucky work,^ has defined two forma- tions, the lower of which he calls Tribune limestone and the upper, Birds- ville formation, which, together, constitute the Kaskaskia of Hall. How- ever well this classification may apply to this series of beds in Ken- tucky, it is inapplicable in the typical Illinois section, and it has been found necessary, in the course of recent field work, to establish an entirely new series of formational units for the Chester group. 1 Trans. St. Louis Acad. Scl., vol. 2, pp. 189-190 (1863). 2U. S. Geol. Survey, Prof. Paper, No. 36, pp. 55-66 (1905). 24 MISSISSIPPIAN BRACHIOPODA Brewerville formation.— The lower portion of the Chester group, as recognized by Worthen, and by Engelraann, is for the most part arenace- ous, and the name Cypress sandstone, as used by Engelmann, and later by lllrich, was originally applied to this lower sandstone member of the gioup.^ Recent field studiers have brought out the fact that two distinct formations are present in the Cypress, as it was originally defined, sep- arated by a distinct unconformity and overlap. The lower of these two formations is the Brewerville, and the upper, the Renault formation. The Brewerville sandstone is well-exposed in the Mississippi River bluffs in Brewerville and Prairie du Roeher townships, between Modoc and Prairie du Roeher, in Randolph County, where the thickness of the for- mation is about 80 feet. The formation consists of massive beds of fine-grained sandstone, which as a rule exhibit much cross-bedding. In its unweathered condition the sandstone is a light yellowish-brown, locally nearly white, but upon the exposed ledges it is more or less reddish-brown. It is the so-called "ferruginous sandstone" of some of the earlier writers upon the geology of the Mississippi Valley. Wherever the Brewerville has been critically studied by the writer, it is separated from the subjacent formations by a distinct erosion uncon- formity, and rests locally upon the Ste. Genevieve and elsewhere directly upon the St. Louis limestone. In much of this area a conspicuous basal breccia is present at the contact of the Brewerville with the St. Louis. No fossils have ever been recorded from the formation and none have ever been found by the writer. Renmdt formation. —The Renault formation has its typical development in the valley of Horse Creek and its tributaries in the eastern portion of Renault Township in Monroe County. It continues northward, where it is well developed east and northeast of Waterloo. To the south it is exposed in the Mississippi River bluffs below Modoc. The formation is exceedingly variable in its lithologic characters and includes sandstone, shale, and limestone members. Some of the sandstone members at or near the top of the Renault closely resemble the Brewerville, but they are com- monly thinner bedded and are associated M'ith arenaceous shales and with limestone lenses or more or less continuous strata of limestone. In many localities fossil tree trunks, lepidodendroids, are present in the sand- stones of this formation, while no fossils of any sort have been observed in the Brewerville. Northeast of Waterloo, a conspicuous bed of varie- gated red and blue or gray shale is a notable member of the formation, and other less important beds of similar variegated shales occur elsewhere 1 Engelmann also recognized certain beds of limestone and sandstone in Johnson County which he believed to be sub-Cypress in^ position, but no sub-Cypress Chester was ever recognized by Worthen in the typical Randolph County area. GEOLOGICAL INTRODUCTION 25 in it. The thickness of the Renault varies from 40 feet or less to a maxi- mum of 100 feet or more. The Renault formation commonly overlaps the subjacent Brewerville to the west and rests directly upon the St. Louis or Ste. Genevieve lime- stone in unconformable contact, and this unconformity is also present between the Renault and the Brewerville itself. On Hickman Creek, north- east of C!olumbia, the Renault rests upon the Ste. Genevieve with a con- spicuous basal conglomerate, and elsewhere in the same general region it rests upon the Brewerville with a basal conglomerate, mainly of limestone pebbles, but with some pebbles of crystalline rock. Eastward from the western margin of the Renault, away from the shore-line of the period, the limestone members of the formation become more and more con- spicuous. In some of the limestones and associated calcareous shales in the Renault, fossils are exceedingly abundant, the facies of the fauna being typically '"Chester." The bryozoan genus Archimedca, however, i^ as a rule sparsely represented in the faunas and is in many places wholly absent, although in at least one locality it has been observed in abundance. The jrenus Lxjropom, on the other hand, is in many localities exceedingly abundant. The crinoid fauna of these beds is the most varied and best preserved of any observed in the Chester group, Talarocinnus being one of the commonest genera of these organisms. Yankeetown /orm«fiOM.— Overlying the Renault formation is a thin but most persistent siliceous formation of peculiar lithologic character, locally quartzitic. Although this bed is entirely unfossiliferous, so far as it has been observed, it has served as a key formation in the interpretation of the Chester succession to a greater extent than any other fomiational unit. Some of its most typical exposures may be seen in the region adjacent to the Yankeetown school, about 6 miles southwest of R«d Bnd, from which locality the name of the formation has been derived, but it occurs as well in tlte extreme north of the area of the outcrop of the "Chester", on Hickman Creek, northeast of Columbia, and near Millstadt. It is also well exposed in the Mississippi River bluff section one and one-half miles below Modoc, and at many intervening localities. The thickness of the Yankeetown is probably nowhere over 20 feet, and commonly is le.ss. Its color is light, commonly gray or yellowi.sh, or in many localities nearly white. It is very irregularly, and more or less cross-bedded, having a decidedly knotty appearance, and locally is distinctly banded. It is commonly more or less arenaceous and in some localities certain beds are quartzitic. Where the formation is encountered in wells it appears to be a very hard, siliceous limestone, and in dug wells it usually puts an end to any further excavation. The Yankeetown is so hard and resistant that over considerable areas the superjacent beds were 26 MISSISSIPPIAN BRACIIIOPODA removed by erosion in pre-Pennsylvauian time, and in such areas this formation constitutes the floor upon which the Pennsylvanian beds have been deposited. There is reason to believe that the Yankeetown rests unconformably upon the subjacent Renault, since the immediately underlying strata are in some localities limestone, in others sandstone, and in still others shale. Padnt Creek formation— Above the Yankeetown formation is a series of strata approximating 60 feet in thickness, which are shales below, passing into limestones above. Near the base of this Paint Creek formation, either resting directly upon the Yankeetown or separated from it by a few feet of blue or gray shales with perhaps some thin calcareous beds, is a deep-red, clay member. Its summit is about 25 feet above the top of the Yankeetown chert in a tributary of Paint Creek about five and one-half miles northeast of Prairie du Rocher, from which locality the formation name has been taken. In fresh exposures this red bed exhibits little or no stratification; on being subjected to atmospheric agencies it first crumbles into small, angular fragments which eventually disintegrate into a fine, red mud. The appearance of the stratum is more that of a residual clay than anything else familiar to the writer. It is a constant member of the formation, being present throughout the entire extent of surface outcrop of this portion of the Chester group, and being recognized in deep-well records beyond this region. No fossils have been found in the red-clay member of the Paint Creek formation, but in the succeeding calcareous shales and limestones fossils are common in many localities. Like the faunas of the Renault, the Paint Creek faunas are typically Chester in facies and contain many of the species which have usually been reported from the "Chester" or "Kas- kaskia" limestone in the past. The genus Archimedes is more commonly present than in the Renault, although it is as a rule not abundant, as is commonly the case in some of the higher beds. Lyropora is also a com- mon form in some localities, and among the brachiopods Diaphragmus elegans abounds in many places. Rtmia formation. — Succeeding the upper limestone member of the Paint Creek is a shale formation, in which a thin sandy member is usually pres- ent near or a little above the middle. These beds are most typically ex- posed in some of the tributaries of Horse Creek northeast of Ruma, and attain a thickness of 25 to 40 feet. The shales are in pai-t variegated and in part blue or gray, this being, in fact, the highest conspicuous horizon of variegated shales in the Chester group. The shales have nowhere been observed to be fossiliferous, but in the sandstone member of the forma- tion, lepidodendroid tree trunks, probably identical with those in the Renault, occur in many localities. GEOLOGICAL INTRODUCTION 27 Okaw formation. — Succeeding the Ruina formation is an alternating series of limestones and shales attaining a thickness of about 200 feet. The shales of this Okaw formation are commonly blue or gray, rarely with a slight admixture of red and blue, which is such a conspicuous feature of some of the shale horizons lower in the section. The limestones vary greatly in texture, some being highly crystalline, some oolitic, and others rarely cherty. Their color is also variable from gray or blue to nearly white. At least four conspicuous limestone horizons are present in the Okaw, the highest of which is the quarry ledge at Menard in the South- ern Illinois Penitentiary prison yard. Both the shales and the limestones of the Okaw formation are com- monly fossiliferous, and in many localities abundantly so. Within the formation are several more or less distinct faunal zones, although the de- tails of the faunal distribution of the fossils has not yet been wholly worked out. At the base of the lowermost limestone member there is commonly present a zone, several feet in thickness, which is especially marked by the brachiopod genus Martinia, this being the only horizon from which members of this genus have been recognized. Associated with Martinia, in most localities, are great numbers of bases of the crinoid Agassizocriiius, along with other characteristic Chester forms. A few feet higher, still in the basal limestone member of the formation, wing-like plates from the ventral disk of Pterotocrinus depressus occur so abund- antly in many localities as to almost entirely coA'er some surfaces of the limestone, in fact these plates of several species of Pterotocrinus consti- tute a very notable element in the faunas of the lower members of the Okaw formation. Archimedes is especially abimdant in the faunas of the lower members of the formation, as well as a great variety of other bryozoans. Some 60 feet above the base of the formation occurs a very constant oolitic limestone member, 10 or more feet in thickness, with a fauna in which many small pelecypods and gastropods are present. The summit beds of the formation are usually calcareous shales with interbedded thin limestones, and locally a sandstone ledge 10 to 12 feet in thickness is present a few feet above the highest heavy ledge of limestone. These shaly, upper Okaw, beds are commonly abundantly fossiliferous, the large blastoid, Pentremites snicatus. so far as it has been observed by the writer, being restricted to this horizon. Another species which has been found in most localities where fossils have been col- lected from these higher beds, and which has been seen at no other horizon, is Archimedes laxus. The brachiopod species CamAirophoria expla.^iata is present in most of the Okaw faunas, and has been observed by the writer only rarely in any other Chester horizon. This formation has been the source of by far the 28 MISSISSIPPIAN BRACHIOPODA greater number of species which have been described by the various writers from the "Chester" of Illinois, and a full faunal list of the forma- tion would include nearly all of the Chester or Kaskaskia species in our literature. The various members of the Okaw formation are well exposed in the Mississippi River bluffs above and below the tributary Okaw or Kaskaskia valley, this valley being entirely excavated from the rocks of this forma- tion at its point of juncture with the valley of the Mississippi, hence the name here adopted for the formation. Menard formation. — The Menard is a conspicuous formation of lime- stone with interbedded shales, well exposed in the middle portion of the bluffs at Chester. One of its best exposures is immediately south- east of the hospital for criminal insane at i\Ienard. In its typical expres- sion, this formation is a thin and moderately thick-bedded limestone, the bedding planes being undulating and hummoeky in character, with thin, shaly partings. In places these shaly partings become thicker, and shale beds of as much as five feet or more in thickness are present. The basal portion of the formation, where it is exposed, is seen to be shale, as much as 35 feet of fine, blue, clay shale being present in some localities between the top of the Okaw and the typical limestone beds of the Menard. The lithologic character of the limestone of the formation differentiates the Menard rather sharply from most of the limestone strata of the Okaw. The limestones of the lower formation are commonly more or less crystalline or granular, often crinoidal, sometimes oolitic, and usually free from chert. In the Menard the limestones are nearly always close-textured, fine-grained rocks, and there may be a small amount of chert ; they are brittle, and often exhibit a conehoidal fracture. Because of the difference in texture, the weathered surfaces of the Menard are commonly smooth, those of the Okaw usually being more uneven. The color of freshly broken surfaces of the Menard is usually a bluish gray, while that of the Okaw limestone is commonly lighter, some beds being nearly white. Locally, there are crystalline strata in the Menard which closely resemble certain of the Okaw beds, but such strata are always of limited thickness and usually occur in the higher portion of the forma- tion. The thickness of the Menard is about 80 feet. It is well exposed in the Mississippi River bluffs from Chester to Rockwood, and the valley of Mary's River, at its mouth, is excavated entirely through this forma- tion into the higher beds of the Okaw. The fauna of the Menard is very different from that of the Okaw. One of the most conspicuous species is a large pelecypod of the genus Sulcatopinna. This is associated with several other species of pelecypods, nnd with the large, typical forms of Composiia suhquadrata and Spirifer in- crebescens. Pentremites and Archimedes are not conunon in the formation GEOLOGICAL INTKODUCTION 29 except locally in some of the uppermost beds, and but a single species of Pentremites, P. cherokeeiis Hall, has been collected. Palestine fm-maticn.— The formation succeedinj^ the Menard is arena- ceous throughout in most sections, consisting in part of heavy beds of sandstone suitable for building purposes, and in part of thinly bedded, ripple-marked sandstones or arenaceous shales. Locally, however, more argillaceoiis shales are well developed in the formation. The formation is present in the higher portion of the bluffs at Chester, and has been quarried at several points for building stone. The buildings of the peni- tentiary at Menard are constructed of this rock. The more sandy facies of the formation are exceedingly well exhibited along some of the tribu- taries of Tindall Creek, in Palestine Township of Randolph County. The thickness of the formation is about 75 feet, and it seems to lie with some degree of unconformity upon the subjacent Menard limestone. The only fossils which have been seen in the formation are fragments of Lepi- dodendron trunks. Clore formation. — The highest formation in the Chester Group in Randolph County, is a limestone immediately overlying the Palestine sandstone. The greatest thickness actuallj- measured is 30 feet, but it certainly exceeds this thickness in many localities. The transition beds from the underlying sandstone to the Clore limestone, consist of arena- ceous and calcareous shales, with some beds of limestone, occupying, in places, an interval of as much as 25 feet below the more continuous lime- stone strata. The lithologic characters of the limestone beds are vari- able, some being thin bedded and almost shaly. others being similar to the Menard in texture and hardness, but usually darker in color, while others are more granular or crystalline. Some shale beds are included in the formation. The Clore limestone caps the summits of the hills upon which the city of Chester is built, and it outcrops in the heads of several of the ravines adjacent to the town. The formation also caps some of the higher hills east and northeast of Chester until it passes beneath the over- lying Pennsylvanian. Typical exposures of it occur in the heads of the ravines along the southwest side of the high ridge, extending from Clore school to the Randolph County farm. The most extensive exposures which have come under observation are in Bremen Township of Randolph County, about two miles northeast of the village of Bremen, where a small anticlinal flexure causes its surface outcrops to spread out on either side of Little Mary's River. The fossils of the Clore limestone are locally more conspicuous than those of the Menard. Some of the shaly beds are filled with fossils and are suggestive of certain phases of the Okaw formation, but the asso- ciation of species is different. In those beds resembling the Menard in texture, some of the Menard species are commonly present. Descriptions of Genera and Species Class BRACHIOPODA Order ATREMATA Family LINGULIDJE Genus LINGULA Bruguiere Description.— Shell thin, linguiform or tongue-sliaped, subequivalvatC; elongate-ovate or subquadrate in outline. Brachial valve slightly shorter than the pedicle and with a slightly thickened hinge-line. The pedicle opening common to the two valves. Surface of the valves usually shining, smooth or marked by concentric or radiating striaa. Internally, the muscular impressions are numerous but usually indistinct. Remarks.— The genotype of Lingula is the recent species L. anatina, but from the state of our knowledge of the characters of the ancient species which have been referred to the genus, there seems to be reason for sepa- rating only a few of them generieally from the living forms. It is true that the internal characters, especially the arrangement of the muscular scars, are insufficiently known or wholly unknown in many of the species which have been described from Paleozoic faunas, and it is possible that with future increased knowledge of these characters other generic dif- ferentiations may be drawn. Ordinarily it is difficult or impossible to differentiate between the two valves of a fossil species of Lingula. LlNGUIA MEMBEANACEA Winchell Plate I, Fig. 5 1863. Lingula menibranacea Winchell, Proc. Acad. Nat. Sci. Phil., p. 3. 1900. Lingula memiranacea Weller, Trans. St. Louis Acad. Sci., vol. 10, p. 65, pi. 1, fig. 20. Description.— Shell ovate-subqviadrangular in outline, the greatest width towards the front, the valves very flat. Postero-lateral margins nearly straight as they approach the beak, where they meet in a very broadly obtuse angle, rounding into the lateral margins distally; lateral margins nearly straight or very gently convex, diverging slightly anteriorly ; the antero-lateral margins rounding into the truncated anterior margin. The beak depressed and inconspicuous, not quite reaching the posterior margin. Surface marked only by concentric lines of growth varying 34 MISSISSIPPIAN BRACHIOPODA someAvhat in strength and usually situated about one-half millimeter apart. The dimensions of the type specimen are : length, 12 mm. ; great- est width, 8 mm. ; width at postero-Iateral extremities, 6 mm. Remarks.— The holotype only of this species has been observed, an illus- tration of which is given on the accompanying plate. The specimen is a single valve, whether pedicle or brachial cannot be determined, lying upon a fragment of fine-grained, yellow sandstone. It is imperfect, being somewhat broken upon the margins, but seems to be sufficiently distinct from any of the other species recognized, and may be distinguished by its ovate-subquadrangular outline. The specimens from the Waverly for- mations of Ohio and Pennsylvania which have been identified with this species by Winchell, Meek, and Herrick, are all specifically different from this Iowa shell. Horizon.— ChonoYiectns sandstone of the Kinderhook. LiNGULA LOUISIANENSIS n. Sp. Pate I, Fig. 3 Description.— Shell small, much compressed, ovate-subquadrangular in outline, the lateral margins gently convex in the central portion, postero- laterally the curvature increases and passes into the somewhat narrowlj' rounded posterior margin, antero-laterally the curvature increases more abruptly than posteriorly, passing into the broadly rounded or sub- truncate anterior margin. The dimensions of a nearly complete valve are: length 9.7 mm., width 5.6 mm. Surface of the brachial ( ?) valve, in the internal cast, compressed along the postero-Iateral margins, the apex of the convex portion of the valve lying a little within the apex of the posterior margin, a slight nledian ridge, indicated by a depression in the surface of the internal impression, passes anteriorly from near the apex of the valve for nearly half its length. Surface of the valve nearly smooth, marked by fine, but somewhat irregular lines of growth, and by the faintest suggestion of radiating striae. Remarks. — The specimen from which the above description has been made is a nearly complete internal cast of what seems to be a brachial valve, with only fragments of the shell itself preserved. The external sur- face is not well preserved anywhere, all that can be seen being restricted to a few fragments of the shell still retained on the specimen. In size and general form the species resembles L. gorbyi from the Chouteau lime- stone, from which species it may be distinguished by reason of its sub- truncate anterior margin. Hon'soji.— Louisiana limestone of the Kinderhook. LINGULA 35 LiNGULA GORBYi Miller Plate I, Figs. 1, 2 1892. Li)U)ula gorhyi Miller, Adv. Sheets ISth Rep. Geol. Surv. lad., p 55, pi. 9, figs. 3, 4. 1894. Lincjxda gorhyi Miller, 18th Rep. Geol. Sui-v. Ind., p. 309, pi. 9, figs. 3-4. Description.— Shell small, siibelliptical in outline, the width more than one-half the length. The dimensions of a nearly complete valve are: length 11 mm., width 7.2 mm. Valves gentl}^ convex, the anterior margin subsemicircnlar, the lateral margins gently convex, the posterolateral margins nearly straight or gently convex and meeting at the beak in a rounded, obtuse angle. Surface marked by very fine, exceedingly regular. Concentric costa% from 12 to 15 of which occupy the space of 1 mm., and usually by rather ob- scure concentric undulations. Remarks. — This species may be recognized by its exceedingly regular con- centric COStffi. Horizon.— Chouteau limestone of the Kinderhook. LiNGxn^A HALLi White Plate I, Fig. 4 1862. lAngula Halli White, Proe. Boston Soc. Nat. Hist., vol. 9, p. 30. Description. — Shell very small, longitudinally subelliptical in outline, the length about twice the width, the greatest width a little in front of the middle ; the postero-lateral margins meeting at the beak in an acute angle, the lateral margins gently convex, the anterior margin narrowly rounded. The dimensions of the holotype are: length 6.1 mm., greatest width 2.8 mm., convexity of pedicle valve .8 mm. Pedicle valve rather strongly convex in proportion to the width, the greatest convexity posterior to the middle ; the beak, in the internal cast, rather abruptly constricted and produced posteriorly a little beyond the general margin of the valve. Surface marked by fine, concentric lines of growth, somewhat variable in strength. Brachial valve imperfectly preserved, its convexity evidently about equaling that of the pedicle valve. JKemarfcs.— The holotype of this species is an internal cast of what is probably the pedicle valve, preserved upon a fragment of white chert. The reverse of the same chert fragment preserves small portions of the shell substance of this valve and the incomplete brachial valve, someAvhat displaced, exhibiting the internal surface of its posterior portion. The species differs notably from any of the other recognized Lingulas in the faunas under consideration, in its narrowly subelliptical shell, approach- 36 MISSISSIPPIAN BRACHIOPODA ing in its outline L. spatulata of the Genesee shale of the New York Devon- ian. The species, however, is larger than the illustrated examples of L. spatulata, and is more narrowly rounded at the anterior margin, Homow.— Burlington limestone. LiNGXJLA vARSOVBENsis Worthen Plate I, Pig. 6 1884. Lingula varsoviensis Worthen, Bull. No. 2, 111. State LIus. Nat. Hist., p. 24. 1890. Lingula varsoviensis Worthen, Geol. Surv. 111., vol. 8, p. 104, pi. 11, fig. 8. Description.— 'SheW rather large for the genus, subovate in outline, the width about two-thirds the length, the greatest width anterior to the middle. The dimensions of the holotype are: length 21.8 mm., greatest width 14 mm. The valves moderately convex, the greatest depth posterior to the middle ; the anterior margin subsemicircular, the lateral margins gently convex, the posterior margin shorter than the anterior, the postero- lateral margins meeting at the beak in a broadly obtuse angle and round- ing somewhat abruptly into the lateral margins distally, the beak ap- parently not prominent. The surface marked by numerous, regular, crowded, concentric lines of growth which are somewhat variable in strength, becoming more crowded towards the margins ; the median one- fourth of the valve is marked by faint, radiating costae which are only noticeable anteriorly from the middle of the valve. 7?cmarA;s.— This species is one of the larger members of the genus in the faunas under consideration, being equalled in this respect only by L. indianensis. These two species are, indeed, closely allied and should perhaps be considered as synonymous, but owing to the limited number of specimens examined, the holotypes of the two species, it is not possible to certainly determine their identity. The type of L. indianensis is rela- tively a little broader, a character which may be due to the somewhat crushed condition of the specimen, the concentric markings of the two specimens are entirely similar in strength and expression, but the L. indianensis does not possess the faint radiating costae in the median portion of the valve which are present upon L. varsoviensis. For the present the two species will be considered as distinct, their separation being ba.sed upon the presence of the faint, radiating costffi in L. varsoviensis and their ab- sence in L. indianensis. More extensive collections may show that this character is not of sufficient value to be iised as a means of .separating the two forms specifically, in which case Worthen 's name L. varsoviensis v/ill be applicable to all of the specimens. fl'omow.— Warsaw beds. GLOSSINA 37 LiNGULA iNDiANENsis Miller and Gurley riate I, Fig. 7 1894. Lingula indiaiiensis Miller and Gurley, Bull. No. 3, 111. State Mus. Nat. Hist., p. 69, pi. 7, fig. 1. Description.— '^h&W rather large for the genus, subovate in outline, the length about one-half greater than the width, the greatest Avidth anterior to the middle. The dimensions of the type specimen are : length 21.8 mm., width 14.9 mm. Valves gently convex, the anterior margin subsemicircular, the lateral margins gently convex, the posterior extremity much narower than the anterior, the postero-lateral margins meeting at the beak in a very broadly obtuse angle and rounding rather abuptly into the lateral margins; the beak not prominent. Surface marked by fine concentric lines of growth towards the beak, which become coarser, more irregular and more or less undulatory towards the margins. Bemarfcs.— This species may be recognized by its subovate outline, its rather large size, and its more or less irregular concentric markings. It is most closely allied to L. varsoviensis, from which it can be distinguished only by the absence of fine radiating costae from the median portion of the valve. ffomoM.— Crawfordsville shale. Genus GLOSSINA Phillips Description. Shell thin, broadly ovate-subtrigonal in outline, acuminate posteriorly and rounded anteriorly. Surface of the shell usually shining as in Lingula, and marked by concentric lines of growth. The internal markings of the valves obscure and imperfectly known. Remarks.— This genus has been established to include a few linguloid species which differ from Lingula proper in the subtrigonal outline of the shell. The internal characters of the shell are not sufficiently well known to make it possible to determine whether or not the arrangement of the muscular scars corresponds with that of Lingula. Glossina sedauensis (Miller) Plate I, Fig. 11 1892. Li)ignla sedaliensis Miller, Adv. Sheets 18th Rep. Geol. Surv. Ind., p. 54, pi. 9, fig. 2. 1894. Lingula sedaliensis Miller, 18th Rep. Geol. Surv. Ind., p. 308, pi. 9. fig. 2. Description.— Shell triangularly subovate in outline, longer than wide, the greatest width towards the anterior margin. The approximate di- mensions of a large but very incomplete example are: length ±17 mm., width ±13 ram. 38 MISSISSIPPIAN BBACHIOPODA Valves depressed convex, the anterior margin broadly rounded, ap- proaching subcircular, passing gradually into the elongate, nearly straight postero-lateral margins, meeting in an acute angle at the beak, which is sometimes narrowly rounded. Surface marked by slender, raised, regular, concentric costse, with broad, flattened spaces between, about four or five occupying the space of one millimeter in the median portion of mature shells towards the front, becoming much crowded towards the postero-lateral margins. Eemarks. — This species may be easily recognized by its subtriangular form and by the style of its surface markings. Horizon. — ChonteaxL limestone. Glossina lineolata (R-owley) Plate I, Fig. 12 1908. Lingula lineolata Rowley, Mo. Bureau Geol. and Mines, vol. 8, 2nd ser., pp. 87 and 100, pi. 19, figs. 35-36 ; pi. 20, figs. 19-21. Description. — Shell small, compre.s.sed, broadly triangularly subovate in outline, the greatest width anterior to the middle. Anterior margin broadly rounded and passing regularly into the lateral margins, the postero-lateral margins long, gently convex, meeting at the beak, the angle being 90 degrees or less. The dimensions of one of the co-types are : length 8 mm., width 7.5 mm. Ventral (?) valve compressed, the greatest depth posterior to the mid- dle, the convex curvature of the surface more abrupt to the postero- lateral margins. Surface marked by strong, regular, sublamellose, con- centric markings. Eemarks. —This species was described by Rowley from two specimens which may possibly belong to two different species. The above description is based upon the smaller of the two cotypes. In its great relative width this specimen resembles the subtrigonai linguloid shells which have been placed in the genus Glossina, and by reason of that character alone the species is here included in that genus. The species differs from G. sedalietisis of the Chouteau limestone in its smaller size, its less acute beak, and in its more crowded and more sublamellose concentric markings. Homow.— Louisiana limestone. OEBICULOIDEA 39 Order NEOTREMATA Family DISCINID^ Genus ORBICVLOIDEA d'Orbigny Description. Shell subcircular or subelliptical in outline, inequivalvate. Pedicle valve nearly flat or depressed-convex, with the apex excentric and inclined slightly towards the posterior margin ; a pedicle groove originates at the apex of the valve, passes posteriorly for a short distance, beyond which point it is continued as a pedicle tube which pierces the substance of the valve very obliquely, opening to the interior near the posterior margin. Brachial valve depressed conical, with the apex ex- centric and inclined posteriorly. Surface of the valves smooth, or more commonly marked by concentric lines, and more rarely by fine radiating COStffi. Bemarks.—The species of this genus are most commonly represented by the subcorneal brachial valves, and it is from the form, proportions, and surface characters of these valves that most of the species have been differentiated. Specimens of the pedicle valves are less commonly pre- served, and when seen the course of the oblique pedicle opening can rarely be traced. Orbiculoidea cap ax (White) Plate I, Fig. 13 1862. Discina capax AVhite, Proc. Boston Soc. Nat. Hist., vol. 9, p. 30. WOO. Orbicvloidea capax Weller, Trans. St. Louis Acad. Sci., vol. 10, p. 65, pi. 1, fig. 19. Description.— Shell below medium size, subcircular in outline, length and breadth probably about equal. The dimensions of the holotype are : maximum diameter 22 mm., convexity of brachial valve approximately 5 mm. Pedicle valve not known. Brachial valve depressed conical, the apex excentric posteriorly and inclined towards the posterior margin, apparently situated about one- fourth or one-fifth the length of the valve from the posterior margin, the greatest convexity of the valve in front of the apex; the surface gently convex from the apex to the anterior margin, sloping more abruptly to the lateral margins, and a little concave to the posterior margin. The surface marked by fine, regular, concentric lines of growth, and by more or less obscure radiating lines. Remarks. — The holotype of this species, which is the only example seen, is a much crushed and imperfect brachial valve, the entire outline of which cannot be determined. The central portion of the valve, however, 40 MISSISSIPPIAN BRACmOPODA is well preserved, and in the preparation of the above description it has been assumed that the form and contour of the shell, as indicated by the growth lines of this central region, represents the outline of the entire shell. The species has been identified by Winchell from the Marshall and Waverly formations of Michigan and Ohio, but the specimens so identified are probably different from this Chonopeetus sandstone shell. Horizcn. —Chonopectus sandstone of the Kinderhook. Okbiculoidea sampsoni (Miller) Plate I, Pigs. 21, 22 1891. Discina sampsoni Miller, Adv. Sheets 17th Rep. Geol. Surv. Ind., p. 80, pi. 13, figs 10, 12. 1892. Discina sampsoni Miller, 17th Rep. Geol. Surv. Ind., p. 690, pi. 13, figs. 10, 12. Description.Shell small, suboval in outline, the length usually greater than the width. The dimensions of one of the type specimens, a brachial valve, are : length 12.5 mm., Avidth 12 mm., convexity 2.8 mm. Pedicle valve nearly flat, marked by regular, nearly equidistant, eon- centric lines, about four of which occupy the space of 1 mm. ; the pedicle opening excentric. Brachial valve conical, with the apex excentric posteriorly and in- clined posteriorly, its distance from the posterior margin being variable, the greatest depth of the valve usually slightly in front of the apex, the surface sloping with a gently convex curvature from the apex to the anterior and antero-lateral margins, becoming slightly concave to the postero-lateral and posterior margins, in some specimens with the beak situated more than usually posterior, the posterior slope is nearly vertical. Surface marked by fine, regular, concentric lines of growth which are somewhat variable in strength, and by exceedingly fine radiating lines which can be detected upon well-preserved specimens only, with a good lens. Internally, a slightly elevated and very narrow ridge extends anteriorly from the apex for about one-third the distance to the anterior margin, and in front of its anterior extremity is a transverse series of four, small, slightly elongated papilla'. Bemarks. — The muscular impressions on the interior of the brachial valve, represented by the slight median ridge and four papilla? mentioned above, have been observed in only one example, one of the co-types, where they appear as depressions in the surface of the internal cast where the test has been removed. Homon.— Chouteau limestone of the Kinderhook. ORBICULOIDEA 41 Orbiculoidea KEOKUK (Gurley) Plate I, Pigs. 14-17 1884. Discina Keokuk Gurley, New 'Carboniferous Foss., Bull. No. 2, p. 6. Descriptio7i.— Shell rather large for the genus, subeircular in outline. The dimensions of a pedicle valve, one of the cotypes, are: length 16.5 ram., width 18 mm. The width of a second cotype is 21 mm. Pedicle valve nearly flat, the pedicle opening excentric, its external surface marked by regular, sublamellose, concentric lines of growth. Brachial valve depressed conical, the apex situated at about one-fourth the length of the shell from the anterior margin, the surface apparently gently convex from the apex to the anterior and lateral margins and slightly concave to the posterior margin. The surface marked by fine, crowded, rounded, raised, concentric lines of growth which are apparently somewhat irregular in their development and distribution. Internally a slight median ridge extends anteriorly from the apex for about one-third the distance to the anterior margin of the valve. Remarks. — The above description is based upon the two cotypes of the species from Crawfordsville, Indiana. The brachial valve is incomplete posteriorly so that the exact position of its apex, relative to the posterior margin, cannot be determined. The length of the valve is also uncertain, and, since it is more or less crushed, the depth, as well as the contour of the sloping surface from the apex to margins, cannot be accurately deter- mined. The shell substance is largely exfoliated, but enough is preserved to show the character of the surface markings. The species is character- ized by its nearly circular outline and the nature of its surface markings. J7omo7i.— Keokuk (Crawfordsville shale). Orbiculoidea vabsoviensis (Worthen) Plate I, Pigs. 23, 24 1884. Discina varsoviensis Worthen, Bull. No. 2, 111. State Mus. Nat. Hist., p. 23. 1890. Discina varsoviensis Worthen, Geol. Surv. 111., vol. 8, p. 102, pi. 11, fig. 7. Description.— SiheU. rather large for the genvLs, subelliptical in outline. The dimensions of the holotype are : greater diameter 19.5 mm., lesser diameter 16.1 mm. Pedicle valve nearly flat; the pedicle opening situated excentrically in the line of the longer axis of the valve, and extending from the center of the valve half way to its posterior margin, its lateral margins elevated upon the internal surface of the valve to form an elongate, subovate prominence which is probably a depression or excavation externally. The external surface marked by sublamellose, concentric lines of growth, from two to three of which occupy the space of 1 mm. 42 . MISSISSIPPUN BEACHIOPODA Brachial valve imperfectly preserved in the only example observed, the degree of convexity not known, its surface marked by more or less regular, sublamellose, concentric markings similar in form and size to those of the opposite valve, and by very faint radiating costa? upon the flattened spaces between the concentric markings. Remarks. — Only two specimens of this species have been examined by the writer, these being the original types. The best preserved example is the inner surface of a pedicle valve which has been illustrated by Worthen. The second specimen is a fragment of limestone upon which two valves are crushed, partially overlapping, one apparently being a pedicle valve and the other a brachial. In its concentric surface markings the species resembles 0. keokuk, but it differs from that species in its subelliptical rather than subcircular outline. Horizmi.— Keokuk limestone. Orbiculoidea batesvillensis Weller Plate I, Pigs. 19, 20 1897. Orbiculoidea batesvillensis Weller, Trans. N. Y. Acad. Sci., vol. 16, p. 255, pi. 18, figs. 4-5. 1909. Lingulidiscina batesvillensis Girty, Bull. U. S. Geol. Survey No. 377, p. 22, pi. 1, figs. 12-12a. Description.—Shell subcircular or subovate in outline. The dimensions of two individuals, the cotypes, are: length 17 mm. and 16 mm., width 15.5 mm. and 17 mm., convexity 3.8 mm. and 3.5 mm. Pedicle valve not known. Brachial valve depressed convex, subcorneal, the apex small and in- conspicuous, inclined posteriorly, and situated excentrically from one- fifth to one-seventh the total length of the valve from the anterior margin, the greatest depth of the valve posterior to the apex, in some specimens notably so ; the surface gently convex throughout from the central portion to the margins, except for a short space back of the apex. The surface markings are concentric in arrangement so far as can be determined from the internal casts. Remarks.— This species was established upon two internal casts of the brachial valve especially characterized by their small apices which are distinctly lower than the greatest convexity of the valve anteriorly. It is possible that the apex of the valve would be somewhat more prominent in specimens preserving the shell itself, but it must always have been inconspicuous as compared with other species of the genus. fl^omo?!.— Batesville sandstone, Batesville, Arkansas. CRANIA 43 Family CRANIID^ Genus CRANIA Retzius J9escnp, often opening on the surface, the openings probably representing the broken bases of fine, hollow spines. Kemarks. — In external features the members of this genus are much alike in outline and general contour of the shell, and practically all of them, except H. diihia, might from their external characters aJone, be included in the European species R. michelinia as it has been interpreted by European authors. This interpretation of the American form has sometimes been suggested,^ but a most careful study of many examples has brought out the fact that essentially all of the species which have been described from our American Mississippian faunas are good species, although their most essential characters have not always been pointed out, and that several additional species must be recognized. The most important characters for use in the dift'erentiation of species are the form of the cardinal process and socket plates of the brachial iWeller, Bull. Geol. Soc. Am., vol. 20, p. 296 (1909). l-iS MISSISSIPPIAN BRACHIOPODA valve, and the size and strength of the muscular impressions of both valves. Externally the species differ somewhat in general proportions, contour and surface markings, and although these differences are fre- quently slight, they correlate with the more marked internal features. Rhipidomella missouriensis (Swallow) Plate XX, Figs. 1-8 1860. Orthis Missouriensis Swallow, Trans. St. Louis Acad. Sci., vol. 1, p. 639. 1892. OHhis Missouriensis Hall and Clarke, Pal. N. Y., vol. 8, pt. 1, pi. 6A, figs. 16-17. 1908. Rhipidomella missouriensis Rowley, Mo. Bureau Geol. and Mines, vol. 8, 2nd ser, p. 78, pi. 17, figs. 43-47. Description. —^heW lenticular in form, of medium size or a little smaller, suborbicular in outline, usually a little wider than long, the greatest width a little anterior to the middle, the hinge-line much shorter than the greatest width of the shell, the cardinal extremities rounded. The dimensions of two examples of about average size are : length of pedicle valve 19.7 mm. and 18.1 mm., length of brachial valve 19.1 mm. and 18 mm., greatest width 23.5 mm. and 20.5 mm., length of hinge-line 8.5 mm. and 9.5 mm., thickness 8 mm. and 9 mm. Pedicle valve most convex in the umbonal region, the surface curving somewhat abruptly to the cardinal margin and compressed towards the cardinal extremities, broadly flattened in the median portion of the valve and becoming gently convex towards the antero-lateral and anterior margins; mesial sinus obsolete or present only as a slight depression close to the anterior margin; beak small, pointed, a little incurved; car- dinal area small, concave, becoming more curved towards the beak, the inferior, flatter portion lying at an angle of about 45 degrees to the plane of the valve; delthyrium wider than high, its width at the base being from one-fourth to one-third the total width of the cardinal area. In- ternally the hinge-teeth are large, strong, and slightly diverging; the flabellate or subovate muscular scars reach anteriorly to the middle, or to a point beyond the middle of the valve, and are limited externally by a slightly raised border, the adductor impressions do not extend to the an- terior margin of the entire scar, but a raised median ridge continues an- teriorly to the limits of the diductor scars; the unpaired pedicle muscular scar occupies the rostral portion of the valve ; its surface is slightly raised above that of the contiguous sears in front and is sharply differentiated from them; the anterior and lateral margins of the valve are slightly thickened and crenulate internally. Brachial valve a little more convex than the pedicle, its greatest con- vexity near or a little posterior to the middle, the surface curving more RHIPIDOMELL.V 149 abruptly to the cardinal margin, slightly compressed towards the car- dinal extremities, towards the anterior margin the surface is gently convex and towards the 'lateral margins a little more strongly so; the median portion of the valve is slightly flattened and is not infrequently a little impressed along the median line to form a very shallow, ill- defined sinus, which, with the slight flattening of the opposite valve, sometimes makes the outline of the shell a little emarginate in front ; the beak is small, obtusely pointed and scarcely incurved ; the cardinal area is a little smaller than that of the opposite valve and lies in nearly the plane of the valve. Internally the cardinal process is rather large and is continued as a flattened median ridge along the floor of the valve dividing the quadripartite muscular impression ; the socket plates are prominent and widely diverging, with deeply excavated dental sockets; the muscular scars smaller and less deeply impressed than those of the opposite valve. The surface of both valves marked by nearly uniform, rounded costte, about three or sometimes four of which occupy the space of one milli- meter, and which increase by bifurcation and intercalation ; the shell sub- stance is pierced by radiating canals or tubes which follow the direction of the eosta> and which open at intervals to the exterior along the tops of the costa?. Regular, concentric lines of growth are usually present which often become more or less crowded towards the front margin. i^ewmrAs.— This species may be distinguished from R. hurlingtonensis, which it resembles, by its proportionally broader form, the smaller and less extended beak of the pedicle valve, by the somewhat more strongly developed radiating costse and by the less frequent openings of the radial canals upon the shell surface, all of which are of uniform size. The size of the species is usuallj^ less than that of R. burlingtonensis. Horizon. — Louisiana limestone. Rhipidomella burlingtonensis (Hall) Plate XXI, Figs. 5-7 ; Plate LXXXIII, Figs. 7-8 1858. Orthis michelini var. burlingtonensis Hall, Geol. Iowa, vol. 1, pt. 2, p. 596, pi. 12, figs. 4a-b. 1874. OrtJiis Michelini var. Biirli^igtcnensis? White, Prelim. Rep. Inv. Foss.. p. 17. 1892. Orthis Burlingtonensis Hall and Clarke, Pal. X. Y., vol. 8, pt. 1, pi. 6A, fig. 13. 1892. Orthis {Rhipidomella) Burlingtonensis Hall and Clarke, Pal. N. Y., vol. 8, pt. 1, pi. 20, figs. 5-6. 1894. Orthis iurlingtone-nsis Keyes, Mo. Geol. Surv., vol. 5, p. 63, pi. 38, fig. 7. Description.— Shell of medium size or larger, subovate in outline, the length and width nearly equal or wider than long, the greatest width 150 MISSISSIPPIAN BRACHIOPODA near or a little anterior to the middle, the hinge-line less than one-half the greatest width of the shell, the cardinal extremities rounded. The dimensions of two pedicle valves are : length 26.8 mm. and 24 mm., width 28.3 mm. and 25 mm., length of hinge-line 10 mm. and 11.8 mm., convexity 6.6 mm. and 6 mm. The dimensions of a large brachial valve are : length 28 mm., width 31.1 mm., convexity 6.5 mm. Pedicle valve most convex posterior to the middle, the umbo rather prominent, the surface sloping abruptly to the cardinal margins, some- times a little compressed towards the cardinal extremities, curving much more gently to the lateral and anterior margins ; the mesial portion of the valve broadly and indefinitely flattened anterior to the middle, some- times very slightly sinuate near the front margin ; beak rather prominent ; cardinal area small, concave, with the curvature increasing towards the beak, the lower, flatter portion sloping posteriorly at an angle of about 60 degrees to the plane of the valve, the lateral margins sharply defined, the delthyrium large and broadly triangular, its basal width sometimes occupying fully one-third of the total length of the hinge-line. Internally the cardinal teeth are of moderate strength and widely divergent; the muscular scars are large and flabellate with a slight raised marginal border, reaching beyond the middle of the valve anteriorly, sometimes being fully two-thirds the total length, with a width of from one-half to two-thirds the total width of the valve, the adductor sears are large and well defined, resting upon a somewhat elevated area near the middle of the entire muscular region which is continued anteriorly to the limits of the diductor sears in a raised median ridge somewhat narrower than the adductor scars themselves, the diductor scars are very large and are marked by several slight, subangular, radiating ridges, the unpaired pedicle muscle scar is large, occupying the entire rostral portion of the valve and is sharply differentiated from the contiguous scars in front ; the inner margin of the valve is crenulate anteriorly and laterally. Brachial valve subequally convex with the pedicle, the greatest con- vexity near the middle, the surface sloping with a gently convex curvature in all directions, the cardinal extremities sometimes slightly compressed; the mesial portion of the valve obscurely flattened or sometimes very slightly impressed in an ill-defined sinus; beak small, not incurved; car- dinal area small, lying in nearly the plane of the valve. Internally the socket plates are prominent, with their anterior extremities almost crura- like in form; they rest upon the floor of the valve through almost their entire length and are widely divergent ; the cardinal process is prominent and highly elevated, its posterior surface is nearly vertical and sometimes trilobate towards the apex, the anterior surface slopes obliquely to the floor of the valve and continues as a low, ill-defined mesial ridge to the anterior margins of the muscular scars ; muscular scars smaller than RHIPIDOMELLA 151 those of the opposite valve and less deeply impressed, quadripartite and subquadrate in outline; the inner margin of the valve crenulate anter- iorly and laterally. Surface of both valves marked by regular, uniform, depressed, rounded, radiating costa', from two to three of which occupy one millimeter. The shell substance is pierced by radiating canals or tubules of two sizes, which apparently follow the direction of the eostae, the larger ones open at intervals along the summits of the costa" while openings of the finer ones cover the sides of the costw and the furrows, giving to the shell, when a little weathered, the appearancfe of being punctate. Remarks. —Thin species is characterized by the prominent umbo of the pedicle valve, by the greatly elevated cardinal process of the brachial valve and by the large size of the muscular scars in the pedicle valve. In size it is about equal to K. owtni, but it is proportionally longer and has a much more prominent umbo on the pedicle valve and nearly or quite obsolete sinus in the brachial valve. It diflfers from K. jerseyensis in its coarser surface' costa?, the different position of the cardinal area of the pedicle valve, and in its much more prominent cardinal process. The punctate appearance of the shell surface is commonly more con- spicuous in this species than in any of the others here described, but this may be due to the different condition of preservation. /^orizoji.— Burlington limestone. Rhipidomella oweni Hall and Clarke > Plate XXI, Figs. 1-4 1882. Orthis Michelini (?) Hall, Rep. X. Y. State Geol. for 1882, pi. (6) 36. figs. 19-21. 1892. Orthis (Hhipidomella) Oiveni Hall and Clarke, Pal. N. Y., vol. 8, pt. 1, p. 342, pi. 6, figs. 19-21. 1897. Orthis {Rhipidtmiella) Oweni Hall, 14th Rep. N. Y. State Geol., p. 341, pi. 4, figs. 24-26. Description.— ^heW above medium size, lenticular in form, broader than long, with the greatest width anterior to the middle, the hinge-line about one-half or less than one-half the greatest width of the shell, the cardinal extremities rounded, the anterior margin nearly straight or somewhat emarginate in its median portion, curving regularly into the lateral mar gins at each side. The dimensions of two individuals are: length of pedicle valve 33 mm. and 27.5 mm., width 38 mm. and 32.3 mm., length of hinge-line 17 mm. and 17 mm., thickness approximately 9 mm. and 7 mm. Pedicle valve most convex at a point about half way between the middle and the beak, the surface curving more abruptly to the cardinal margin, very slightly or not at all compressed towards the cardinal extremities. 152 MISSISSIPPIAN BBACHIOPODA sloping with a gently convex curvature to the lateral and anterior mar- gins ; the mesial portion of the valve scarcely or not at all differentiated from the general surface in the umbonal region, in the median portion of the valve and towards the front there is usually a low, ill-defined, rounded, mesial fold bounded by much narrower, equally ill-defined, shal- low furrows, the top of the fold not being raised above the general convex curvature of the valve, near the front margin the median portion of the valve is commonly depressed to a slight degree in a broad, shallow, ill- defined sinus; the beak short and a little incurved; cardinal area small, eoncavely curved from the base to the apex, the lower, flattened portion sloping posteriorly from the plane of the valve at an angle of about 40 degrees, the lateral margins sharply defined, the delthyrium large, much broader than high, its width at the 1)ase about one-third, or nearly one- third, the total length of the hinge-line. Internally the cardinal teeth are strong and diverging, originating on either side of the delthyrium from the floor of the valve ; the muscular scars are subovate in outline and rather small for this genus, their total length usually being less than one-half the length of the valve ; they are rather deeply impressed, with a raised border, the adductor sears do not reach anteriorly as far as the diductors but in front of them, a distinctly elevated median ridge sepa- rates the two lobes of the diductor scars, the unpaired pedicle muscular scar occupies the rostral portion of the valve and is differentiated from the contiguous scars in front ; beyond the muscular scars the inner surface of the valve is pitted or is covered with faint, anastomosing ridges, and along the lateral and anterior margins it is crenulated, the crenulations corresponding in size with the exterior costse of the valve. Brachial valve about equally convex with the pedicle, the greatest convexity a little posterior to the middle, the surface sloping with a gently convex curvature to the lateral and anterior margins, a little com- pressed towards the cardinal extremities; a shallow, rounded, ill-defined mesial sinus originates in the umbonal region and continues to the anterior margin; the beak small and short, not incurved; cardinal area smaller than that of the opposite valve, its surface lying in nearly the plane of the valve. Internally the cardinal process is rather small and low, rising from the posterior extremity of a rather broad, elevated ridge occu- pying the median line of the interior of the valve and extending anteriorly from the apex of the valve to an ill-defined termination near the anterior margins of the muscular scars ; socket plates strong and widely diverging, resting upon the floor of the valve ; the muscular scars shorter and a little wider than those of the opposite valve ; the lateral and anterior margins of the valve crenulated internally. Surface of both valves marked by numerous, uniform, depressed, rounded, radiating costs, which increase by bifurcation and intercalation. RHIPIDOMELLA 153 about two or three of which occupy the space of one millimeter at the outer margin of a mature specimen of average size. Regular, concentric growth lines are present upon both valves, sometimes rather uniformly distributed but usually more crowded towards the front ; much finer con- centric lines may be also detected upon some shells. The shell substance is pierced by radiating canals or tubules of two sizes, following the direction of the surface eostae, the larger ones apparently occupy the position of the median lines of the costa?, along the summits of Avhich openings into the canals are present at irregular intervals, the finer canals occupy the slopes of the costiB and the intervening furrows, and upon slightly weathered specimens their openings are so numerous as to give to the shell a decided punctate appearance. Bemarks.—Asi connnonly preserved the shells of this species are crushed and often distorted, but a sufficient number of undistorted examples, mostly detached valves, have come under observation to show all the essential features of the species. The species is especially characterized by its proportionally broader form and smaller muscular scars of the pedicle valve than is iisual in the genus, and by the obscure and ill- defined mesial fold of the pedicle valve which is bordered on either side by an obscure rounded furrow. This latter character is not of sufficient strength to be preserved in the crushed examples, but in the undistorted valves it seems always to be present. The mesial sinus of the brachial valve is much stronger than the two furrows of the pedicle valve, and is a much more conspicuous feature than in R. burlingtonensis, the species which this one perhaps most closely resembles. 7/ori20»i.— Kinderhook (New Providence shale, Kentucky). Rhipidomella diminutiva RowJry Plate XX, Figs. 9-18, 30-35 1900. Rhipidomella diminutiva Rowlev, Am. Geol., vol. 25, p. 261, pi. 5, figs. 41-43. Descripticn. Shell Ti.sually a little below medium size, subovate in out- line, a little longer than wide or rarely with the length and breadth nearly equal, the greatest width anterior to the middle, the hinge-line from one- third to one-half the total width of the shell, the cardinal extremities rounded. The dimensions of three specimens are: length of pedicle valve 19 mm., 20 mm., and 19.3 mm.; length of brachial valve 18 mm., 19 mm., and 18.9 mm. ; greatest width 17.4 mm., 18.8, and 19 mm. ; thick- ness 8.8 mm., 10.2 mm., and 9 mm. ; length of hinge-line 6.5 mm., 7.5 mm., and 6.9 mm. Pedicle valve most convex posterior to the middle, the surface curving abruptly to the cardinal margin, more gently to the lateral margins and still more gently to the anterior margin, slightly compressed towards the cardinal extremities ; the median portion of the valve obscurely flattened 154 MISSISSIPPLVN BRACIIIOPODA anteriorly or sometimes with a slight, ill-defined median sinus; the beak ^mall, a little incurved, extending posteriorly only slightly beyond that of the opposite valve; cardinal area small, concave, with the curvature increasing towards the beak, the inferior, flatter portion sloping poster- iorly at an angle of from 50 to 60 degrees to the plane of the valve, the lateral margins sharply defined ; the delthyrium broadly triangular, much wider than high, its width at the base usually equal to a))out one-third the total length of the hinge-line. Internally the cardinal teeth are of moderate size and are widely divergent; the muscular scars are large, with their margin extending beyond the middle line of the valve, flabellate in outline, the adductor scars occupy a central, subcircular area, nearly one-third of the total length of the entire scar, which is distinctly raised above the general surface of the valve anteriorly and in front of which a gradually decreasing median ridge continues nearly to the limits of the diductor scars ; the unpaired, median pedicle scar is very large, occupying the entire rostral portion of the shell and encroacliing upon the adjacent scars in front from which it is sharply differentiated; the inner margin of the valve distinctly crenulate laterally and anteriorly. Brachial valve equally or a little more convex than the pedicle, with the greatest convexity posterior to the middle, the surface curving more abruptly to the cardinal margin, more gently to the lateral margins and most gently to the anterior margins, usually a little compressed towards the cardinal extremities; a shallow, rounded, rather narrow, ill-defined median sinus originates in the umbonal region and continues to the an- terior margin; the beak is inconspicuous, very obtusely pointed and not incurved ; the cardinal area much smaller than that of the opposite valve, lying in nearly the plane of the valve. Internally the cardinal process is erect, rather prominent, and obtusely pointed at the summit, the posterior face is subcarinate along its median line, becoming obscurely trilobate towards the summit, and is nearly vertical to the plane of the valve, the anterior face is transversely rounded and slopes rather abruptly to the front and is extended anteriorly along the inner surface of the valve as a rounded median ridge which flattens out and becomes obsolete at the anterior extremity of the muscular scars ; from either side of the cardinal process the socket plates originate and diverge widely, from the outer surface of each one a conspicuous lateral process limits the dental sockets, but beyond these processes the plates are produced into free, crura-like extensions; the muscular scars are distinctly quadripartite and are sub- quadrangular in outline, their anterior margin reaching to about the middle of the valve ; the inner margin of the valve is distinctly crenulate anteriorly and laterally. The surface of each valve is marked by fine, rounded, radiating costas, three or four of which occupy the space of one millimeter. These cosfee RHIPIDOMELLA 155 are nearly uniform in size and increase by bifurcation and intercalation, they are crossed by concentric lines of growth which vary in strength and position on different individuals. The shell substance is pierced by radiating canals or tubules of two sizes, which follow the direction of the costa', the larger ones open at more or less distant intervals along the summits of the costa% and openings of the finer ones are closely crowded throughout the entire intervening space, giving to the shell when in proper condition of preservation a distinctly punctate appearance. Remarls. — This species differs from R. hurlingtoncnsis in its somewhat smaller size, its finer costa?, its more elongate outline, and its more distinct mesial sinus of the brachial valve. Besides these external differences, the cardinal process is not so prominent as in K. burlingtonensis, and the socket plates are more distinctly produced into crura-like extensions than has been observed in that species. The species occurs near the summit of the Kinderhook and base of the Burlington limestone, occurrinji rather commonly in the white cherts of lower Burlington age at Louisiana, Missouri, which is the type locality. The species was originally described by Rowley from immature specimens about 6 mm. in length, the larger examples present in the same fauna being identified as R. burlingtonensis. A careful examination of speci- mens corresponding with the type of the species in size and in stage of development, and also of mature examples, has led the writer to the con- clusion that the small shells are certainly the young of the larger ones, although the smaller examples are proportionally somewhat broader than the mature ones. There seems to be, however, sufficient reason for the separation of these shells from R. burlingtoiensis, and consequently the name R. dimiuutiva must be extended to cover the mature as well as the younger representatives of the species. Horizon. — Upper Kinderhook and lower Burlington limestone. Rhipidomella thiemei (White) Plate XXI, Figs. 8-27 1880. Orfhi^'i tliif»Hi White, Contr. to Pal., No. 8, p. 164, pi. 41, figs. 4a-d. 1892. Orthis Thicmii Hall and Clarke. Pal. N. Y., vol. 8, pt. 1, pi. 6A, figs. 14-15. 1901. RJiipidomcUa burlingtonensis Weller, Trans. St. Louis Acad. Sci., vol. 11, p. 181, pi. 16, fig. 6. 1904. Rhipidmnella thiemei Girtv, U. S. Geol. Survey. Prof. Paper No. 21, p. 48, pi. 10. figs. 1-2. Description.— Shell small, subquadrate to subovate in outline, the length and width subequal or wider than long, the hinge-line much shorter than the greatest width, the cardinal extremities rounded. The dimensions of an undersized but very complete specimen are: length of pedicle valve 7.5 mm., length of brachial valve 7.4 mm., greatest width 8.4 mm., length 156 MISSISSIPPIAN BRACHIOPODA of hinge-line 5 mm., thickness 4.3 mm. The length of one of the largest pedicle valves observed is 12 mm. Pedicle valve depressed convex, the median portion of the valve broadly flattened from the beak anteriorly, the surface curving rather abruptly to the cardinal margin and much more gently to the lateral and anterior margins, very sliirhtly or not at all compressed towards the cardinal extremities ; mesial sinus originating near the mid-length of the valve and becoming rapidly deeper towards the front where it forms a rather conspicuous depression in the larger individuals; it is rounded in the bottom and ill-defined laterally; the beak is small, pointed and only a little incurved ; the cardinal area is small, moderately incurved, of mod- erate height, and is not very sharply defined at its lateral margins; the delthyrium is large and open and occupies fully one-half the entire car- dinal area. Internally the hinge-teeth are rather large and strong, and are supported by very short dental lamellae ; the flal)ellate muscular sears are large, reaching anteriorly beyond the middle of the valve, sometimes extending four-fifths the total length of the valve, the adductor scars are small, usually depressed below the general surface posteriorly, but ele- vated anteriorly and extended to the anterior margin of the diductor scars as an elevated ridge with gradually converging sides, the diductor scars very large and generally marked by radiating ridges. Brachial valve a little deeper than the pedicle and more regularly con- vex, the surface curving rather abruptly to the cardinal margin and more gently to the lateral and anterior margins, the mesial portion of the valve sometimes slightly flattened, but usually not differentiated from the gen- eral curvature; the beak small, obtusely pointed and not incurved; the cardinal area very small and lying in nearly the plane of the valve. In- ternally the cardinal process is large, its posterior surface is divided by a median ridge which slopes from the highest point towards the beak, the anterior surface drops nearly vertically to the floor of the valve, along which the process is continued as a median ridge of greater or less strength to about the middle of the valve ; the dental sockets are large and deep, the socket-plates are prominent and are produced anteriorly into slightly divergent, crura-like processes; the muscular scars are quadripartite, being smaller and much less deeply impressed than those in the pedicle valve. The surface of both valves marked by fine, rounded, radiating costfe which increase by bifurcation, from four to five occupying the space of one millimeter. More or less inconspicuous, concentric lines of growth are also usually present. Benmrks. — This is one of the smaller species of the genus, being com- parable in size to R dtibm. and R. jerseyensis only. It differs from R, jerseyensis, with which it is similar in general form, in the conspicuous mesial flattening of the pedicle valve, and the well developed mesial sinus RHIPIDOMELLA 157 in the anterior portion of the same valve, as well as in the absence of the mesial sinus of the brachial valve. From 7?. dubia it differs in its longer hinge-line and larger cardinal area, and in its more quadrangular outline. Horizon. — Upper Kinderhook. Rhipidomella jekseyensis n. sp. Plate XX, Figs. 36-43 1909. Rhipidomella michelinia Weller, Bull. Geol. Soc. Am., vol. 20, p. 295, pi. 12, figs. 8-10. DescriptioH. — Hhell small, wider than long, broadly subovate, frequently emarginate in front, the greatest width anterior to the middle, the hinge- line less than one-half the greatest width of the shell, the cardinal ex- tremities rounded. The dimensions of a nearly complete specimen of av- erage size are : length of pedicle valve 14 mm., length of brachial valve 13 mm., maximum width 15 mm., length of hinge-line 6.5 mm., thickness 6.7 mm. Pedicle valve most convex posterior to the middle, the surface curving abruptly to the cardinal margin and more gently to the lateral and ante- rior margins, the cardinal extremities usually somewhat compressed ; the median portion of the valve marked by an obscure, broadly rounded fold which is not defined laterally and which frequently becomes flattened out and obsolete anteriorly; the beak small, extending posteriorly only a short distance beyond the hinge-line; the cardinal area small, nearly flat or gently concave, its lateral margins sharply defined, sloping posteriorly at an angle of 30 degrees or less to the plane of the valve; the delthyrium large, broadly triangular, its width along the base being about one-third the total length of the hinge-line. Internally the cardinal teeth are of moderate strength and rather widely divergent ; the muscular scars are of moderate size, extending anteriorly less than one-half the length of the shell from the beak, and are only slightly depressed below the general internal surface of the valve; the lateral and anterior margins crenulate internally. Brachial valve nearly equally convex with the pedicle, its greatest con- vexity near or posterior to the middle, the surface sloping with a gently convex curvature in all directions, the cardinal extremities often a little compressed ; the median portion of the valve marked by a distinct but shallow, rounded, median sinus, originating in the umbonal region and becoming stronger anteriorly, not sharply defined laterally; the beak small, not incurved ; the cardinal area almost obsolete, lying in the plane of the valve. Internally the dental plates are rather prominent and widely divergent ; the cardinal process is very small, rising slightly from the posterior extremity of a rather broad, low, median ridge which ex- tends anteriorly along the floor of the valve to the anterior margin of the 158 MISSISSIPPIAN BRACHIOPODA muscular scars ; muscular scars rather faint, their anterior margin not reaching to the middle of the valve, obscurely quadripartite ; the lateral and anterior margins crenulate anteriorly. Surface of both valves marked by fine, depressed, radiating costse, about four or five of which occupy one millimeter along the front margin of an average size specimen. The cost* increase by bifurcation and inter- calation and remain nearly uniform in size. Crossing the costa? upon well preserved shells there are exceedingly fine concentric lines, and stronger, more or less irregularly distributed concentric lines of growth. The shell substance is pierced by radiating tubules which follow the direction of the costse, with openings at intervals along the summits of the costiE. Finer tubules, such as are present in R. burlingtonensis, have not been observed, although they may be present. Remarks.— This species occurs in great numbers in the Pern Glen Kin- derhook of Illinois and Missouri. It is characterized by its exceedingly fine costa^, by the distinct mesial sinus of the brachial valve, by the po- sition of the cardinal area of the pedicle valve which slopes posteriorly more nearly in the plane of the valve than in any other of the species here described, and in the small size of the cardinal process. By one or more of the above characters the species may be distinguished from any of the other species. In its typical expression this species is a small form, but associated with it are a smaller number of a much larger shell approaching R. burlington- ensis in size and form. The smaller specimens have usually been con- sidered as being the immature examples of the larger form, but many of the small individuals give every evidence of being fully mature, and it is more than probable that two species are represented. The larger one does not exhibit the distinct mesial sinus of the brachial valve which is such a marked characteristic of the smaller one, the cardinal area of the pedicle valve does not lie quite so near the plane of the valve, the cardinal process is more prominent and the muscular impressions are somewhat larger. Most of these characters, however, except the sinus of the brachial valve which ought to persist, might be due to the greater age of the larger shells. Horizcn.— Fern Glen formation. RniProOMELLA TENUICOSTATA n. sp. Plate XX, Figs. 27-29 Description.— Shell small, lenticular in form, subovate in outline, vary- ing from longer than wide to wider than long, the greatest width anterior to the middle, the hinge-line short, usually not exceeding one-third the width of the shell, the cardinal extremities rounded. The dimensions of two nearly perfect specimens are: length of pedicle valve 15.3 mm. and RHIPIDOMELLA 159 10.2 mm., length of brachial valve 14.6 mm. and 9.9 mm., maximum width 16 mm. and 10 mm., length of hinge line 5 mm. and 3.2 mm., thickness 6.7 mm. and 4.8 mm. Pedicle valve most convex posterior to the middle near the umbonal region, the surface curving abruptly to the cardinal margin and gently to the lateral and anterior margins, usually a little compressed towards the cardinal extremities; the mesial portion of the valve usually not dif- ferentiated from the general curvature of the surface ; the beak small, a little incurved; the cardinal area very small, sloping posteriorly in an angle not exceeding 25 degrees to the plane of the valve, sometimes ap- parently lying almost in the plane of the valve ; the delthyrium large, broadly triangular, its width along the base more than one-third the total length of the hinge-line. Internally the hinge-teeth are of moderate size and are widely divergent ; the characters of the muscular scars have not been satisfactorily determined, but they do not extend anteriorly beyond the middle of the valve ; the inner margins are crenulate anteriorly and laterally. Brachial valve about equally convex with the pedicle, the greatest con- vexity near the middle, the surface curving to the margins rather gently in all directions, the cardinal extremities sometimes a little compressed; the mesial portion of the valve either not differentiated from the general curvature of the surface or depressed in a slight mesial sinus which is narrow, shallow and ill defined laterally; the beak shorter and more ob- tusely pointed than that of the opposite valve, not incurved ; the cardinal area very small, lying in nearly the plane of the valve. Internally the cardinal process is large and strong, its posterior face transversely convex and sloping posteriorly from the summit at an angle of about 45 degrees to the plane of the valve, anteriorly it is continued along the median line of the inner surface of the valve as a conspicuous, broad, rounded ridge which reaches to about the middle of the valve ; the socket plates flank the cardinal process on either side, and are abruptly bent to an anterior direction, and for the greater part of their length they are parallel with each other and with the median line of the valve; the characters of the muscular scars have not been clearly determined. The surface of each valve is marked by exceedingly fine, nearly uni- form, radiating costa^ which increase by bifurcation and intercalation, about four or five occupying the space of one millimeter. The cost» are crossed by concentric lines of growth of moderate strength, varying in number and distribution upon different individuals. The shell substance is apparently perforated by radiating canals or tubules following the di- rection of the costff, which open at intervals along the summits of the costa> ; the presence of finer tubules in the intervening spaces is not clearly shown in any of the examples studied. 160 MISSISSIPPIAN BRACHIOPODA Remarks.— In its sniall size and fine costre, this species agrees most closely with R. jersey ensis, bvit it differs externally from that species in being proportionally more elongate and in the entire absence or very slight development of a mesial sinus in the brachial valve. Internally this species is totally different from R. jerseyensis in the characters of the cardinal process and socket plates, the cardinal process being exceed- ingly large and prominent, while in that species it is small. The median ridge along the inner surface of the brachial valve is much more strongly developed than in any other member of the genus here described. fl^amoH.— Chouteau limestone. Rhipidomella dubia (Hall) Plate XX, Pigs. 22-26 ; Plate LXXXIII, Figs. 9-10 1856. Orthis dubia Hall, Trans. Albany Inst., vol. 4, p. 12. 1863. Orthis Cooperensis Swallow, Trans. St. Louis Acad. Sci., vol. 2, p. 82. 1882. Orthis dubia Whitfield, Bull. Am. Mus. Nat. Hist., vol. 1, p. 45, pi. 6, figs. 1-5. 1883. Ortliis dubia Hall, 12th Ann. Rep. Geol. Surv. Ind., p. 324, pi. 29, figs. 1-5. 1892. Orthis dubia Hall and Clarke, Int. to Study of Brach., pt. 1, pi. 12, figs. 10-13. 1892. Orthis dubiu Hall and Clarke, Pal. N. Y., vol. 8, pt 1, pi. 6A, figs. 18-22. 1894. Orthis dubiu Keyes, Mo. Geol. Surv., vol. 5, p. 64. 1906. Rhipidcmella dubia Beede, 30th Ann. Rep. Geol. Surv. Ind., p. 1303, pi. 22, figs. 1-4. Description. — Shell small, usually a little longer than wide, subovate in outline, the greatest width usually anterior to the middle, the anterior margin nearly straight or slightly convex in the middle, sometimes slightly emarginate, the antero-lateral margins regularly rounded, the postero-lateral margins gently convex, becoming straighter as they ap- proach the beak where they meet usually in an angle a little less than a right angle, the hinge-line very short ; the two valves subequally convex. The dimensions of two individuals are : length of pedicle valve 14 ram. and 11.7 mm., length of brachial valve 13 mm. and 11 mm., greatest width 13.7 mm and 11.9 mm., thickness 8 mm. and 6.6 mm. Pedicle valve flattened medially in its posterior half, the surface curv- ing abruptly to the posterio-lateral margins, often with a slight incurva- ture to the cardinal extremities, and curving gently to the anterior and antero-lateral margins; mesial sinus rather broad and rather shallow, oi-iginating in or near the umbonal region, its lateral boundaries ill- defined, sometimes rather abruptly deepened as it approaches the anterior margin ; the beak compressed, slightly or only moderately incurved ; car- SCHIZOPHORIA 161 dinal area obsolete, the delthj-riuni rather large, about as wide or wider than high. Internally the hinge-teeth are large and strong, the muscular impressions large, flabellate, deeply impressed and usually extending two- thirds the length of the valve from the beak, the central or adductor im- pressions are situated upon a narrow, raised, median ridge; the anterior margin of the valve finely crenulated internally. Brachial valve more rotund than the pedicle, with its greatest convex- ity near the middle or a little posterior to the middle, from which point the surface curves to the margins in all directions, the curvature being a little more abrupt to the postero-lateral margins ; the mesial fold scarcely differentiated from the general convexity of the valve except sometimes near the anterior margin ; the beak pointed and slightly incurved. In- ternally the cardinal process is large and strong, sometimes extending anteriorly from the beak for one-fourth the length of the valve ; the mus- cular scars less deeply impressed than those of the opposite valve, divided along the median line by a narrow, elevated ridge ; the anterior margin of the valve finely crenulate interiorly. The surface of both valves marked by exceedingly fine radiating costa?, about three of which occupy the space of one millimeter at the front margin of a mature shell, these eostiv are commonly worn away from the greater portion of the valves so that their surface appears to be nearly or quite smooth, but they may usually be detected in the mesial sinus near the front of the pedicle valve where the surface is more protected than elsewhere. Remarks. — This species is a well-marked form, characterized by its small size, its short hinge-line and especially by the obsolete cardinal area, the marked flattening of the posterior portion of the pedicle valve and the more deeply depressed sinus near the front of the same valve than is common in the genus. The size of the species rarely exceeds that of the larger individual whose dimensions are given above, although the largest specimen observed has a length of 17 mm. and a width of 17.8 mm. The average size of the species is not far from that of the smaller example whose dimensions are given. Horizon. — Keokuk limestone, Warsaw formation and Salem limestone. Genus SCHIZOPHORIA King Description. — Shell subcircular or subelliptical in outline, resupinate or with the valves subequally convex. Hinge-line shorter than the great- est width of the shell, the cardinal areas rather low. The pedicle valve with short dental plates which are continued as rather sharp ridges along the floor of the valve bounding the muscular area. The muscular scars of the pedicle valve less than half the length of the valve, obcordate or subovate in outline, more or less deeply impressed in the substance of the —6 162 MISSISSIPPIAN BRACHIOPODA valve and bordered by elevated margins, divided longitudinally by an elevated ridge upon which are situated the adductor sears. In the brachial valve the socket plates are erect and divergent; the cardinal process is similar to that of Fhipidomella but becomes resorbed and narrowed with age ; the muscular scars are quadripartite and much less distinctly defined than those of the pedicle valve. Surface of both valves marked by fine, hollow, tubu'lose costiv, which are produced into short spines as in Rhipidmnella. ScHizoPHORiA suBELLiPTiCA (White and Whitfield) Plate XXIII, Figs. 1-5 1862. Orthis suhelliptica White and Whitfield, Proc. Bost. Soc. Nat. Hist., vol. 8, p. 292. 1870. Orthis subelliptica? Winchell, Proc. Am. Phil. Soc, vol. 11, p. 251. 1901. SchizopJiorm subelliptica Weller, Trans. St. Louis Acad. Sci., vol. 11, p. 182, pi. 16, %.s. 4-5 ; p. 196, pi. 19, figs. 6-7. Description.— Shell small, broader than long, transversely subelliptical in outline, the greatest width near the mid-length of the shell, the hinge- line about two-thirds the greatest width of the shell, the cardinal ex- tremities rounded. The dimensions of two pedicle valves are: length 10.8 mm. and 11 mm., width 13.5 mm and 13.8 mm., length of hinge-line 9 mm. and 9 mm., convexity 3.9 mm and 3.9 mm. Pedicle valve most prominent on the umbo, curving abruptly to the cardinal margin and gently to the anterior and antero-lateral margins, compressed towards the cardinal extremities; the mesial portion of the valve distinctly flattened anteriorly and usually depressed in an ex- ceedingly shallow, rather broad and ill-defined sinus; the beak pointed, rather prominent, a little incurved; cardinal area of moderate size, con- cave, the curvature increasing towards the beak, the lower, flatter portion lying at nearly a right angle to the plane of the valve, its lateral margins sharply defined. Internal characters not observed. Brachial valve not observed. Surface marked by fine, rounded, radiating costa;, increasing by bifur- cation and intercalation, every second or third one of which is slightly larger, about four or five occupying the space of one millimeter at the front of a mature shell 11 mm. in length. The shell substance pierced by radiating canals or tubules which follow the direction of the costa?, along the summits of the larger of which, the canals open at irregular intervals. Crossing the radiating costse are regular, concentric lines of growth, usually obscure or obsolete except near the margin where several are crowded together. Remarks. — In its typical expression this species has been recognized only in the fauna of the Kinderhook oolite bed at Burlington, Iowa, SCHIZOPIluRIA 163 although the cotypes of the species include specimens from the superjacent bed at the same locality. These latter specimens, however, grow to a much larger size, besides differing in some other respects, and should possibly be referred to the species here described as S. chouteauensis. In some respects S. subeUiptica suggests a diminutive S. swallovi, but the surface of the pedicle valve is much less flat than that species, with the beak and umbo proportionally more prominent. The radiating costae are also less nearly uniform in size in this species, with the external openings of the radiating canals restricted to the larger costaj. The brachial valve has not been available for study, but it is believed that it much more nearly equals the pedicle valve in convexity than in S, swallovi, in which species the convexity of the brachial valve greatly exceeds that of the pedicle. Homon.— Kinderhook. SCHIZOPHORIA CHOUTEAUENSIS n. sp. Plate XXIII, Pigs. 6-19 Description. — 'Sh^W of medium size or smaller, broader than long, trans- versely subelliptical in outline, the greatest width near the mid-length of the shell, the cardinal extremities rounded. The dimensions of two nearly perfect individuals are : length of pedicle valve 19.9 mm. and 12 mm., length of brachial valve 19 mm. and 11.8 mm., greatest width 22.8 mm. and 14.2 mm., length of hinge-line 14.4 mm. and 10 mm., thick- ness 11.2 mm. and 7 mm. Pedicle valve most convex near the umbo, the surface curving rather abruptly to the cardinal margin and more gently to the lateral and anterior margins, a little compressed towards the cardinal extremities ; mesial sinus entirely obsolete ; umbo prominent with the beak rather small and a little incurved; the cardinal area small, its lateral margins well defined, concave with the curvature increasing towards the beak the lower and flatter portion lying at nearly a right angle to the plane of the valve. Internally the cardinal teeth are supported by short dental lamellae which continue anteriorly along the inner surface of the valve as raised ridges bounding the muscular scars laterally ; the muscle scars fall short of reaching the middle of the valves anteriorly, they are subcordate in outline with a deep, acutely angular emargination in front, and are divided longitudinally by a raised, subangular ridge, which is highest anteriorly at the base of the emargination and is rather rapidly reduced in height posteriorly. Brachial valve a little more convex than the pedicle, the greatest con- vexity posterior to the middle, the surface curving abruptly to the car- dinal margin and more gently to the lateral and anterior margins, com- pressed towards the cardinal extremities ; the mesial portion of the valve 164 MISSISSIPPIAN BEACHIOPODA slightly flattened but not differentiated from the general curvature of the surface; beak smaller than that of the opposite valve and a little more incurved, projecting posteriorly beyond the cardinal line nearly as far as that of the pedicle valve ; cardinal area much smaller than that of the opposite valve, lying in nearly the plane of the valve. Internal characters not observed. Surface of both valves marked by fine, rounded, radiating costa; of nearly uniform size, which increase by bifurcation and intercalation, from three to four of which occupy the space of one millimeter at the front of a specimen about 20 mm. in length; crossing the radiating costaj there are regular concentric lines of growth which commonly become stronger and more crowded towards the front. The shell substance is pierced by radiating canals or tubules which follow the direction of the costce, along the top of which they open at intervals. Remarks.— This species resembles 8. suhelliptica but, besides being larger, it lacks the distinct mesial flattening of the pedicle valve and the slight depression near the front margin. On comparing examples of this species which correspond in size with mature specimens of S. suhelliptica, the cost® are considerably finer, there being as many a.s five in the space of one millimeter in an example 12 mm. in length at its front margin. The species differs from S. swallovi in its much smaller size, in the absence of the distinct flattening of the pedicle valve and in the more nearly equal convexity of the two valves. Horizon.— Chouteau limestone of the Kinderhook. SCHIZOPHORIA. SEDALIENSIS n. Sp. Plate XXI, Pigs. 28-32 Description.— Shell above medium size, broader than long, subelliptical in outline, the greatest width near the mid-length, hinge-line shorter than the greatest width, cardinal extremities rounded. The dimensions of a nearly complete individual are : length of pedicle valve 30.5 mm., length of brachial valve 30 mm., greatest width 36 mm., length of hinge-line 22 mm., thickness 17.8 mm. Pedicle valve most convex posterior to the middle, the umbo a little depressed, the surface curving abruptly to the cardinal margin and gently to the lateral and anterior margins, somewhat compressed towards the cardinal extremities; mesial portion of the valve broadly flattened towards the anterior margin ; beak small, a little incurved ; cardinal area small, sharply defined along its lateral margins, concave, with the curva- ture increasing towards the beak; the delthyrium broadly triangular. Internally the cardinal teeth are supported by short dental plates which are continued as low, angular ridges along the lateral margins of the muscular sears ; muscular scars subovate in outline, less than one-half the SCHIZOPHOBIA 165 length of the valve, not emarginate in front, divided longitudinally along the median line by an abruptly elevated angular ridge which is highest near the front and is gradually reduced in height towards the beak, in front of the muscular scar the median ridge is produced anteriorly as a flattened rib upon the inner surface of the valve. Brachial valve more convex than the pedicle, the greatest convexity posterior to the middle, the surface curving abruptly to the cardinal margin and more gently to the lateral and anterior margins, compressed towards the cardinal extremities; the median portion of the valve either not differentiated from the general curvature of the surface or broadly and indefinitely flattened from the umbonal region to the front ; the umbo a little produced beyond the cardinal margin, the beak small and in- curved; the cardinal area small, lying in nearly the plane of the valve. Internally the socket plates are prominent and widely divergent, the cardinal process is small, and is not produced as a median rib along the median line of the inner surface of the valve ; the muscular scars are subovate in outline and are about equal in size to those of the opposite valve. Surface of both valves marked by fine, radiating, rounded costfe which increase by bifurcation and intercalation, and about three of which occupy the space of one millimeter near the front of a mature example. The costa? are crossed by a few more or less indistinct, concentric lines of growth. The tubular nature of the costse has not been observed. Remarks.— This species most closely approaches S. stvallovi in its char- acteristics, but it differs from that species in the more convex pedicle valve and in the more nearly equal convexity of the two valves. In- ternally the shape of the muscular scars of the pedicle valve differs from those of 8. sivallovi in being without the emargination in front, and in having the median septum which divides the muscular sear longi- tudinally, produced anteriorly as a depressed ridge. In general contour the species most closely resembles 8. chouteauens-is, but it is larger than that species and has the pedicle valve indefinitely flattened towards the front, besides having the same difference in the form of the muscular sear of the pedicle valve as between it and 8. swallovi. Horizon.— JJpper Chouteau limestone. SCHIZOPHORIA POSTSTRIATULA U. Sp. Plate XXII, Figs. 7-14 (?15-17) 1909. Schizophoria swallovi Weller, Bull. Geol. Soc. Am., vol. 20, p. 296, pi. 12, figs. 6-7. Description.SheU resupinate, above medium size, wider than long, subelliptical in outline, the greatest width near the mid-length of the 166 MISSISSIPPIAN BRACHIOPODA shell, the hinge-line a little more than one-half the width of the shell, the cardinal extremities rounded. The dimensions of a nearly complete, somewhat crushed specimen, are : length of pedicle valve approximately 30 mm., length of brachial valve approximately 30 mm., greatest width 36.5 mm., length of hinge-line 20 mm., thickness 23 mm., convexity of pedicle valve 8.2 mm., height of cardinal area 4 mm. The dimensions of another nearly perfect but somewhat unsymmetrical specimen are : length of pedicle valve 28 mm., length of brachial valve 28.3 mm., greatest width 32.1 mm., thickness 19.2 mm , length of hinge-line 18.5 mm. Pedicle valve much less convex than the brachial, most prominent on the umbo, the surface sloping rather abruptly to the cardinal margin, and more gently to the lateral and antero-lateral margins, compressed towards the cardinal extremities ; the mesial portion of the valve slightly flattened in the posterior portion, becoming impressed anteriorly in a distinct, rounded mesial sinus of moderate depth; the beak moderately prominent and a little incurved ; cardinal area of moderate size, its lateral margins well defined, its surface concave with the curvature increasing towards the beak, the lower flattened portion with a slight posterior slope from the hinge-line ; the delthyrium of moderate size, about as wide as high. Internally the cardinal teeth are supported by short dental lamellae which are continued anteriorly along the inner surface of the valve as elevated ridges along the lateral margins of the muscular scar; muscular scar subcordate in outline with an angular emargination in front, less than one-half the total length of the valve, divided longitudinally by a strong, subangular, median ridge which is highest in front opposite the emargina- tion of the muscular region, gradually decreasing in prominence pos- teriorly. The brachial valve much more strongly convex than the pedicle, most prominent near the middle, the surface curving abruptly to the margin in all directions, slightly compressed towards the cardinal extremities, the umbo prominent and projecting conspicuously backward beyond the hinge-line ; the mesial portion of the valve slightly differentiated an- teriorly in a low, rounded, ill-defined mesial fold; beak pointed, much more strongly incurved than that of the opposite valve ; cardinal area about one-half as wide as that of the pedicle valve, concave, its lateral margins sharply defined, its inferior portion lying in nearly the plane of the valve and towards the apex curving towards the beak of the opposite valve. Internal characters not observed. Surface of each valve marked by fine, rounded, nearly uniform, radiat- ing costffi which increase by bifurcation and intercalation, about three costae occupy the space of one millimeter, the intervening furrows about equaling the costas in width ; crossing the radiating costag there are numer- ous, regular, concentric lines of growth which become stronger and more SCHIZOPHOEIA 167 crowded anteriorly where they are sometimes subimbricating. The shell substance is pierced by radiating canals or tubules which open at intervals along the summits of the costa;. Remarks.— This species has commonly been included in S. swallovi, but besides occurring at a lower horizon it possesses well-marked distinguish- ing characters. It never attains so great a size as S. swallovi, its pedicle valve is never so flat, it possesses a distinct mesial sinus toward the front of the pedicle valve, and instead of a slight mesial depression towards the front of the brachial valve there is a tendency towards a slight ele- vation or fold. In all these characters the species approaches the De- vonion 8. strialula, and it is essentially a form intermediate in character between this species and 8. swullovi. Horizon.— Fern Glen formation. SCHIZOPHORIA SWALLOVI (Hall) Plate XXII, Pigs. 1-6 1848. Orthis resupinata Christy, Letters on Geology, pi. 3, figs. 1-2. 1858. OrtUs swallovi Hall, Geol. Iowa, vol. 1, pt. 2, p. 597, pi. 12, figs. 5a-b. 1883. Orthis Swallovi Hall, Rep. N. Y. State Geol. for 1882, pi. (6) 36, figs. 23, 24. 1892. Orthis Swallovi Hall and Clarke, Pal. N. Y., vol. 8, pt. 1, pi. 6, figs. 23, 24. 1894. Orthis swallovi Keyes, Mo. Geol. Surv., vol. 5, p. 63, pi. 38, fig. 5. Description. — Shell large, resupinate, broader than long, transversely subelliptical in outline, often slightly emarginate in front, the hinge-line about one-half or a little more than one-half the greatest width, the car- dinal extremities rounded. The dimensions of two pedicle valves are: length 41 mm. and 38.5 mm., width 51.7 mm. and 49 mm., length of hinge- line 31 mm. and 23 mm., height of cardinal area 6 mm. and 4 mm., convex- ity 9.2 mm. and 7.5 mm. The dimensions of a brachial valve are: length 39.6 mm., width 46.2 mm., convexity 14.3 mm. Pedicle valve nearly flat or only slightly convex over the greater por- tion of its surface, most prominent in the umbonal region, curving some- what abruptly to the cardinal margin, a little compressed towards the cardinal extremities ; the median portion of the valve usually undifferen- tiated in the posterior half of the valve and becoming slightly depressed towards the front in a broad, shallow and undefined sinus, occasionally this sinus originates in the umbonal region, and sometimes it is slightly more depressed at either side towards the front with the median portion a little higher; beak rather small, only moderately produced beyond the hinge-line posteriorly ; cardinal area rather small, concave, with the curv- ature increasing towards the beak, broadly triangular, the lateral mar- gins well defined and usually slightly concave in passing from the beak 168 MISSISSIPPIAN BBACHIOPODA to the cardinal extremities, the inferior, flatter portion lying nearly at a right angle to the plane of the valve; the delthyrium large, broadly tri- angular. Internally the cardinal teeth are of moderate size, and are supported by short dental lamellsB which are continued anteriorly as low bounding ridges along the lateral margins of the muscular scars; the muscular scars rather large, sometimes extending anteriorly beyond the middle of the valve, sharply defined all around by a margin which is ab- ruptly raised from the inner surface of the valve, subcordate in outline with a deep and acutely angular emargination in front, divided longitud- inally from the base of the emargination to the beak by a conspicuous, narrowly rounded, median ridge which gradually decreases in size poste- riorly ; each lateral lobe marked by several ill-defined, more or less incon- spicuous, radiating ribs which are strongest anteriorly. Brachial valve much more convex than the pedicle, the greatest convex- ity posterior to the middle, the umbo prominent and extending conspicu- ously beyond the cardinal margin, the surface curving abruptly to the margin on all sides but most abruptly to the cardinal margin, somewhat compressed towards the cardinal extremities; the median portion of the valve distinctly flattened posteriorly, the flattened region becoming im- pressed towards the front in a shallow, rounded sinus of moderate width ; the beak pointed and rather strongly incurved ; the cardinal area smaller than that of the opposite valve, its lateral margins sharply defined, con- cave, curving from the hinge-line towards the beak of the opposite valve. The internal characters of the valve not observed. Surface of both valves marked by fine, regular, radiating costs which increase by bifurcation and intercalation, about two or three occupying the space of one millimeter at the front of a full grown shell, crossing the costffi are more or less irregular concentric lines of growth which are commonly more conspicuous upon the brachial valve, and are usually somewhat crowded near the margin of full grown shells. The shell sub- stance is pierced by fine, radiating canals or tubules which apparently follow the direction of the radiating costs, along the summit of which they open at intervals. Remarks. — This is the largest of our species of Schizophorm, and is a common and characteristic fossil of the Burlington limestone. It may be easily recognized by its large size and the very slight mesial sinus of the pedicle valve. Horizon. — Burlington limestone. CAMAKOPHOEIA 169 Family PENTAMERID^ Genus CAMABOPIIOlilA King Description.— Shell usually small or below medium size, rostrate, subo- vate to subpentagonal in outline, with well-developed median sinus in the pedicle valve and fold in the brachial valve, both valves either plicated or with the plications nearly or quite obsolete. In the pedicle valve the dental lamella are continued anteriorly into a well developed spondylium which is either supported by a median septum or rests directly upon the floor of the valve for a part or the whole of its length. In the rostral portion of the brachial valve the hinge-plate is continuous and is sup- ported by a strong median septum ; between the hinge-plate and the floor of the valve the median septum also supports a concave cruralium which is continued far beyond the hinge-plate, becoming broader and more highly elevated anteriorly ; posteriorly the median septum passes through the cruralium for the support of the hinge-plate, but the extension of the septum above the concave surface of the cruralium soon disappears be- yond the anterior margin of the hinge-plate. Fig. 1. — A series of eleven cross-sections (X 2%) of the rostral portion of Cam- arophoria schlotheimi (von Buch), the genotype of Camarophoria, from the Permian of Possneck, Germany, showing dental lamellae and spondylium of the pedicle valve, and the median septum, cruralium and hinge-plate of the brachial valve. i?emarA:5.— Sometimes the genus Camarophoria, has been so interpreted as to include a number of rhynchonelloid shells, R. subcuneata and R. suh- tiigona, of our Mis.sissippian faunas which are characterized by a median septum in both valves. These .shells, however, do not possess the cruralium of the brachial valve and are therefore excluded from the family Pentam- eridcE and are included in the present report in the Rhynchonellidw under the genus Tetracamera. In all the species here included in Camarophoria the characteristic internal characters of the shell have been determined by grinding the rostral portion of the shells. For comparison similar sections of the genotype, C. schlotheimi (von Buch), have been made and the American Mississippian species agree in all essential generic charac- ters with that species from the Permian of Germany. 170 MISSISSIPPIAN BEACHIOPODA Camarophoria hamburgensis Weller Plate XXIII, Figs. 52-60 1910. Camarophoria haniburgensis Weller, Bull. Geol. Soe. Am., vol. 21, p. 500, fig. 2. Description. — Shell below medium size, subovate in outline, the length equal to, greater or less than the width, the greatest width near the mid- length of the shell. The postero-lateral margins nearly straight, and meeting at the beak in an angle, the lateral and anterior margins rounded. The dimensions of a small but nearly perfect specimen are : length 9.4 mm., width 9.3 mm., thickness 5.5 mm. The dimensions of two detached brachial valves are : length 10.5 mm. and 10 mm., width 13.5 mm. and 12.4 mm. Pedicle valve depressed convex in the posterior half and towards the antero-lateral margins, more strongly arched from the beak to the ante- rior margin, along the postero-lateral margins the edge of the valve is rather abruptly inflected towards the opposite valve to form a false car- dinal area ; mesial sinus obsolete in the posterior half of the valve, orig- inating near the middle and continuing to the anterior margin as a broad, shallow, illdefined, regularly concave depression, whose surface curves towards the opposite valve anteriorly and is a little produced in front as a broad rounded extension; beak rather large, a little incurved, pierced by a subcircular foramen; delthyrium broadly triangular, nearly filled by the beak of the opposite valve, its apex communicating with the fora- men which encroaches upon the beak of the valve; plications depressed, r? r> o> o <^ r^ r^^ r^T^ Fig. 2. — A series of cross-sections of the rostral portion of the shell of Cam- arophoria hamburgensis (X 2%); A to J the pedicle valve; K to T the brachial valve. mostly simple, rather broad and rounded on top, originating at or near the beak, from 16 to 22 in number, from 5 to 7 of which occupy the mesial sinus, those towards the postero-lateral margins becoming faint or nearly obsolete. Internally the hinge-teeth are supported by dental lam- CAMAEOPHORIA 171 ellffi which are produced anteriorly more than one-third the length of the valve as a spondylium-like platform which rests upon the floor of the valve, not being raised on a median septum. Brachial valve more convex than the pedicle, the greatest convexity near the middle, the surface curving downward in all directions from the point of greatest convexity but more gently to the anterior margin than in other directions ; mesial fold obsolete in the posterior half of the valve, only moderately elevated in front, rounded transversely and sometimes scarcely difl'erentiated from the lateral slopes; the beak broad, strongly incurved beneath that of the opposite valve ; the plications similar in form and number to those of the opposite valve. Internally no cardinal pro- cess is present, the hinge-plate is broad and not divided and is produced anteriorly in a pair of crura, at the apex of the beak it is supported by a median septum from each side of which, at a position about midway be- tween the hinge-plate and the floor of the valve, springs a lateral process which curves slightly away from the floor of the valve, anteriorly the hinge-plate becomes entirely unsupported by the median septum before the articulation of the hinge is past, but the median septum itself with its transverse processes which develop into a broadly V-shaped platform extends for one-third or more of the length of the valve, the platform gradually rising higher above the floor of the valve and terminating ab- ruptly with the septum in front, posteriorly the median septum continues for a short distance towards the front as a gradually decreasing longitud- inal ridge in the bottom of the V-shaped platform. The surface of both valves, in addition to the plications, is marked by more or less obscure lines of growth. Remarks. — In its external aspects this little shell resembles, to some extent, some of the Devonian species of Pentamerella. but its internal characters are not essentially different from' those of Camarophoria, in which genus the species is placed without any hesitation. The spondy- lium-like platform of the pedicle valve resting upon the floor of the valve, is similar to the condition in Cam-arophorella, and the median septum of the brachial valve with its transverse processes is also similar to that genus, but it lacks the lateral septa which in that genus connect the outer margins of the V-shaped platform with the floor of the valve. Camaro- phorella has been shown recently to be a spire bearing shell,^ but there is no evidence in the specimens of the species here described that this form possessed any brachidium beyond the crura, although if such had been present it would have been destroyed in the separated valves which alone have been available for the examination of the internal parts. Externally, the shell is distinctly unlike Camarophorella in having distinct longitudinal plications. 1 Hyde, Proc. Boston Soc. Nat. Hist., vol. 34, No. 3, pp. 35-65 (1908). 172 MISSISSIPPIAN BRACHIOPODA Among the numerous examples of the species which have been exam- ined, a considerable amount of variation is exhibited in the proportional length and breadth of the shells and in the strength of the plications. An occasional example is found upon which the plications are essentially obsolete, and others occur on which they are obsolete towards the beak, but in all other respects, both external and internal, so far as they can be examined, they are identical with the plicated examples, and all are be- lieved to belong to a single species. Camarophoria bisinuata (Rowley) Plate XXIII, Figs. 20-45 1900. Seminula bisinuata Rowlev, Am. Geol., vol. 25, p. 263, pi. 5, figs. 21-24. 1909. Camarophoria bisinuata? Weller, Bull. Geol. Soc. Am., vol. 20, p. 301. Description.—SheW small, subovate to subpentagonal in outline, more or less subglobular in form, the length greater or a little less than the width, the greatest width near or in front of the middle of the shell. The dimensions of two examples, metatypes, are : length of pedicle valve 9.2 mm. and 9 mm., length of brachial valve 8.4 mm. and 8 mm., greatest width 9.8 mm. and 8.3 mm., thickness 6.1 mm. and 6.3 mm. Pedicle valve arched from beak to front, moderately convex in the umbonal I'egion, the curvature of the surface is abrupt and somewhat inflected from the umbonal region to the cardinal margin, and more gentle to the antero-lateral margins ; mesial sinus obsolete in the posterior half of the valve, rather broad and shallow anteriorly, deepest towards its lateral margins with a low, broad, rounded fold in the middle, pro- duced anteriorly in a lingual extension whose surface lies at nearly a right angle to the plane of the valve; beak small, pointed and moderately in- curved ; plications wanting except the broad, low, median fold which is usually present in the sinus. Internally, a strong median septum about one-third the length of the valve extends anteriorly from the beak, and supported by this septum is a distinct spondylium. Brachial valve more strongly convex than the pedicle, becoming gib- bous in the more globular examples, the greatest depth anterior to the middle and sometimes close to the anterior margin, the surface curving abruptly from the middle to the posterior, lateral and antero-lateral margins ; the median portion of the anterior half of the valve is elevated in a mesial fold which sometimes gives to the anterior portion of the valve a trilobed appearance, along its median line the fold is marked by a furrow which is commonly narrower than the median plication of the opposite valve; the beak is pointed and incurved beneath that of the opposite valve ; plications absent from the lateral slopes as in the pedicle CAMAKOPHORIA 173 valve. Internally a median septum, thinner and weaker than that of th^ pedicle valve extends anteriorly from the beak, and supports both the cniralium and the hinge-plate. The surface markings of the shell consist of rather strong, more or less regularly arranged concentric lines of growth. ^ (TO ^ © 9 Fig. 3. — A series of five cross-sections of the rostral portion of the shell of Camarophoria Msinuata (X 2%). Remarks. — This species was originally described as a member of the genus Seminula, now known under the name Composita, and in its gen- eral form it does resemble members of that genus. Some examples, even closely resemble small specimens of C. trinuclea, and under certain con- ditions of preservation it might be difficult to separate the forms, but internally the two shells are fundamentally different, the median septum and spoudylium being entirely wanting in Composita. The only other gpecies of Camarophoria with which it is necessary to compare this one is C. explanata. The more globular examples of C. hisinuata most closely resemble C. explanata, but they may always be distinguished by the absence of any plications upon the lateral slopes of the valves. Horizon.— Yevn Glen formation and lower Burlington limestone. Camarophoria explanata (McChesney) Plate XXIII, Figs. 46-51 1860. Rhynchonella explanata McChesney, Desc. New Pal. Foss., p. 50. 1865. Rhynchonella explanata McChesney, Plates 111. New Spec. Foss., pi. 6, figs. 7a-c. 1868. Rhynchonella explanata McChesney, Trans. Chicago Acad. Sci., vol. 1, p. 30, pi. 6, figs. 7a-c. 1894. Pugnax explanatus Hall and Clarke, Int. to Study of Braeh., pt. 2, pi. 44, figs. 14-16. 1895. Fugnax explanatus Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, pi. 60, figs. 43-45. 1897. Camarophoria explanata Schuchert, Bull. U. S. Geol. Survey No. 87. p. 162. !!910. Camarophoria explanata Weller, Bull. Geol. Soc. Am., ^ol. 21, p. 501, fig. 3. Description.— ^heW small, subglobular in form, usually a little wider than long. The dimensions of the type specimen, which is a little above the average size, are : length 8 mm., width 8.9 mm., thickness 7.5 mm. One of the largest examples observed has a length of 10 mm., but the 174 MISSISSIPPIAN BRACHIOPODA average size is probably a little less than that of the type specimen whose dimensions have been given. Pedicle valve strongly convex, the greatest convexity nearest the mid- dle, the surface strongly arched from beak to front and also transversely, the slope from the umbonal region most abrupt towards the cardinal mar- gin, more gentle to the lateral margins; mesial sinus obsolete in the posterior half of the valve, developed as a broad, shallow depression anteriorly and somewhat produced in front in a lingual extension whose surface is nearly at right angles to the plane of the valve; beak small, pointed, incurved ; plications obsolete posteriorly, in the anterior half of the shell they are broad and rounded, a single sti'ong one, the strongest one on the valve occupies the median portion of the sinus, and upon each lateral slope of the valve there are two or three weaker ones. Internally a strong median septum is developed, supporting a spondylium, which ex- tends anteriorly from the beak for one-third or one-half the length of the valve. QOQ(D Fig. 4. — A series of eleven cross-sections of the rostral portion of the shell of Camarophoria explanata (X 2%), showing the spondylium and the manner of development of the cruralium and its relation to the hinge-plate. Brachial valve gibbous, more strongly convex than the pedicle, the greatest convexity near the middle, the surface curving steeply from the middle point to the posterior, lateral and antero-lateral margins and more gently to the anterior margin; mesial fold obsolete in the posterior half of the valve and only moderately elevated in front, it is divided into two rounded folds by a median rounded furrow which originates near the middle of the valve to correspond with the median plication of the sinus of the opposite valve ; the beak is strongly incurved beneath that of the opposite valve; the plications are similar to those of the opposite valve; besides the two plications of the fold, already mentioned, there are two or three upon each lateral slope, none of which originate posterior to the middle of the valve and the smaller ones even nearer to the margin. In- ternally this valve has a median septum extending forward from the beak, but it is thinner and more feebly developed than that of the pedicle valve ; it supports the cruralium and the hinge-plate. CAMAKOTCECHIA 175 The surface is marked only by concentric lines of growth which are irregularly developed, frequently being obscure or wholly obsolete. Remarks.— In its general form this species resembles members of the rhynchonelloid genus Pugnax, but it differs fundamentally from members of that genus in having a distinct spondylium in the pedicle valve sup- ported by a median septum. This septum, and also that of the opposite valve, is almost always clearly recognizable, except in silicified specimens, as a dark line extending anteriorly from the beak. Hall and Clarke re- ferred the species to Pugnax doubtless because the specimen which they studied and illustrated was a very perfect sulphur cast of McChesney's type specimen, but upon which there was, of course, no color differentia- tion which would lead to the recognition of a septum. The species is very distinct from all other members of the genus in our American Mississippian faunas, and can be confused with none of thera. It occurs abundantly in some of the Chester faunas where it is a highly characteristic species. Horizon. — Chester group. Onier TELOTREMATA Family RHYNCHONELLID^ Genus CAMAEOT(ECHIA Hall and Clarke Description.— Shell rhynchonelliform, small or below medium size, subovate, subpentangular or subtriangular in outline. The mesial fold and sinus well developed, the surface of both valves marked by angular or subangular plications which extend to the beak, the plications not medially grooved in front. In the pedicle valve the hinge-teeth are rather small and are supported by slender, vertical, dental lamellse. Iti the brachial valve a well-defined median septum is present in the rostral portion of the valve which is divided internally to form a V-shaped cmral cavity, the hinge-plate is divided, the inner margin of each lateral portion being supported by one of the lateral walls of the crural cavity ; no car- dinal process is present and the crura are formed by the anterior extension of the inner margins of the two divisions of the hinge-plate. Remarks.— The essential generic characters of Camarotcechia are found in a combination of the internal and external features of the shell. The median septum of the brachial valve supporting the V-shaped crural cavity and the divided hinge-plate are identical in all essential respects with the rostral characters of Wilsonia., Liorhynchus, Paryphorhyiichus and Pugnoides, the five genera being differentiated one from another l;y constant external characters. In Wilsonia the shell is subcubical in form with the plications flattened anteriorly and longitudinally grooved, especially in the fold and sinus. Liorhynchus is a larger shell with the 176 MISSISSIPPIAN BRACHIOPODA plications usually nearly obsolete upon the lateral slopes of the valves. Paryphorhyiichits also is a much larger shell with the entire external surface of the valves marked by fine radiating striae in addition to the plications, and Pugnoides has the plications becoming obsolete towards the beak. Camabotcechia chouteauensis Weller Plate XXIV, Pigs. 34-40 1910. Camwotcechia chouteauensis Weller, Bull. Geol. Soc. Am., vol. 21, p. 510, fig. 10. Description. — Shell small and thick, triangularly subovate in outline, wider than long, the greatest width near or in front of the middle, the postero-lateral margins meeting at the beak in an obtuse angle, the lateral margins rounded, the anterior margin gently convex. The dimen- sions of two nearly perfect specimens are : length 11 mm. and 9.3 mm., width 11.5 mm. and 10 mm., thickness 10 mm. and 8 mm., width of sinus in front 7 mm. and 5.6 mm. Pedicle valve shallow, narrowly convex on the umbo, the surface sloping from the umbo to the cardinal margin, at first with an abrupt convex curvature, becoming gently concave as it approaches the margin, towards the antero-lateral margins the surface is gently convex and from the beak to the front along the median line it is strongly and nearly regularly arched ; the mesial sinus originates near the mid-length of the shell, it is abruptly depressed, its surface is nearly straight or slightly convex transversely across the bottom and is strongly curved towards the oppo- site valve longitudinally, anteriorly it is produced into a broad, elongate, lingual extension which lies in nearly a right angle to the plane of the valve, its greatest width is equal to about one-half the total width of the valve; the beak is small and moderately incurved; the delthyrium is nearly filled by the beak of the other valve, the deltidial plates and foramen are obscure and have not been observed in the specimens studied; the plications are shai-ply angular and originate at the beak, three or four occupy the bottom of the sinus, these being a little less angular than those upon the lateral slopes, each lateral slope bears from six to eight plications which become successively fainter towards the ^8888866 ^ ^ O H Fig. 5. — A series ot eight rross-sections of the rostral portion of the shell of Camarotachia chouteauensis (X 2i^), showing the characters of the median septum, crural cavity, hinge-plate, and crura of the brachial valve, and the dental lamellae of the pedicle valve. CAMAEOTCECHIxV 177 cardinal margin, the last two or sometimes three being almost obsolete. Internally, the hinge-teeth are supported by short, dental lamellae which scarcely extend bej^ond the articulation of the hinge. Brachial valve gibbous, the greatest depth at or near the anterior margin, the surface sloping from the anterior margin to the beak along the median line with a convex curvature which is a little flattened in the middle portion, the umbonal region flattened transversely with a dis- tinct longitudinal median depression which continues anteriorly for about one-fourth the length of the valve; the median fold not differentiated in the posterior half of the valve, flattened or gently convex on top and only moderately elevated above the lateral slopes anteriorly ; lateral slopes strongly convex longitudinally and curving abruptly to the margin of the shell laterally ; the beak strongly incurved beneath that of the opposite valve; plications similar in form and number to those of the opposite valve, those of the lateral slopes strongly arched longitudinally. In- ternally no cardinal process is present, the hinge-plate is divided and is supported towards the beak by a divided median septum which forms a crural cavity, the support of the hinge-plate by the divided median septum is discontinued posterior to the articulation of the hinge, but the free septvim continues for about one-third the length of the valve, gradually becoming lower until it disappears. A few obscure concentric lines of growth are sometimes present, but the shell is usually smooth aside from the plications. Remarks.— This little shell is a common form in the fauna of the Chouteau limestone and may be easily recognized by its size and angular plications. It differs from Rhynchoporaf cooperensis of the same fauna in its smaller size, relatively narrower shell and smaller number of plica- tions on the fold and sinus. Horizon. — Chouteau limestone. Camarotcechia elegantula Rowley Plate XXIV, Figs. 1-8 1900. Camarotcechia elegantula Rowley, Am. Geol., vol. 25, p. 264, pi. 5, figs. 44-47. Description.Sheli sntall, broader than long, the postero-lateral margins nearly straight or slightly concave and meeting at the beak in an angle of from 90 to 110 degrees, the antero-lateral and anterior margins rounded. The dimensions of three nearly complete specimens are : length of pedicle valve 7.5 mm., 9.5 mm., and 8.5 mm. ; length of brachial valve 7 mm., 8.5 mm., and 7.6 mm. ; greatest width 8.3 mm., 11.6 mm. and 9.4 mm. ; thick- ness 5.1 mm., 6.7 mm., and 6 mm.; width of sinus in front 6 mm., 8 mm., and 5.9 mm. 178 MISSISSIPPIAN BKACHIOPODA Pedicle valve convex in the umbonal region, the surface curving ab- ruptly to the postero-lateral margins and sloping with a gently convex curvature to the antero-lateral margins or sometimes becoming a little concave as it approaches the margin, from beak to front along the median line the curvature of the surface is nearly a semicircle ; mesial sinus orig- inating near the middle of the valve, of only moderate depth, nearly flat, or sometimes gently convex across the bottom transversely, produced an- teriorly in a rather broadly rounded or truncate lingual extension, the beak sharply pointed and incurved, obscuring the delthryium. Surface marked by sharply angular, simple plications which originate at the beak, there being from four to six on the bottom of the sinus and about five on each lateral slope of the valve, the largest plications of the valve are those bounding the sinus, those of the lateral slopes growing rapidly smaller, the last one towards the cardinal extremities being very faint or almost obsolete. Internally the dental lamellae are of moderate length and but slightly diverging anterior. Brachial valve more convex than the pedicle, the greatest depth near the anterior margin, posteriorly from the point of greatest convexity the surface slopes with a very gently convex curvature which becomes rapidly more convex in the posterior half of the distance, anteriorly from the same point the curvature is short and abrupt, laterally the surface curves rather abruptly to the margins from the median portion of the valve which is gently convex transvei'sely ; mesial fold originating near the middle of the valve, not conspicuously differentiated from the gen- eral convexity except towards the anterior margin; beak pointed and strongly incurved beneath that of the opposite valve. Surface marked by simple plications similar to those of the opposite valve but a little less angular. Internally a median septum reaches anteriorly from the beak for about one-third the length of the valve, this septum divides internally in the manner characteristic of the genus, forming a crural cavity between the margins of the divided hinge-plate. Minute surface markings obscure upon the specimen studied. Remarks.— The above description of this species has been prepared from specimens collected by Professor Rowley from the original locality and identified by him as being members of his species, specimens which are, therefore, metatypes. The species is characterized by a width greater than its length, its angular plications, and the variable number of plica- tions in the sinus. It differs from C. tuta, which is associated with it at the type locality, in its greater proportional width, its more angular plications, and the greater depth of the sinus in front. Horizon. — Lower Burlington limest/^ne (white chert.) CAMAROTCECHIA 179 Camarotcechia tuta (Miller) Plate XXIV, Figs. 9-28 1881. lihynchonella tuta Miller, Jour. Cinn. Soc. Nat. Hist., vol. 4, p. 315, pi. 7, figs, ll-llb. Description. Shell small, length and vndih subequal or somewhat longer than wide, subovate in outline, the greatest width near or a little anterior to the mid-length, the postero-lateral margins nearly straight, sometimes a little concave or a little convex, the antero-lateral and an- terior margins rounded or the anterior margin somewhat truncated. The dimensions of a nearly complete specimen from the type locality are: length of pedicle valve 6.4 mm., length of brachial valve 5.7 mm., greatest width 6.3 mm., thickness 4.5 mm., width of sinus in front 4.1 mm. The dimensions of a specimen from the Burlington white chert at Louisiana, Missouri, are : length of pedicle valve 7.3 mm., length of brachial valve 6.7 mm., greatest width 7.5 mm., thickness 5 mm., width of sinus in front 4.3 mm. Pedicle valve convex in the umbonal region, the surface curving ab- ruptly to the postero-lateral margins, gently convex from the umbonal region to the antero-lateral margins and arched in a subsemieircular curve along the mesial line from beak to front, with the posterior curvature a little more abrupt than the anterior: mesial sinus originating near the mid-length of the valve, nearly flat in the bottom transversely, produced anteriorly in a rather broadly rounded or subrectangular lingual ex- tension ; beak small, pointed, strongly incurved, coming nearly in con- tact with the umbo of the opposite valve, the delthyrium and deltidial plates obscured by the incurvature of the beak ; plications simple, originat- ing at the beak, rounded, becoming subangular towards the front, four usually if not always occupying the sinus, with about five upon each lateral slope which become successively smaller towards the cardinal ex- tremities ; concentric markings obscure or obsolete. Internally the dental plates are delicate and of moderate length, and are not widely divergent anteriorly from the beak. Brachial valve more strongly convex than the pedicle, the greatest convexity anterior to the middle, sometimes near the front margin, the surface arched from the beak to the front along the median line, usually with the curvature more pronounced posteriorly, the curvature more convex to the antero-lateral margins, becoming abrupt to the postero- lateral margins; mesial fold originating near the mid-length of the valve, not strongly differentiated from the general curvature of the valve except close to the anterior margin, in the umbonal region a shallow, longitudinal, bi'oadly subangular, mesial depression is present, which is deepest at the beak and becomes obsolete before the point of origin 180 MISSISSIPPIAN BRACHIOPODA of the mesial fold ; the beak strongly incurved beneath that of the oppo- site valve; the plications similar in form and number to those of the opposite valve and alternate with them, the concentric markings also similar to those of the opposite valve. Remarks, — This is a small species which was originally described from New Mexico and the above description has been drawn up from speci- mens collected at the type locality. Examples of the same species seem to be present in the Chouteau limestone of Missouri and Illinois, at least no characters have been detected which seem to be of sviffieient import- ance to differentiate the two forms, although the Chouteau limestone examples seem to be somewhat more rotund and have slightly less angular plications anteriorly in the sinus. Horizon. — Chouteau limestone and lower Burlington limestone. Camarotcechia sublogosa n. sp. Plate XXIV, Figs. 29-33 Description.— Shell small, subglobose in form, the outline subovate, the length greater than the width, the greatest width near the mid-length of the shell. The dimensions of a nearly perfect internal cast are : length of pedicle valve 12.5 mm., length of brachial valve 10.7 mm., greatest width 10.8 mm., thickness 9 mm., width of sinus in front 5.9 mm. Pedicle valve strongly convex, the greatest convexity near the middle, the surface curving abruptly to the postero-lateral margins, less abruptly to the antero-lateral and more gently to the anterior margin ; mesial sinus originating near or a little back of the middle of the valve, only slightly depressed below the general .surface, nearly flat transversely across the bottom, produced anteriorly in a rather .short and broad mesial extension ; beak rather prominent in the internal casts and only moderately in- curved ; plications simple, subangular, probably extending to the beak upon the external surface but becoming faint and obsolete towards the beak on the internal cast, three are present in the sinus and seven or eight upon each lateral slope, the last two or three towards the cardinal ex- tremities becoming faint and at last nearly obsolete ; rather crowded, fine, concentric lines of growth are present upon the internal cast over at least the anterior half of the valve, with an occasional stronger one, and upon the external surface these markings were doubtless strongly developed over the entire surface of the valve. Internally the dental plates are rather strong and of moderate length and between them is a well defined muscle scar which extends anteriorly for about one-third the length of the valve. Brachial valve subcircular in outline, but little more convex than the pedicle, its greatest convexity near the middle, the surface describing CAMAROTCECHIA 181 nearly a subsemicircular curve along the median line from the beak to the front, and curving rather abruptly to the lateral margins; mesial fold originating near the middle of the valve, only a little elevated above the general surface towards the front; the beak pointed and incurved be- neath that of the opposite valve; the plications and concentric markings similar in form and number to those of the opposite valve. Internally a strong median septum extends anteriorly from the beak nearly or quite to the center of the valve, in the rostral portion of the valve this septum divides internally forming a short crural cavity between the two lateral portions of the divided hinge-platt. Bemarks. — This species has only been observed in the form of internal casts from the residual Burlington chert of Knox County, Missouri, it may be easily recognized by its subglobose form, its rather coarse plications and its shallow mesial sinus and low fold. Formation.— BurlmgUm limestone (residual chert). Camarotcechia mutata (Hall) Plate XXIV, Figs. 41-60 1856. Rhynchonella mutata Hall, Trans. Albany Inst., vol. 4, p. 10. 1858. Rhynchonella mutata- Hall, Geol. Iowa, vol. 1, pt. 2, p. 658, pi. 23, figs. 2a-b. 1882. Rhynchonella mutata Whitfield, Bull. Am. ^Mus. Nat. Hist., vol. 1, p. 52, pi. 6, figs. 43-45. 1883 Rhynchonella mutata Hall, 12th R#p. Geol. Surv, Ind., p. 332, pi. 29, figs. 43-45. 1894. Rhynchonella mutata Keyes, Mo. Geol. Surv., vol. 5, p. 103. 1895. Pugnax mutatus Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, pi. 60, figs. 18-22. 1906. Pugnax mutata Beede, 30th Ann. Rep. Geol. Surv. Ind., p. 1306, pi. 22, figs. 43-45. Description. — Shell subovate or subtriangular in outline, usually wider than long, the greatest width in front of the mid-length of the shell, the postero-lateral margins straight or nearly straight, meeting at the beak in an angle of from 80 to 100 degrees, the anterior margin truncate, the antero-lateral margins more or less sharply rounded. The dimensions of two individuals are : length 9.7 mm. and 8.9 mm., width 10.6 mm and 9.1 mm., thickness 7 mm. and 5.5 mm., width of sinus in front 7.8 mm. and 5.8 mm. Pedicle valve convex in the umbonal region, usually somewhat flattened in the middle and towards the antero-lateral margins, the surface curves rather abruptly to the postero-lateral margins, gently to the antero-lateral margins and is arched from the beak to the front ; along the postero-lateral margins towards the beak, the edge of the valve is inflected to form a more or less indistinct pseudo-cardinal area, this area becoming less dis- tinct in the older shells ; mesial sinus obsolete in the posterior half of the 182 MISSISSIPPUN BRACHIOPODA shell, anteriorly it is broad and shallow, its surface is curved towards the opposite valve, and its anterior margin is produced more or less conspic- uously beyond the lateral margins; the beak is pointed, only slightly in- curved and is produced posteriorly beyond that of the opposite valve ; the delthyrium is broadly triangular and is partially closed by deltidial plates, with a subcircular foramen at the apex ; plications simple, suban- gular, becoming faint or obsolete close to the beak, fourteen to twenty in number, from three to six of which occupy the median sinus, the first two or three on each side nearest the postero-lateral margins are very faint. Internally the teeth are supported by short dental lamellae which do not continue anteriorly beyond the articulation of the hinge. Brachial valve more strongly convex than the pedicle, the greatest depth anterior to the middle and in adult shells near the anterior margin ; from the point of greatest convexity the surface curves more or less ab- ruptly to the anterior margin and more gently to the posterior extremity, laterally the surface curves somewhat abruptly to the postero-lateral margins, but the median portion of the valve is somewhat flattened trans- versely ; mesial fold scarcely defined except upon the more or less abrupt anterior slope of the valve and even there it is scarcely differentiated from the remainder of the valve; the beak strongly incurved beneath that of the opposite valve ; plications similar in form and number to those of the opposite valve. Internally no cardinal process is present, the hinge-plate is longitudinally divided to the apex of the beak and in the extreme posterior portion of the valve it is supported by a median septum which is divided above, each division of the hinge-plate being supported by one limb; the divided median septum with its crural cavity be- tween the divisions of the hinge-plate is extremely short and disappears posterior to the dental sockets, anteriorly the median septum is free and is reduced rapidly in height to a slight ridge along the bottom of the valve which sometimes continues for one-half the length of the valve ; the divided hinge-plate becomes nearly horizontal anteriorly where its anterior extremity is produced into the crura. The surface of both valves, aside from the plications, is nearly or quite smooth save for a few rather inconspicuous lines of growth near the an- terior margin of adult shells. Remarks. — This species is one of the abundant forms in the fauna of the Salem limestone. It was originally described from near Alton, Illinois, and in some of the Salem limestone localities in the bluffs above that city, it is particularly abundant. It is a variable shell, the variations being exhibited in the dimensions, convexity of the valves, fold and sinus, and number of plications. It differs from C. grosvenori, which occurs com- monly in the same fauna in Indiana, in its larger size, stronger and more angular plications and less globular form. CAMAEOTCECIIIA 183 The species has sometimes been referred to the genus Pugnax, but such reference is incorrect. Besides being quite different from typical mem- bers of that genus in external characters it possesses a crural cavity sup- ported by a median septum at the base of the divided hinge-plate a char- acter which is typical of the genus Camarotoechia. Horizon, Salem limestone. CAMAROTCECpiA GROSVENOEI (Hall) Plate XXIV, Figs. 61-72 1856. Rhynchonella Grosvenori Hall, Trans. Albany Inst., vol. 4, p. 10. 1882. lihyrichonella Grosvencri Whitfield, Bull. Am. Mus. Nat. Hist., vol. 1, p. 53, pi. 6, figs. 31-34. 1883. Rhynchonella grosvenori Hall, 12tli Ann. Rep. Geol. Surv. Ind., p. 331, pi. 29, figs. 31-34. 1895. Pugnax Grosvenori Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, pi. 60. figs. 13-17. 1901. Wilso7iia Grosvencri Whitfield and Hovey, Bull. Am. Mus. Nat. Hist., vol. 11, p. 388. 1906. Pugnax grosvenori Beede 30th Ann Rep Geol. Surv. Ind., p. 1305, pi. 22, figs. 31-34. 1910. Wilsonia grosvenori Weller, Bull. Geol. Soc. Am., vol. 21. p. 510, %. 11. Description. — ^heW small, subglobular in form, the width equal to, greater than or less than the length, the greatest width near or in front of the mid-length, the postero-lateral margins gently convex or nearly straight, meeting at the beak in an angle of 90 degrees or less, the ante- rior and antero-lateral margins more or less regularly rounded. The di- mensions of a large individual are : length 7 mm., width 6.5 mm., thick- ness 5.5 mm., width of sinus in front 4.5 mm. Pedicle valve more or less regularly convex throughout, the surface curving somewhat more abruptly to the postero-lateral margins, arched from beak to front ; for a short distance on each side of the beak the edge of the valve along the postero-lateral margins is somewhat abruptly and sharply inflected to form a small pseudo-cardinal area ; mesial sinus obso- lete in the posterior half of the shell and sometimes obsolete throughout, usually it is broad and slightly depressed anteriorly and is produced an- teriorly in a broad lingual extension which is curved towards the opposite valve to such an extent that its surface lies at nearly a right angle to the general plane of the valve in front; beak pointed, a little incurved and projecting posteriorly beyond the hinge-line; delthyrium broadly trian- gular, partially closed by deltidial plates, with a subcircular foramen at the apex which encroaches to some extent upon the beak of the valve ; plications simple, rounded, from 18 to 22 in number, two or three of which on each side near the cardinal margins are very small, from three to six are included in the mesial sinus, four or five being the more usual num- 184 . MISSISSIPPIAN BRACHIOPODA bers. Internally the teeth are supported by a pair of short dental plates which become obsolete anterior to the articulation of the hinge. Brachial valve more convex than the pedicle, the greatest depth anterior to the middle and sometimes close to the anterior margin, from the point of greatest convexity the surface curves more or less gently to the poste- rior extremity, transversely the surface is rather regularly convex but it curves a little more abruptly as it approaches the lateral margins ; mesial fold obsolete posteriorly and scarcely or not at all differentiated on the more or less abrupt anterior slope of the valve; the beak incurved be- neath that of the opposite valve ; plications similar in character and num- ber to those of the opposite valve. Internally the hinge-plate is divided to its base and the cardinal process is lacking, at the extreme posterior apex of the valve a median septum is present, which is divided above to support the two limbs of the hinge-plate forming a crural cavity, this " ? 9 9 O Fig. 6. — A series of five cross-sections of the rostral portion of the shell of Camarotcechia grosvenori (X 2%), showing the dental lamellae in the pedicle valve and the short median septum and small crural cavity in the brachial valve. cavity disappears posterior to the articulation of the hinge and the median septum is rapidly reduced in height, although it frequently persists as a slight median ridge to the middle of the valve. Aside from the plications the surface of both valves is nearly or quite smooth except in fully grown shells which have a few, distinct, parallel lines of growth close to the margin. Remarks.- — This species occurs commonly in the Salem limestone fauna in Indiana, but in the Illinois localities it is a rare shell. It resembles somewhat closely some of the variations of C. mutata, and in most large collections of the latter species a few individuals may usually be selected which by themselves might be referred to C. grosvenori. Typical repre- sentatives of the two species, however, are quite distinct. C grosvenori is a smaller species, much more globular in form, with a much less well developed sinus in the pedicle valve, and with finer and less angular pli- cations. Many and perhaps a majority of examples of C. grosvenori are longer than wide, while all but a very few specimens of C. mutata are wider than long. Most recent writers have referred this species to the genus Pugnax, but a careful examination of the internal characters shows such reference to be incorrect. With the small crural cavity between the bases of the divided hinge-plate, supported by a median septum, the species must be excluded from the genus Pugnax. LIORHYNCHUS 185 The species has sometimes been referred to Wilsonia, but it differs from members of that genus in the absence of longitudinal, median grooves upon the plications as they approach the anterior margin. Horizon. — Salem limestone. Genus LIORHYNCHUS Hall Description. — Shell usually of about medium size, subovate in outline and often subglobular in form. Mesial fold and sinus well developed, the plications obsolete or nearly obsolete upon the lateral slopes of the valves, more or less well developed on the fold and sinus. Internal characters of both valves as in Catnarotcechia, Remarks. — This genus has its greatest development in the Devonian faunas, but a few species are known in the Mi-ssissippian. The distin- guishing characteristic of the genus is found in the condition of develop ment of the plications, in combination with the median .septum and crural cavity of the rostral portion of the brachial valve. LIORHYNCHUS GREENIANUM (Ulrich) Plate XXV, Figs. 27-33 1886. Rhynchoiiella greeniana Ulrich, Cont. to Am. Pal., No. 1, p. 26, pi. 3, figs, 1-ld. 1895. Liorhynchus Greenianus Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, p. 194. 1895. Pugnax Greenianus Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, pi. 60, figs. 36-38. 1910. Leiorhynclius greeneanum Weller, Bull. Geol. Soc. Am., vol. 21, p. 511, fig. 12. Description. — Shell of miedium size or a little larger, subglobular in form, width usually a little greater than the length, the greatest width near the mid-length of the shell, the postero-lateral margins meeting at the beak in a rounded obtuse angle, the lateral margins rounded, the anterior margin usually broadly emarginate. The dimensions of a nearly complete specimen are: length 28.5 mm. width 28 mm., thickness 24.2 mm. Pedicle valve convex in the umbonal region, the surface nearly flat from just in front of the umbo towards the antero-lateral margins in a broadly V-shaped region, from each limb of this V-shaped region the surface curves abruptly to the postero-lateral margins on the outside and more gently into the sinus internally, from the beak to the front along the median line the surface is arched to form nearly a semicircle ; the mesial sinus originating near the middle of the valve as a broad, shallow, gently concave depression which becomes much deeper anteriorly; it is not sharply defined laterally and is produced in front in a broad, lingual ex- tension, rounded in front and usually concave transversely, and whose 186 MISSISSIPPIAN BRACHIOPODA surface anteriorly lies in nearly a right angle to the plane of the valve; beak rather blunt and short, incurved and nearly in contact with the umbo of the opposite valve, the delthyrium apparently broadly triangular and nearly filled by the beak of the opposite valve, the deltidial plates and foramen obscure and not observed in any of the specimens studied; plications almost obsolete, limited to from two to four, all of which are present in the anterior part of the sinus, having their origin near or in front of the middle of the valve. Internally the hinge-teeth are sup- ported by a pair of short dental plates which scarcely extend beyond the articulation of the hinge., G Fig. 7. — A series of seven cross-sections of the rostral portion of the shell of Liorhynchus greenianum (X 2%), showing the dental lamellae in the pedicle valve and the median septum and crural cavity in the brachial valve. Brachial valve gibbous, its convexity much greater than that of the ■pedicle valve, the surface strongly arched from beak to front along the median line with an increasing curvature towards the beak, laterally from the median line the surface curves abruptly to the margins, the curvature usually being a little broken towards the front by the differentiation of the mesial fold ; the mesial fold obsolete in the posterior half of the valve, usually but not always slightly differentiated anteriorly; the beak strongly incurved beneath that of the opposite valve; the plications similar to those of the opposite valve and restricted to the anterior portion of the mesial fold. Internally the cardinal process is wanting and the hinge-plate is divided ; at the apex of the valve a divided median septum is present, one side of which supports each side of the divided hinge-plate at its initial point, the space between the two divisions forming a crural cavity which, however, is very short and terminates before the articula- tion of the hinge is reached, beyond the crural cavity the septum is rapidly reduced in height and continues anteriorly for from one-fourth to one- third of the length of the valve as a faint ridge. PARYPHORHYNCHUS 187 The minute surface markings of the shell are preserved in none of the specimens studied, but concentric lines of growth, irregular in strength and distribution, are present upon all specimens examined. Remarks. — In its external form this species most closely resembles Shumardella obsolens, but it always grows to a much larger size and may be recognized by that character alone. Internally the two forms are quite distinct, L. greenianum having the hinge plate of the brachial valve completely divided, with the space between the two divisions of the median septum much broader, and the septum reduced in height much more rapidly. Both the internal characters and the external form agree with the genus lAorhyQichus, in which genus the species is placed un- hesitatingly. ilc-mon. —Knobstone formation, Indiana. Genus PAEYPHORHYNCHVS Weller Description.— SheUs rhynchonelliform, of medium size or larger, sub- ovate to transversely subrhomboidal in outline, mesial fold and sinus well developed, both valves marked by broad, rounded plications, which reach nearly or quite to the beak, surface of both valves also marked by fine, radiating striae which cover both the plications and the intervening furrows. The internal characters of the rostral portion of both valves entirely similar to CamarotcEchia. QQ F G Fig. 8. — A series of seven cross-sections of the rostral portion of the shell of Paryphorhynchus elongatum (X 2%), showing the dental lamellae of the pedicle valve and the median septum, crural cavity and crura of the brachial valve. Remarks. — In the arrangement of the internal structures of the rostral portion of the shell in this genus, there is nothing to differentiate it from Camarotoechia. The essential generic features are found in the external characters, viz., the broad plications and especially in the finely striate shell surface, in association with the camarotcechoid interior. 188 MISSISSIPPIAN BBACHIOPOUA Paryphorhvnchus transversum Weller Plate XXVI, Figs. 23-28 1895. Ptignax niissouriensis Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, pi. 62, figs. 44-45. (Not Rhynchonella missonrievsis Shumard, 1855.) 1900. Pugnnx striatocastata var. ? Weller, Trans. St. Louis Acad. Sci., vol. 10, p. 72, pi. 2, figs. 16-17. 1905. Paraphorhynchiis transversum Weller, Trans. St. Louis Acad. Sci., vol. 15, p. 264, pi. 1, figs. 12-15. Description.— ^thoW of medium size, wider than long, tran.sversely subelliptical in outline, the greatest width near the mid-length, the pos- tero-lateral margins nearly straight and meeting at the beak in an obtuse angle, the lateral and antero-lateral margins rounded, the anterior mar- gin gently convex. The dimensions of a nearly complete internal cast are : length 25 mm., width 31 mm., thickness 23 mm., width of sinus in front 19.5 mm. Pedicle valve flattened back of the umbo, the surface curving rather abruptly to the postero-lateral margin and usually incurved to some ex- tent, to the antero-lateral margins the surface is gently convex, and to the front it is strongly arched; the mesial sinus originates in or near the umbonal region and becomes rapidly deeper towards the front ; it is deeply concave anteriorly and is produced in a rounded lingual extension in front; the beak is obtusely pointed and rather sharply incurved; the plications are broad, subangular or rounded on top with furrows of about equal width separating them, three or more, usually four, are included in the sinus with about four upon each lateral slope of the valve, some- times the lateral plications of the sinus become obsolete towards the front. Internally the teeth are supported by a pair of diverging dental lamellae which extend anteriorly from the beak for about one-fourth the length of the valve. Brachial valve much more convex than the pedicle, the greatest con- vexity at or near the anterior margin, the surface sloping from the front to the beak along the median line with a gradually increasing curvature, posteriorly the surface curves abruptly towards the postero-lateral mar- gins and is slightly inflected, forming with the narrower incurved por- tion of the opposite valve a lateral concave region on each side of the beak ; mesial fold not diflferentiated in the umbonal region, at first gradually and then more strongly elevated towards the front, convex on top with rather steep sides, its width in front equal to nearly half the width of the shell ; the lateral slopes curving strongly towards the oppo- site valve both laterally and anteriorly; the beak strongly incurved beneath that of the opposite valve ; the plications are similar in form and number to those of the opposite valve, sometimes the two lateral plications of the fold coalesce with the next inner ones towards the front. Internally PARYPHORHYNCHUS 189 there is no cardinal process, the hinge-plate is divided to the base and its initial poi'tion is supported by a divided median septum forming a crural cavity at the base of the divided hinge-plate, the median septum continues with gradually decreasing height for about one-fourth the length of the valve from the beak. In addition to the plications the surface is marked by fine radiating strife, about four of which occupy the space of one millimeter, and by concentric lines of growth which are irregular in strength and distribu- tion but usually become more conspicuous anteriorly. Remarks. — This species, so far as known, is restricted in its distribution to some of the fine yellow sandstone formations in the Kinderhook at Burlington, Iowa; Washington County, Iowa; and Kinderhook, Illinois. It is miost closely allied to P. striaficostatum, but it attains a larger size than that species and is proportionally much wider with a more obtuse beak. Borne of the young individuals have more the outline of P. striaticostatvm, but as they increase in age they become more transverse. Horizcm. — Chonopectus sandstone of the Kinderhook. Parypiiorhynchus striaticostatum (Meek and "Worthen) Plate XXVI, Figs. 15-22 1868. Bhytichonella Missoiiriensis Meek and Worthen, Geol. Surv. 111., vol. 3, p. 450, pi. 14, figs. 7a-d. 1868. RhynchoneUa striata coat at a Meek and Worthen, Geol. Surv. 111., vol. 3, p. 452. 1895. Pugnax striato-costata Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, p. 204. 1895. Pugnax missourien-sis Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, pi. 60, figs. 33-34. 1901. Pugnax striatocostata Weller, Trans. St. Louis Acad. Sci., vol. 11, p. 154, pi. 13, figs. 14-16. 1905. Parapliorhynchus striatocostatnm Weller, Trans. St. Louis Acad. Sci., vol. 15, p. 262, pi. 1, figs. 6-11. Description.— Shell of about medium size, broadly subovate or subtrian- gnlar in oiitline, the width usually greater than the length, the greatest width near or anterior to the mid-length, the postero-lateral margins slightly convex or nearly straight, meeting at the beak in an angle of from 80 to 100 degrees, the antero-lateral and anterior margins regularly rovinded or with the anterior margin sometimes straightened. The dimen- sions of a nearly perfect specimen are: length 25 mm., width 26 mm., thickness 17.8 mm., width of sinus in front 18 mm. Pedicle valve shallow, the surface flattened towards the umbo, curving abruptly to the postero-lateral margins and sometimes becoming some- what inflected, curving gently to the antero-lateral margins and strongly arched from beak to front ; mesial sinus originating on or close to the um- bonal region, becoming deep and broad anteriorly, rounded in the bottom 190 MISSISSIPPIAN BRACHIOPODA and produced in front in a broad, rounded, lingual extension whose sur- face at the front of adult shells lies in nearly a right angle to the plane of the valve ; beak small, pointed, incurved so as to be almost in contact with the umbo of the opposite valve in full grown specimens, pierced at the apex by a very small subcircular foramen ; delthyrium broadly triangular, nearly tilled by the beak of the opposite valve, the deltidial plates incon- spicuous; plications coarse and strong, rounded, with furrows of about equal width between, three or four plications are usually present in the bottom of the broad sinus and three or four upon each lateral slope, mak- ing from nine to twelve upon the entire valve, the one nearest the postero- lateral margin on each side usually being faint or obscure. Internally the teeth are supported by a pair of dental lamellae which diverge ante- riorly and continue for about one-fifth of the length of the valve. Brachial valve much more convex than the pedicle, the greatest depth at or near the anterior margin, the surface sloping with a gradually in- creasing curvature from the anterior margin to the beak, from the median line the surface curves abruptly to the postero-lateral margins and towards the beak is sometimes a little inflected as it approaches the margin to form, with a similar inflected portion of the opposite valve, an ill-defined, slightly concave, lateral area on each side of the valve, in the anterior portion of the valve the surface passes from the median line with an ab- rupt double curvature, first to the border of the mesial fold and then to the lateral margins of the valve ; the mesial fold is ill-defined posteriorly but originates back of the middle of the valve and is strongly elevated in front where it is broad and rounded on top ; the beak is strongly incurved beneath that of the opposite valve, the plications correspond in form and number to those of the opposite valve with which they alternate. Inter- nally there is no cardinal process and the hinge-plate is divided to the base, being supported in its initial portion by a median septum which di- vides to form a crural cavity between the two divisions of the hinge-plate as in the genus Camarotoecliia. In addition to the plications the surface of both valves is marked by fine, radiating, longitudinal striae, about four or five of which occupy the space of one millimeter and by fine concentric lines of growth. On some examples stronger lines of growth are sometimes present at intervals. i?ewiorfcs.— This species can be ea.sily distinguished from the other mem- beers of the genus ParypJiorhynchus, by its smaller size and somewhat in- termediate character, it being distinctly shorter than P. elongatum and narrower than P. transversum. The species occurs most commonly in bed No. 4 of the Kinderhook section at Burlington, Iowa, and in a Kinderhook limestone near Kinderhook- Pike County, Illinois. The recorded occur- rence of the species in the Louisiana limestone of Missouri is probably an error. ffon'zoTi. —Kinderhook. PABYPHORHYNCHUS 191 Paryphorhynchus elongatum Weller Plate XXVI, Figs. 10-14 190b. Paraphorhynchus elongatum Weller, Trans. St. Louis Acad. Sci., vol. 15, p. 216, pi. 1, figs. 1-5. Description.Shell of medium size or larger, subovate in outline, longer than wide, the greatest width anterior to the middle, the postero-lateral margins nearly straight or gently convex and meeting at the beak in an acute angle of from 70 to 85 degrees, the anterior and antero-lateral mar- gins rounded. The dimensions of a nearly perfect specimen are: length of pedicle valve 37 mm., length of brachial valve 34.7 mm., width 28.8 mm., thickness 22.5 mm., width of sinus in front 23.8 mm. Pedicle valve strongly convex, the greatest convexity near or posterior to the middle, posteriorly the surface is regularly convex transversely in the central portion of the valve, but as it approaches the lateral margins it curves rather abruptly towards the opposite valve and is then continued in a nearly vertical or slightly inflected direction to the edge, from the beak to the front the surface describes nearly a semicircle in full grown shells, but to the antero-lateral margins the curvature is not so great ; the mesial sinus originates near the middle of the valve and is formed rather by the elievation of the borders above the general surface of the valve than by the distinct depression of the sinus itself, it is broad and is gently convex transversely across the depressed portion, anteriorly it is produced as a broad, rounded, lingual extension whose surface at the extreme margin lies at nearly a right angle to the general plane of the valve; the lateral slopes are narrow and ar6 abruptly elevated from the bottom of the sinus in front; the beak is small, sharply pointed, closely incurved and nearly in contact with the umbo of the opposite valve ; the delthyrium is broadly triangular and is nearly filled by the beak of the opposite valve, neither the deltidial plates nor the foramen has been ob- served, but both must bp inconspicuous; the plications originate near the beak and are broad and rounded on top with rounded furrows of about equal width between, they are from ten to fourteen in number, four or five of which occupy the sinus, the outermost plication of the sinus on each side frequently becomes obsolete before it reaches the anterior mar- gin. Internally the teeth are supported by a pair of strong dental 1am- elhe which may extend anteriorly from the beak from one-fifth to one- fourth the length of the valve. Upon the casts of the interior of the valve well defined but delicate pallial sinuses are clearly shown. Brachial valve equally or a little more convex than the pedicle, the greatest depth at or near the anterior margin, the surface curving from the anterior margin to the beak, along the median line, with a gradually increasing curvature which becomes rather abrupt near the beak; in the 192 MISSISSIPPIAN BRACHIOPODA median portion of the valve, posteriorly, the surface is regularly convex transversely, but near the postero-lateral margins it curves rather ab- ruptly towards the opposite valve and then continues in a nearly vertical direction to the margin where it meets the similar vertical surface of the opposite valve and forms the lateral flattened or slightly concave region which is present each side of the beak ; the mesial fold is obsolete in the umbonal region, is gradually elevated anteriorly to near the front margin where the elevation becomes abrupt, or rather the lateral slopes are curved abruptly towards the opposite valve, the fold is sharply defined and is nearly flat or slightly convex transversely across the top with ab- ruptly descending sides; the lateral slopes of the valve are narrow, their surface curves gently from the sides of the fold towards the lateral mar- gins for a short distance and then curves abruptly towards the opposite valve; the beak is incurved strongly beneath that of the opposite valve; the plications are similar in form and number to those of the opposite valve, one or more pairs upon the fold sometimes coalescing as they ap- proach the anterior margin. Internally no cardinal process is present and the hinge-plate is divided to the base, each division being supported by one side of a crural cavity which is joined to the floor of the valve by a median septum, the crural cavity continues to a point opposite the articulation of the hinge, beyond which the median septum becomes rapidly lower, the crura extend forward into the cavity of the shell from the anterior margin of the hinge-plate. In addition to the plications the surface of each valve is marked by fine radiating striae, four or five of which occupy the space of one milli- meter, and by still finer concentric striae with stronger lines of growth at intervals. Remarks. — In some of its aspects this species resembles the elongate, coarsely plicated shells of Ehynchotetra caput-Ustudinis with its flattened lateral areas on each side of the beak, but it is smaller than that species and more distinctly striated longitudinally besides possessing an entirely different internal structure, there being no median septum and spondy- limn in the pedicle valve. The species differs from P. striaticostatum in its larger size, more elongate form, more convex valves and the more con- spicuous, lateral, flattened areas on each side of the beak. Horizon.— Kinderhook. Genus PVGNOIDES Weller Description.Shells rhynchonelliforra, below medium size, subovate in outline, with the fold and sinus well developed. Both valves marked by rounded or subangular plications which become obsolete in the posterior portion of the shell. Internal characters of both valves essentially as in Camarotcechia. PUGNOIDES 193 Remarks. — This genus approaches more closely to Camarotaechia than any of those here considered, having camarota?ehoid interiors, although the genotype has usually been included in Pugnax, in which no median septum or crural cavity is developed in the rostral portion of the brachial valve. The members of this genus agree with Camaroto'chin in general size, and form, as well as in internal characters, being distinguished from that genus by the obsolescence of the plications towards the beak, in which character they are like Pugnax. PUGNOIDES OTTUMWA (White) Plate XXV, Figs. 7-17 1862. Bhynchonella Ottumwa "White, Proc. Bost. Soe. Nat. Hist., vol. 9, p. 23. 1880. Ehyncho')i£lla ottumwa White, Cont. to Inv. Pal., No. 8, p. 165, pi. 41, figs. 5a-c. 1894. Bhynchonella ottumwa Keyes, Mo. Geol. Surv., vol. 5, p. 103. 1895. Pugiiax Ottumwa Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, pi. 60, figs. 23-26. 1910. Pugnoides ottumwa Weller, Bull. Geol. Soc. Am., vol. 21, p. 512, fig. 13. Description.— Shell below medium size, siiboval to subpentagonal in outline, usually wider than long, the greatest width usually anterior to the mid-length of the shell. The dimensions of two individuals are: length 12 mm. and 10.7 mm., wndth 12.5 mm. and 11.3 mm., thickness 8 mm. and 6.3 mm. Pedicle valve with rather long, nearly straight postero-lateral margins which meet at the beak in an acute angle, the lateral and anterior mar- gins rounded, the surface convex in the umbonal region, curving abruptly to the postero-lateral margins, less abruptly to the anterior margin and only gently convex or nearly straight to the antero-lateral margins ; along 9 o Q <& '^ G M I J K Pig. 9. — A series of eleven cross-sections of tiie rostral portion of the shell of Pugnoides ottumwa (X 2%), showing the dental lamellae of the pedicle valve and the median septum, crural cavity and crura of the brachial valve. the postero-lateral margins towards the beak, the edge of the valve is ab- ruptly inflected to form a sort of false cardinal area ; mesial sinus obso- —7 • 194 MISSISSIPPIAN BHACHIOPODA lete in the posterior half of the valve, becoming rather broad and deep anteriorly and somewhat produced in front in a linguiform extension which curves strongly towards the opposite valve ; the beak acutely pointed, only a little incurved, produced posteriorly beyond the brachial valve to a conspicuous degree ; delthyrium large and triangular, partially closed by a pseudo-deltidium, with a large, subelliptical foramen ; plica- tions simple, obsolete towards the beak but originating in or near the umbonal region, gradually increasing in strength until they become con- spicuously subangular towards the margin, usually two or three are pres- ent in the bottom of the sinus, more rarely one, four or five, upon each lateral slope there are usually three but sometimes only two strong pli- cations, with from one to four additional weaker ones towards the car- dinal margin. Internally the teeth are supported by a pair of short dental plates. Brachial valve more convex than the pedicle, the greatest convexity near the middle, from the center of the valve the surface curves most abruptly to the postero-lateral margins, more gently to the posterior extremity and to the antero-lateral margins, and extends nearly horizon- tally to the anterior margin; mesial fold obsolete posteriorlj^ becoming somewhat strongly elevated in front; the beak incurved beneath that of the opposite valve; plications entirely similar to those of the opposite valve, three or four usually present on the fold- but sometimes two or five, two or three strong ones on each lateral slope, and several weaker ones. Internally the valve bears a median septum which is somewhat rapidly reduced in elevation in passing from the beak anteriorly, becom- ing entirely obsolete in about one-thivd or less the length of the valve, posteriorly the septum is divided to form a crural cavity which does not continue anteriorly beyond the hinge sockets, each side of the divided septum is produced anteriorly into one of the lateral divisions of the hinge plate, and these in turn are produced into the somewhat elongate crura which curve towards the pedicle valve. Surface of both valves usually quite smooth aside from the plications, except near the margin of adult shells where there may be several more or less distinct lines of growth, sometimes a more or less distinct line of growth is present in the umbonal region and when present it usually marks the place of origin of the plications. Remarks. — This shell is usually a prolific species wherever it is found. It occurs most abundantly in the Pella beds of loAva, but is also a con- spicuous species in some of the Ste. Genevieve beds of Illinois. The species may be easily recognized by its smooth shell, aside from the plica- tions, by the conspicuously protuberant beak of the pedicle valve, and by the inflected cardinal margin of the pedicle valve to form a false cardinal area. PUGNOIDES 195 The species has been referred to the genus Pugnax by Hall and Clarke, but the internal structure of the braehial valve is that of Cam-arotoBchia rather than Pugnax. The specimen figured by these authors as the braehial valve of the species with its broadly divided hinge-plate unsup- ported by a median septum, must be either incomplete or it must be some- thing else. Repeated sections of authentic examples from Pella, Iowa, show the camerotoechoid characters here described and illustrated. Horizon. — Ste. Genevieve limestone. PuGNOiDES BOONENSis (Shumard) Plate XXV, Pigs. 22-26 1855. Rhynchonella Boonensis Shumard, Geol. Rep. Mo., p. 205, pi. C, figs. 6a-b. 1894. Rhynchonella hoonensis Keyes, Mo. Geol. Surv., vol. 5, p. 101. 1895. Leiorhynchus {?) Boonensis Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, pi. 60, fig. 35. Description.— 'SheW of about medium size, broadly ovate-subtriangular in outline, wider than long, the gi-eatest width near the mid-length, the postero-lateral margins nearly straight and meeting in an obtuse angle, the antero-lateral margins rounded, the anterior margin sinuate. The dimensions of a nearly perfect specimen are : length of pedicle valve 19.1 mm., length of brachial valve 17.9 mm., greatest width 24 mm., thickness 17 mm., width of mesial sinus of pedicle valve in front 17 mm. Pedicle valve gently convex in the umbonal region, flattened towards the antero-lateral margins, strongly arched from beak to front along the median line, the curve forming nearly a semicircle, narrowly but rather abruptly curved along the postero-lateral margins and a little inflected to the cardinal extremities; mesial sinus originating near the mid length of the valve, becoming broad and rather deep anteriorly and produced in a broadly rounded lingual extension whose surface lies at nearly a right angle to the plane of the valve ; the beak obtusely pointed and only a little incurved; plications obsolete upon the posterior portion of the valve, but a little developed in front of the middle, those of the sinus, two in number, originating near the mid-length of the valve, rounded on top and becoming stronger towards the anterior margin, on one or both sides of this pair of strong plications there is sometimes a much fainter plication initiated near the margin ; on each side of the mesial sinus upon the lateral slopes one or two faint plications are com- monly present which are limited to the extreme margin of the valve. Internally the dental lamella> are short, between them in the rostral por- tion of the valve is a short, low, median ridge, but anteriorly, beyond the extremities of the lamellae the inner surface of the valve is somewhat excavated for the muscular attachment. 196 MISSISSIPPIAN BBACHIOPODA Brachial valve strongly convex transversely and moderately convex from the beak to near the front along the median line, the greatest con- vexity of the valve near the front margin, the anterior slope very short and curving somewhat abruptly to the anterior margin; mesial fold not differentiated from the general convexity except towards the anterior margin, and even there the differentiation is not conspicuous; the beak pointed and incurved beneath the beak of the opposite valve ; three short but rfither strong plications are present anteriorly upon the mesial fold, and one or two fainter and even shorter ones upon each lateral slope, 888$ Pig. 10. — A series of six cross-sections of tlie rostral portion of the shell of Pugnoides boonensis (X 2i/^), showing the dental lamellse and slight median septum of the pedicle valve, and the median septum, the small crural cavity and the crura of the brachial valve. the greater portion of the valve posteriorly entirely non-plicate. In- ternally a well developed median septum is present which extends an- teriorly upon the interior surface of the valve for more than one-third the length of the valve, in the rostral portion of the valve the median septum is divided internally to form a crural cavity such as is present in this genus, the crural cavity is very short and terminates posterior to the articulations of the valves, the crural bases joined to the hinge-plate for a short distance beyond the termination of the crural cavity. Surface of both valves marked by fine, obscure, but rather regular, concentric lines of growth, with an occasional stronger and more or less conspicuous one; radiating strije not present. Remarks.— This species approaches the European Ptignax pugnus more nearly in its external form than any other of our American Mississippian rhynchonelloids, but the internal characters of the shell differentiate it ALLORHYNCHUS 197 from the genus Pugnax and bring it in conformity with the members of the genus Pugiwides which possess the median septum in the brachial vave and the crural cavty between the opposite parts of the divided hinge- plate. The species is one of the rarest forms in the lower Burlington lime- stone. Horizon. — Fern Glen formation, lower Burlington limestone. Genus ALLORHYNCHUS Weller Description. Shells rhynchonelliform, small or below medium size, with mesial fold and sinus well developed and both valves marked by sub- angular or rounded plications which are usually well defined to the beak. Interior of the pedicle valve with slender dental lamella?. In the brachial valve the hinge-plate is divided, the inner edges of each lateral portion being unsupported, no median septum and no crural cavity, such as is present in Camarotoechia are developed. Remarks.— In external features the members of this genus are not essen- tially different from CanmrotoBchia, but an examination of the interior of the rostral portion of the brachial valve shows that they are not at all alike. In the entire absence of lamellae of any sort for the support of the hinge-plate of the brachial valve, Allorhyiuhus is like Pugnax, but it differs from that genus in the completely plicated shell. Alloehynchus heteropsis (Winchell) Plate XXIV, Figs. 73-81 1S65. Rhynchonella heteropsis Win., Proc. Acad. Nat. Sci. Phil., p. 121. 1901. Camarotoechia (?) heteropsis Weller, Trans. St. Louis Acad. Sci., vol. 11, p. 156, pi. 13, figs. 9-13. 1910. Allorhynchus heterop»is Weller, Bull. Geol. Soc. Am., vol. 21, p. 509, fig. 8. Description.— Shell small, triangularly subovate in outline, usually wider than long, the greatest width anterior to the mid-length of the shell, the postero-lateral margins nearly straight or a little sigraoidal and meeting at the beak in an angle from 90 to 108 degrees, the antero-lateral margins rounded and the anterior margin straight or convex. The dimensions of two individuals are: length 11.1 mm. and 12 mm., width 13.6 mm. and 12 mm., thickness 7.5 mm. and 6.4 mm., width of sinus in front 9.3 mm. and 7 mm. Pedicle valve convex on the umbo, the surface curving rather abruptly to the cardinal margin with the edges of the valve narrowly inflected for a short distance on each side of the beak, towards the antero-lateral margins the surface is gently convex or flattened and from the beak to the front margin it is rather strongly arched; the sinus originates near 198 MISSISSIPPUN BRACHIOPODA 01* a little back of the middle of the valve and becomes rapidly deeper anteriorly and is moderately produced in a broad, rounded extension in front, "where its width is about one-half the total width of the shell ; it is usually nearly flat across the bottom in front with the sides sloping out- ward or rarely nearly vertical ; the beak is acuminate and sharply pointed and is strongly incurved, coming nearly in contact with the umbo of the opposite valve ; the delthyrium is nearly filled by the beak of the opposite valve, the deltidial plates and foramen are obscure and have not been clearly recognized in any of the specimens studied; the plications are simple, angular, rather coarse, and originate at the beak, three or rarely four occupy the bottom of the sinus with sometimes an additional one upon each sloping side, with from four to six upon each lateral slope of the valve, the plications of the lateral slopes nearest the margins of the sinus are the strongest and most angular ones on the valve. Internally the hinge-teeth are weak and are supported by a pair of short, thin, dental lamella;. 9 0 0 9 9 o F Fig. 11. — A series of six cross-sections of the rostral portion of the shell of Allorhynchus heteropsis (X 2i/^), showing the presence of dental lamellae in the pedicle valve and the entire absence of lamellae in the brachial valve. Brachial valve much more convex than the pedicle, its greatest convex- ity at or near the front margin, the surface slopes along the median portion of the shell from the front margin to the beak with a regular or with an increasing curvature, at the umbo the surface is impressed along the median line in a shallow but distinct sinus which continues to the middle of the valve either as a distinct sinus or as a flattened surface, to the postero-lateral margns the surface slopes first with a convex curvature and then becomes flattened or sometimes even concave; the mesial fold is scarcely distinct back of the middle of the valve but anteriorly it is rather strongly and abruptly elevated above the lateral slopes; the lateral slopes are convex with the surface curving rather strongly both anteriorly and laterally; the beak strongly incurved beneath that of the opposite valve ; the plications are similar in form and number to those of the opposite valve. Internally the hinge-plate is divided to its base and lacks supporting septa of any kind, the cardinal process and median septixm wanting. Remarlis, — In its usual condition of preservation the surface of this species is exfoliated so that all indication of minute surface markings is destroyed, but upon remnants of the shell which are sometimes present ALLORHYNCHUS 199 extremely fine, crowded concentric striae can be detected. Occasionally stronger lines of growth are present, but they are never conspicuous. Horizon. — Kinderhook. Allorhynchus macra (Hall) Plate XXV, Figs. 1-6 1856. Rhynchonella macra Hall, Trans. Albany Inst., vol. 4, p. 11. 1856. Rhynchonella ricimda Hall, Trans. Albanv Inst., vol'. 4, p. 9. 1882. Rhynchoiiella macra Whitfield, Bull. Am.' Mus. Nat. Hist, vol 1, p. 52, pi. 6, figs. 40-42. 1882. Eynchotiella ricinula Whitfield, Bull. Am. Mus. Nat. Hist vol 1 p. 53, pi. 6, fig. 46. 1883. liynchonella matra Hall, 12th Ann. Rep. Geol. Surv. Ind. p 334, pi. 29, figs. 40-42. 1883. Kynchoitiella ricinula Hall, 12th Ann. Rep. Geol. Surv. Ind. p 330 pi. 29, fig. 46. 1906. Rhynchonella macra Beede, 30th Ann. Rep. Geol. Surv. Ind, p. 1307, pi. 22, figs. 40-42. 1906. Rynchonella ricinula Beede, 30th Ann. Rep. Geol. Surv. Ind., p 1308, pi. 22. fig. 46. 1910. Allorhynchus macra Weller, Bull. Geol. Soc. Am., vol 21, p 509. fig. 9. Description.— ^heW small, compressed, subovate to subtriangular in outline, usually a little wider than long but sometimes longer than wide, especially in small or young individuals, the greatest width anterior to the middle, the postero-lateral margins gently convex or nearly straight and usually meeting at the beak iu an angle of less than 90 degrees, the antero-lateral and anterior margins regularly rounded or with the an- terior margin sometimes straightened. The dimensions of two individuals are: length 6.5 mm. and 5.5 mm., width 7.1 mm. and 6 mm., thickness 3 mm. and 2.7 mm., width of sinus in front 4.5 mm. and 3.1 mm. Pedicle valve most convex posterior to the middle, the surface gently arched from beak to front and also transversely along the line of greatest width, but posteriorly the curvature to the lateral margins is more abrupt, towards the beak the edge of the shell along the postero-lateral margins is abruptly and sharply inflected to form a rather conspicuous pseudo-cardinal area; mesial sinus entirely obsolete posteriorly where it is replaced by a slight mesial elevation which is not differentiated later- ally from the lateral slopes of the valve, towards the front the mesial portion of the valve is somewhat flattened and is rarely slightly de- pressed in a broad, shallow, ill -defined sinus; the beak is pointed, scarcely incurved and is produced posteriorly rather conspicuously in a nearly horizontal direction ; the delthyriura is broadly triangular and is partially closed by deltidial plates which are pierced at the apex by a subelliptical foramen which encroaches to some extent upon the beak of the valve; 200 MISSISSIPPIAN BRACHIOPODA plications simple, roiuided, 14 to 22 in number, two or three of which on each side adjacent to the postero-cardinal margins are very faint, they are obsolete at the beak but originate in the umbonal region, usually at the first strong concentric line of growth. Internally the hinge-teeth are supported by a pair of short dental lamella which do not extend anteriorly beyond the articulation of the hinge. ? ? o C o Fig. 12. — A series of four cross-sections of the rostral portion of the shell of Allorhynchus macra (X 2%), showing the dental lamellae of the pedicle valve and the absence of lamellae in the brachial valve. Brachial valve equally or a little less convex than the pedicle, the greatest convexity posterior to the middle, anteriorly the surface curves gently to the anterior and antero-lateral margins ; posteriorly the surface first curves gently from the median line laterally and then rather abruptly as it approaches the postero-lateral margins ; mesial fold obsolete ; in younger specimens and in the older part of mature ones there is a distinct but slight depression along the median line which continues to the front of full grown examples as a broad mesial flattening which is not sharply differentiated from the lateral slopes of the valve; the beak is rather sharply incurved beneath that of the opposite valve; the plications are entirely similar in form and number to those of the opposite valve. In- ternally the hinge-plate is divided to the base and no median septum is present, anteriorly the two divisions of the hinge-plate are produced as crura. The surface of both valves, in addition to the plications, is marked by exceedingly fine concentric stride and by several stronger lines of growth which are sometimes placed at nearly regular intervals throughout the entire length of the shell, the plications commonly originate .at the first of the lines of growth in front of the beak. Remarks. — This species may be easily recognized by its small size and much compressed shell. The smaller examples may sometimes resemble the, young of the associated Camarotoechia mutata, but that species is apt to have a more pronounced sinus in the anterior margin of the pedicle valve, and the internal characters of the two species are different, the median septum of the brachial valve with its crural cavity sup- porting the bases of the divided hinge-plate being absent in the present species. Khynchonella ricimila Hall, seems to be only the young of the hirger R. macra, and is so considered here, although Whitfield states that mature examples of R. macra do not occur with R. ricinula. In the col- lections from the Salem limestone above Alton, Illinois, the typical locality for R. macra, small examples which seem to agree fully with the figures ALLORHYNCHUS 201 of H, ricinula are not infrequent, and their association is such as to in- dicate that they are without doubt the young of the larger examples which more typically represent R. macra. These two names were both proposed by Hall in the same papei", and as ricinula occurs on an earlier page it might be given priority by some, but as no injustice can be done by adopting macra it seems best to do so since that name was applied to the mature and more normal form of the species. Horizon, Salem limestone. Allobhynchus acutiplicatum n. sp. Plate XXIV, Pigs. 83-86 Description.— Shell small, broadly subovate in outline, broader than long, the greatest width anterior to the mid-iength of the shell, the postero-lateral margins nearly straight and meeting at the beak in an angle of about 90 degrees or a little more, the antero-lateral margins rounded, the anterior margin usually nearly straight but sometimes slight- ly sinuate or a little convex. The dimensions of a perfect specimen are : length of pedicle valve 10.9 mm., length of brachial valve 9.8 mm., greatest width 12.7 mm., thickness 7.2 mm., width of sinus in front 6.9 mm. Pedicle valve convex in the umbonal region, the surface curving abrupt- ly to the postero-lateral margins and a little inflected to the cardinal extremities, from the umbo to the antero-lateral margins the surface is gently convex and from the beak to the anterior margin along the median line it is arched with the strongest curvature anteriorly; the mesial sinus originates near the middle of the valve and becomes rapidly deeper towards the front, where it is a little produced in a broadly rounded extension, its surface is nearly flat transversely in the bottom, with the sides sloping outward; the beak is shai-ply pointed and only a little incurved, being produced posteriorly conspicuously beyond the incurved beak of the opposite valve, with its apex somewhat remote from the umbo of the opposite valve ; the delthyrium broadly triangular, only its basal part filled by the beak of the opposite valve, the remaining portion closed by the deltidial plates which are sometimes destroyed in the fossils ; the plications simple, fine and subangular towards the beak, becoming acutely angular towards the front margin, four usually occupying the sinus, all of which may be included in the bottom of the depression or one may be crowded up a little way upon one of the lateral surfaces, from eight to ten occupy each lateral slope of the valve, growing successively smaller towards the cardinal extremities, the last three or four becoming very faint and sometimes nearly obsolete; the concentric markings of the valve are obscure or nearly obsolete, consisting of a few faint lines of growth which are commonly present near the margin of the valve. Internally the dental plates are well developed and extend one-fourth or a little more of the length of the valve anteriorly from the beak. 202 MISSISSIPPIAN BBACHIOPODA Brachial valve more convex than the pedicle, its greatest convexity near or in front of the middle, the surface curving in nearly a quadrant of a circle from the point of greatest convexity to the beak, with a much gentler curvature to the anterior margin; in the umbonal region the surface is flattened medially and curves abruptly to the postero-lateral margins, from the beak to the antero-lateral margins the curvature of the surface is nearly a semicircle; the mesial fold originating in front of the middle, of only moderate height at the front margin ; the beak strongly incurved beneath that of the opposite valve; the plications are similar in form and number to those of the opposite valve, there being five on the mesial fold and from seven to ten on each lateral slope, towards the outer margin the plications are sharply angular, alternating with those of the opposite valve, and giving to the line of junction between the two valves a strongly zig-zag direction along the anterior and antero-lateral margins; concentric markings similar to those of the opposite valve. Internally the hinge-plate is divided to the apex of the valve and is entirely unsupported, the cardinal process, median septum, and crural cavity wanting. Remarks.— This species differs from A. heteropsis, the genotype, in its finer and more numerous plications, a larger number of which occupy the fold and sinus, in the more arched brachial valve from beak to front, in the less incurved beak of the pedicle valve, and usually in the greater proportional width of the shell. Locality.— V^ing slightly depressed anteriorly and produced in a broad and rather long lingual extension; beak small, pointed, scarcely incurved; the plications strong, mostly simple, rounded or subangular on top, separated by broad rounded furrows of which from 16 to 18 are present upon the valve, about G or 7 occupying the mesial depression near the front of the valve. Tnti r- nally the dental lamellae are well developed and extend anteriorly from the b3ak for nearly one-third the length of the valve with only slight di- vergence, they each join the inner surface of the valve, not being united to form a spondylium elevated upon a median septum. Brachial valve more convex than the pedicle, the greatest convexity towards the front, from this point of greatest convexity the surface slopes to the beak with a long, gentle convex curvature, becoming a little more abrupt near the beak, the anterior slope is much shorter, towards the antero-lateral margins the surface curves much more abruptly, and towards the postero-lateral margins it is abruptly deflected to meet the similar deflected portion of the opposite valve ; mesial fold ill-defined and obscure, not elevated above the general surface of the valve in the pos- terior portion of the valve- but more distinctly elevated in front; beak pointed and incurved beneath that of the opposite valve; plications en- tirely similar to those of the opposite valve. Internally a median septum extends anteriorly from the beak for nearly one-third the length of the valve. The finer surface markings consist of minute, radiating striae, and ex- ceedingly fine concentric markings, in addition to which are occasional stronger, concentric lines of growth, the finer markings usually being visable only with a lens. Remarks. — This species is characterized by its nearly simple plications and its rather broad, triangularly subovate outline. The types of the species are three in number, one nearly complete example with both 208 MISSISSIPPIAN BRACHIOPODA valves present, from a fine grained, compact limestone which resembles, lithologically, bed No. 4 of the Kinderhook at Burlington, Iowa. The other two examples are from the porous brown limestone of bed No. 7 of the same section. In the original description the species is recorded from "the base of the Burlington Limestone," which, from a consideration of the specimens, should doubtless be interpreted as Kinderhook. Girty^ has figured a shell under the name CamaropJioria ringens which is of the type of White 's Bhynchonella caput-testudinis. This shell clearly has the outline suggested by the original definition of E. ringens, and similar specimens have not infrequently been identified with Swallow's species by collectors in the Mississippi Valley, although they commonlj- possess a smaller number of plications than Swallow designates. This type of shell can scarcely be considered as representative of Swallow's species, however, because no example of it has ever been observed by i-e- cent collectors in the cherts from which 7v'. ringens is said to have been collected. Horizon. — Kinderhook. Rhynchotetra ovATUM (Gregcr) Plate XXVII, Figs. 16-20 1910. Paraphorhynchus ovatum Greger, Am. Jour. Sci. (4), vol. 29, p. 74, figs. 9-10. Description.— 'SheW of medium size or somewhat larger, subovate in outline, longer than wide, the greatest width near the mid-length, the posterior extremity iisually acutely pointed, the line of junction between the valves deeply and strongly serrate. The dimensions of a nearly per- fect specimen, one of the cotypes, are : length of pedicle valve 35.5 mm., length of brachial valve 33.3 mm., greatest width 26.8 mm., thickness 18 mm. Pedicle valve gently convex throughout the greater portion of its sur- face, its greatest depth near the middle, abruptly deflected towards the opposite valve near the postero-lateral margins, the deflected surface nearly flat and lying nearly at a right angle to the plane of the valves or slightly concave and somewhat inflected to the margin towards the cardinal extremities; mesial sinus obscure or essentially obsolete, when best develoved it is broad, only slightly depressed, and restricted to the extreme anterior part of the valve; beak not prominent, pointed, only moderately incurved; surface of the valve marked by from sixteen to twenty, usually simple, strong but rather low, radiating plications, rounded on top and separated by rounded furrows, most of them orig- inate near the beak, only rarely and upon some specimens never do they increase by division or implantation upon the body of the valve. iMon. U. S. Geol. Survey, vol. 33, pt. 2, pi. 69, figs, lab (1889). RHYNCHOTETRA 209 Brachial valve slightly deeper than the pedicle but similar in form, it is gently convex through the greater portion of its surface, being abruptly deflected towards the opposite valve near the postero-lateral margins, the deflected portion is a little broader than that of the opposite valve and is continuous with it, the two together forming the subovate, flattened or slightly concave lateral areas in the posterior portion of the shell; mesial fold obscure or obsolete, when best developed it is but slightly diflierentiated and is restricted to the extreme anterior portion of the valve ; beak pointed, incurved beneath that of the opposite valve ; plications similar in all respects to those of the opposite valve. Surlac':' of both valves, when well preserved, marked by fine, radiating striae, about three or four of which occupy the space of one millimeter. Eemarks. — The internal characters of this species have not been fully investigated, but the strong dental lamellae of the pedicle valve joining to form a spondyliura-like cavity near the inner surface of the valve, are clearly visible in one example with the rostral portion of that valve broken, and in the brachial valve a well developed median septum is clearly seen upon the slightly weathered surface. There is no reason to doubt but that the arrangement of the internal lamellae agrees essentially \\ith that of E. missmiriensis, which has been carefully sectioned. The species agrees most closely with R. caput-testudinis, but it is somewhat smaller, with much less convex valves, with a more subovate outline and somewhat finer plications. It is clearly distinct from E. gibhosum by reason of its less convex valves and its simple plications which usually originate near the beak and continue to the margin without additions by subdivision or intercalation. Horizon. — Choutenu limestone. Rhynchotetra elongatum n. sp. Plate XXVIII, Figs. 9-12 , Description. — Shell below medium size, longer than wide, the greatest width in front of the middle, the anterior portion of the shell sub- semicircular in outline, the posterior poi'tion acutely subcuneate. The dimensions of a nearlj' perfect individual are : length of pedicle valve 27.2 mm., length of brachial valve 26.5 mm., width 18 mm., thickness 8.5 mm. Pedicle valve depressed convex, greatest convexity posterior to the middle, nearly flat antei'ior to the middle, the postero-lateral margins abruptly deflected towai-ds the opposite valve, the deflected portion on each side forming one-half of a suboval, flattened or concave region on each side of the beak ; mesial sinus essentially obsolete ; beak small, pointed, scarcely incurved; the umbonal region with a median septum internally; plications nine or ten in number, those in the middle of the 210 MISSISSIPPIAN BRACHIOPODA shell strong, 'becoming much fainter towards the postero-lateral margins, mostly simple, and becoming obsolete near the beak where the umbonal region for a short distance is essentially nonplicate, the plications are subangular on top and are separated by broad furrows. Brachial valve depressed convex, similar in form to the pedicle, the surface gently arched from the beak to the anterior and antero-lateral margins, not so much flattened anteriorly as the opposite valve, the postero-lateral margins abruptly deflected to meet the similar deflected portions of the opposite valve and to form a part of the subovate flattened regions on each side of the beak; mesial fold obsolete; beak small, pointed, incui"ved beneath that of the opposite valve; plications entirely similar to those of the opposite valve. The minute surface markings consist of extremely fine, radiating striffi. Lines of growth of varying strength occur at intervals. Remarks.— This shell is allied to K. caput -tcstudims, but it differs from that species in its much smaller size and less convex valves. These char- acters might be interpreted as youthful characters, but the type specimen has all the appearances of being a mature shell. The species also differs from E. gibiosiim in its smaller size and in the absence of the conspicuous divarication of the plications. It is perhaps most closely allied to E. ovatum, but it is nari'ower, much miore elongate, and proportionally thinner. Horizon. — Pierson limestone of the Kinderhook. Rhtnchotktka missoueiensis n. sp. Plate XXVIII, Figs. 1-8 Description.— Shell of about medium size, triangularly subovate in out- line, longer than wide, the greatest width anterior to the middle, the postero-lateral margins nearly straight or a little concave, the antero- lateral margins rounded, the anterior margin gently convex or sometimes subtruncate. The dimensions of a nearly complete specimen are : length of pedicle valve 29 mm., length of brachial valve 27.5 mm., width 27 mm., thickness 15.7 mm. Pedicle valve depressed convex, the surface gently and nearly regularly convex longitudinally from beak to front, and also transversely along the line of maximum width ; along the postero-lateral margins the valve is abruptly deflected towards the opposite valve to form a minor portion of the suboval, flattened or somewhat concave, lateral regions lying upon each side of the beak ; mesial sinus obsolete ; beak small, pointed, only slightly incurved ; plications broad, rounded, separated by rounded fur- rows about equal to the plications in width ; about four or five plications originate at the beak, the two lateral ones each giving origin to three or four others from their outer sides, the median ones usually bifurcating RHYNCHOTKTRA 211 once near or in front of the middle, making twelve to fifteen plications in all upon the lateral and anterior margins ; internally the dental lamel- lae are strongly developed and are joined to form a spondylium supported by a median septum, as has been shown in the generic description. Brachial valve more convex and deeper than the pedicle, the greatest depth near the middle, the surface curving from the central point with a regular convexity in all directions; along the postero-lateral margins the surface is abruptly deflected towards the opposite valve, the deflected portion forming the larger part of the flattened or concave areas on each side of the beak ; mesial fold obsolete ; the beak small, pointed, incurved beneath that of the opposite valve ; the plications entirely similar to those of the opposite valve, but with the later ones added by intercalation rather than by division. Internally, a median septum is present which is divided internallj^ to form a crural cavity, as has been shown in the generic description. The minute surface markings consist of fine, radiating strife. Lines of growth of varying strength may be present and are sometimes a little crowded towards the anterior margin. Remarks.— This species most closely resembles B. gibbosum, but it is a much thinner species, with much less convex valves, and with the great- est width more anterior in position ; in the form and arrangement of the plications, however, the two species are much alike. Horizon. — Burlington limestone. Rhynchotbtra gibbosum (Greger) Plate XXVII, Pigs. 7-15 1894. Ehynchonella sp. ( ?) Keyes, Mo. Geol. Surv., vol. 5, pi. 41, fig. 8. 1910. Paraphorhynchvs gibbosum Greger, Am. Jour. Sci. (4), vol. 29, p. 73, figs. 1-6. Description.— Shell strongly plicate, of medium size or larger, longer than wide, the greatest width near or in front of the middle, the anterior outline usually subsemieircular, the posterior outline acutely subcuneate. The dimensions of a nearly complete specimen, a cotype, are: length 39 mm., width 25.5 mm., thickness 28 mm. Pedicle valve arched from the beak to the front, but somewhat more flattened posteriorly, arched to the antero-lateral margins, the postero- lateral margins abruptly deflected towards the opposite valve, the de- flected portion forming nearly one-half of an oval, flattened or concave lateral region upon each side of the shell; mesial sinus obsolete in the posterior portion of the shell, broad, shallow, obscure and ill-defined anteriorly; beak small, pointed, a little incurved; plications strong, rounded on top, separated by broad, rounded furrows, from three to five originate near the beak, all or nearly all of which divide at intervals 212 MISSISSIPPIAN BRACHIOPODA in passing from the beak to the front margin, the one on each side nearest to the postero-lateral deflection of the valve giving origin to four or more plications from its outer side which ai'e arched across the oval, postero-lateral flattened portion of the valve. Brachial valve more convex than the pedicle, arched from the beak to the anterior and antero-lateral margins, the greatest depth of the valve near the middle, the postero-lateral margins sharply deflected to meet the similar deflected portion of the opposite valve and helping to form the oval, flattened areas on each side the rostral portion of the shell; mesial fold obsolete posteriorly, obscure and poorly defined an- teriorly; beak small, pointed, incurved beneath that of the opposite valve; plications similar to those of the opposite valve, but with the younger plications often added by intercalation instead of by bifurcation ; at the postero-lateral margins plications similar to those of the opposite valve are arched across the deflected portion of the valve. The minute surface markings of the shell consist of exceedingly fine radiating stria? which are crossed by fine concentric lines of growth. Stronger lines of growth are sometimes present at intervals, more es- pecially towards the anterior margin. Remarks.— In general form, size and proportions this species resembles />'. caput-testudinis, but it differs from that species iri being notably thicker and especially in the conspicuous and more or less frequent bifurcation or intercalation of plications; the presence of the strong plications which arch across the oval postero-lateral regions of the shell also distinguishes this species from K. caput-testudinis. ffomon.— Burlington limestone. Genus TETRACAMERA Weller Description.— ^he]l rhynchonelliform, small or of medium size, triangu- larly subovate to subpentagonal in outline, the mesial fold and sinus poorly developed or nearly obsolete except towards the front, the lateral and anterior margins of both valves deflected so as to stand at nearly right angles to the plane of the valves, both valves marked by simple, subangular or rounded plications which reach to the beak. Internally the pedicle valve possesses strongly developed dental lamellae which curve towards the median line as they approach the floor of the valve, and form a deep spondylium which rests upon the inner surface of the valve or is slightly raised on a median septum anteriorly, from the ex- ternal surface of each dental lamella a transverse buttress plate extends across the intervening cavity to the inner surface of the outer shell wall. In the rostral portion of the brachial valve a strong median septum is present which is undivided at the apex of the valve, but before the articulation of the shell is reached a median incision is formed internally TETRACAMERA 213 which is at first arehed over but soon becomes open internally by the in- cision between the lateral divisions of the divided hinge-plate, the crural cavity so formed being: essentially identical with that of Camarotcechia; the cavities between the median septum and the outer shell walls are each divided by a lamella or septum resting upon the floor of the valve and supporting the inner margin of the corresponding lateral division of the hinge-plate, these lateral septa extending farther anteriorly than the median septum. ^8 V^yS* J Fig. 16. — A series of ten cross-sections of the rostral portion of the shell of Tetracamera subcuneata (X 2%), showing the dental lamellae and buttress plates of the pedicle valve, and the median and two lateral lamellae, the crural cavity and crura of the brachial valve. Remarks.— The species included in this genus were referred to Cam- arophoria by Hall and Clarke,^ and usually have been so referred since the publication of their work. The shells do not possess the character- istic cruralium of Camarophoria, besides possessing other characters wholly foreign to that genus. The most essential generic characters are the presence of the buttress plates connecting the dental lanielhe with the inner surface of the outer shell wall, and the presence of the supple- mentary lamellai in the rostral portion of the brachial valve in addition to the median septum. The species T. subtrigona which is here included in the genus difi'ers in a rather fundamental mainner from the genotype, not only in the general form of the shell but in the arrangement of the internal lamella', and should perhaps be made the type of a distinct genus, but the discussion of these characters is reserved for treatment under the specific description. 1 Pal. N. Y., vol. 8, pt. 2, p. 214 (1894). 214 MISSISSIPPIAN BRACIIIOPODA Tethacamera subcuneata (Hall) Plate XXVIII, Figs. 13-24 1856. Rhynchonella subcuneata Hall, Trans. Albany Inst., vol. 4, p. 11- 1858. Rhynchonella subcuneata Hall, Geol. Iowa, vol. 1, pt. 2, p. 658, pi. 23, figs. 3a-c. 1863. Bhynchonella perrostellata Swallow, Trans. St. Louis Acad. Sci., vol. 2, p. 85. 1882. Rhynchonella siCbcuneata Wliitf., Bull. Am. Mus. Nat. Hist., vol. 1, p. 51, pi. 6, figs. 47-49. 1883. Rhynchonella subcuneata Hall, 12tli Rep. Geol. Surv. Ind., p. 333, pi. 29, figs. 47-49. 1894. Camarophoria subcuneata Hall and Clarke, Int. to Study of Brach., pt. 2, pi. 45, figs. 3-4. 1894. Rhynchonella subcuneata Keyes, Mo. Geol. Surv., vol. 5, p. 102. 1895. Camarophoria subcuneata Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, pi. 62, figs. 34-37. 1906. Camarophoria suhcuneata Beede, 30th Ann. Rep. Geol. Surv. Ind., p. 1304, pi. 22, figs. 47-49. 1910. Tetracamera subcuneata Weller, Bull. Geol. Soc. Am., vol. 21, p. 503, fig. 4. Description.— 8he\l below mediiim size, the valves subequally convex, subtriangular in outline, usually broader than long, the greatest width uear the anterior extremity, the long postero-lateral margins straight or a little concave, usually meeting at the beak in an acute angle. The dimen- sions of two examples are : length 11.7 mm. and 10.4 mm., width 12 mm. and 11.5 mm., thickness 7.3 mm. and 6.3 mm. The dimension of the largest example observed are : length 15.3 mm., width 15.3 mm., thickness 9.6 mm. Pedicle valve depressed-convex, the surface gently arched from the beak to the anterior margin except in old shells in which the valve is rather abruptly deflected anteriorly to meet a similar deflection of the opposite valve, along the postero-lateral margin the valve is abruptly deflected towards the opposite valve, the deflected portion on each side forming about one-half of a smooth, flattened or slightly concave region on each side of the beak; mesial sinus obsolete posteriorly and repre- sented anteriorly only as a slight,, indefinite flattening of the valve which sometimes cannot be detected at all ; beak small, sharply pointed, slightly incurved, the delthyrium triangular, open towards the apex but closed below by the beak of the opposite valve; plications angular, from 12 to 20 in number, either simple or dividing near the beak, in no case is the bifurcation upon the body of the shell a conspicuous feature. Brachial valve similar in form to the pedicle, the surface arched from the beak to the anterior margin, the curvature being strongest near the beak, the postero-lateral margins deflected to meet the similar de- flected portion of the opposite valve and to take part in the formation TETRACAMERA 215 of the flattened or concave lateral regions on each side of the beak; mesial fold obsolete ; beak strongly incurved and partially filling the del- thyrium of the opposite valve ; plications entirely similar to those of the opposite valve. The minute surface markings consist of fine, obscure, radiating strise which are usually obsolete because of the condition of presers'ation of the shell surface, when preserved they can be best seen upon the flattened, postero-lateral portions of the shell. Pine concentric lines of growth are present when the shell is properly preserved, and are subimbricating in character, stronger lines of growth occur at irregular intervals. In old shells which are much flattened anteriorly by reason of the anterior deflection of the valves, and to a less extent in younger individuals, the margins of the valves are deeply incised by the interlocking serrations of the two valves, and parallel with the line of juncture and adjacent to it the lines of growth are usually conspicuously crowded. Bemarhs. — This species is a highly characteristic member of the fauna of the Salem limestone. Its only close ally is T. arctirostrata, which is char- acterized by its larger size and by the presence of fine radiating striaj upon the surface of the shell. Horizon.— Salem limestone. Tetracamera arctirostrata (Swallow) Plate XXVIII, Figs. 25-34 1863. Rhynchonella arctirostrata Swallow, Trans. St. Louis Acad. Sci., vol. 2, p. 84. 1910. CanM,rophoria arctirostrata Greger, Am. .Jour. Sci. (41, vol. 29, p. 73, figs. n-12. Description.— '&\iQ\\ below medium size, length and width sub-equal or somewhat wider than long, the greatest width in front of the middle, subtriangular in outline with the postero-lateral margins long and nearly straight, the antero-lateral margins rounded, the anterior margin some- what truncated or slightly convex, the line of junction between the valves deeply and sharply serrate. The dimensions of a very perfect example are: length of pedicle valve 15.6 mm., length of brachial valve 14.8 mm., greatest width 15.4 mm., thickness 12.8 mm. Pedicle valve gently convex throughout the greater portion of its surface and gently arched from the beak to near the front margin, to- wards the postero-lateral margins the valve is abruptly deflected to the margin, the deflected portion lying in nearly a right angle to the plane of the valve, antero-laterally the deflection is only a little less abrupt but anteriorly it is notably less, although this margin also curves towards the opposite valve until it lies nearly at right angles to the plane of the valve; mesial sinus obscure, sometimes nearly obsolete, when best de- veloped it is broad and only slightly depressed and is restricted to the 216 MISSISSIPPIAN BBACHIOPODA anterior portion of the valve; beak acutely pointed and moderately in- curved; plications sixteen to twenty in nuinl)er, simple and reaching from the beak to the margins without intercalations, rounded posteriorly but becoming more or less subangular near the anterior and antero- lateral margins, those upon the postero-lateral deflections of the valve curving strongly towards the margin. Brachial valve much deeper than the pedicle, its greatest depth near the anterior margin, gently convex along the median line from the point of greatest depth to the beak and curving abruptly from the same point to the anterior margin, gently convex transversely across the central portion of the valve and abruptly deflected laterally towards the opposite valve, postero-laterally the deflected portion is a little concave, becoming a little convex anteriorly, the deflected portion being much broader than the similar deflected portion of the opposite valve ; mesial fold not dif- ferentiated from the general curvature of the valve except in the sinuosity of the anterior line of junction of the two valves; the beak pointed and incurved beneath that of the opposite valve; plications similar in form and number to those of the opposite valve. Surface of both valves marked by fine, regular, concentric lines of growth which follow the direction of the serrate margin, upon the older portion of the shell they are commonly obliterated, even upon the best preserved specimens, but towards the margin they are clearly defined unless the surface is exfoliated, a few stronger lines of growth are usually present at irregular intervals, or they may be entirely absent ; besides the concentric lines the surface is marked by exceedingly fine radiating striiE which are best observed only upon the postero-lateral deflected portions of the valves, and are entirely obliterated upon exfoliated shells. Eemarhs. — The internal characters of representative examples of this species have not been carefully examined because of the lack of material, but enough has been seen to show that these structures are essentially identical with those of T. suhcuneata. Indeed the whole aspect of a good example of the species is that of a rather large specimen of T, suhcwieata, and it is perhaps ill-advised to consider these two species as distinct. If T, arctirostrata is a good species it mixst rest upon its larger .size, deeper brachial valve, and especially upon the fine radiating COStffi. Homo??.— Salem limestone. Tetracamera missouriensis n. sp. Plate XXVIII, Figs. 35-39 Description. — Shell of medium size or usually somewhat smaller, trian- gularly subovate in outline, the greate.st width anterior to the middle, usually longer than wide, the long postero-lateral margins nearly straight TETBACAMEBA 217 aud meeting at the beak in an acute angle, the anterior and antero-lateral margins subsemicircular, the line of junction between the two valves deeply and sharply serrate, especially along the anterior and antero-lat- eral margins. The dimensions of an internal cast of a pedicle valve are : length 22.9 mm., greatest width 20 ram., convexity 4.8 mm. The dimen- sions of an internal cast of a brachial valve are: length 22.7 mm., width 19.4 mm., convexity 8 mm. Pedicle valve nearly flat throughout the greater portion of its surface, gently convex in the umboual region, abruptly deflected along its postero- lateral margins and only a little less abruptly deflected along the anterior and antero-lateral margins; mesial sinus essentially obsolete or repre- sented only by a slight simiosity of the margin upon the anterior deflected portion of the valve ; beak acutely pointed, only moderately incurved ; plications twenty to twenty-six in number, rounded or subangular, usually simple and extending from the beak to the margin, but occasionally with one or two intercalated plications anterior to the beak, the plications be- coming successively smaller towards the postero lateral margins, those upon the deflected postero-lateral surfaces of the valve curving rather strongly towards the margin. Internally the dental plates are well de- veloped and are joined near the inner surface of the valve to form a spon- dylium which is supported by a well defined median septum which reaches anteriorly about one-third the length of the valve, from the outer surface of each dental lamellse a lateral buttress plate passes to the inner surface of the postero-lateral deflected portion of the valve, the buttress plates extending anteriorly from the beak for about one-third the length of the median septum. Brachial valve similar in contour to the pedicle, with the postero-lateral surfaces abruptly deflected to meet the similarly deflected portions of the opposite valve, and the anterior and antero-lateral margins also deflected in a manner similar to that of the opposite valve, the non-deflected sur- face of the valve somewhat more convex than that of the pedicle valve, and the depth of the valve a little greater ; mesial fold obsolete except for the slight sinuosity in the anterior margin ; the beak acutely angular and incurved beneath that of the opposite valve; plications similar in form and number to those of the pedicle valve. Internally the median septum extends anteriorly from the beak for from one-third to nearly one-half the length of the valve, the lateral lamella which support the inner mar- gins of the divided hinge-plate join the inner surface of the valve at the base of the median septum so that the three lamellaa make but a single median slit in the internal casts of the valve. The minute surface markings not preserved upon the internal casts, to which observations were limited. 218 MISSISSIPPLVN BRACmOPODA Remarks. — ^The specimens here described occur commonly in the cherts of Callaway County, Missouri, the locality and horizon of the type of the species described by Swallow as lihynclionella ringens, and they conform in general outline with the shell suggested by the original definition of that species. However, no examples have been observed by the writer to attain more than about one-half the size of Swallow's type and none of the specimens exhibit a distinct mesial sinus, which, in the original defini- tion of the species, is said to be broad and shallow ; furthermore, the plica- tions are more numerous. If the shell here defined should ever attain so large a size as is indicated by Swallow, it is not improbable that a shallow mesial sinus might be developed, but the number of plications ought to be somewhat greater in the larger example rather than smaller. How- ever, if this shell does not belong to Swallow's species, and it is believed that it does not, it must be an undeseribed form. The species mast closely resembles T. arctirostrata, but it is a larger and more elongate shell, and in the specimens observed, lacks a mesial depression in the anterior portion of the pedicle valve. The species may further be differentiated by reason of the occasional intercalation of plications, in some specimens, which has not been observed in T. arctirostrata. Locality.— Cailnway County, Missouri (residual chert). Tetracamera subtrigona (Meek and Worthen) Plate XXIX, Figs. 1-13 1860. BhyncJionella suhtrigona. Meek and Worthen, Proc. Acad. Nat. Sci. Phil., p. 451. 1860. Bhynchonella Parvini McChesuey. Desc. New Foss., pt. 2, p. 83. 1865. Bhynchonella Parvini McChesney, Plates 111. New Spec. Foss., pi. 6, figs. 2a-b. 1866. Camarophorkb suhtrigona Meek and "Worthen, Geol. Surv. 111., vol. 2, p. 251, pi. 18, figs. 7a-c. 1868. Camarophoria subtrigona McChesney, Trans. Chicago Acad. Sci., vol. 1, p. 31, pi. 6, figs. 2a-b. 1894. Camarophoria suhtrigona Hall and Clarke, Int. to Study of Brach., pt. 2, pi. 45, figs. 1-2. 1894. Rhynchomella subtrigona Keyes, Mo. Geol. Surv., vol. 5, p. 102. 1895. Camarophoria subtrigona Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, pi. 62, figs. 38-43. 1895. Camarophoria ringens Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, pi. 84, fig. 45. 1910. Camarophoria ringens Gi*eger, Am. Jour. Sci. (4), vol. 29, p. 71, figs. 7-8. 1910. Tetracamera suhtrigona Weller, Bull. Geol. Soc. Am., vol. 21, p. 504, fig. 5. Description. — Shell of medium size or larger, broadly subtriangular or subpentagonal in outline, wider than long, truncated in front, with broad, TETRACAMERA 219 simple plications. The dimensions of a nearly complete but somewhat distorted individual are : length 32.5 mm., width 37 mm., thickness 27 mm. Pedicle valve flattened on the umbo and in front of the umbo, gently convex from the beak to the front in the median portion, abruptly de- flected near the margin, the front of the shell being nearly at right angle to the flattened umbonal region, towards the antero-lateral margins the surface is at first elevated by a gentle concavity and is then abruptly de- flected towards the opposite valve forming a sort of angular crest along each antero-lateral margin, the postero-lateral margins are nearly straight and meet at the beak at an obtuse angle of about 110 degrees, along these margins the surface is abruptly bent towards the opposite valve, and is usually somewhat inflected forming with a similar area on the opposite valve, an obscurely plicated, flattened or concave area on each side of the beak; mesial sinus broad, shallow, ill-defined, becoming somewhat deeper anteriorly; the beak small, pointed and moderately incurved; the plica- tions are strong, simple, rounded or a little subangular, and are separated by more angular furrows, from 14 to 20 are present on the valve, several O^^TOTO Fig. 17. — A series of sixteen cross-sections of the rostral portion of the shell of Tetracamera subtrigona (X 1%), showing the characters of the internal lamellae. next the postero-lateral margins often being faint or nearly obsolete, about six or seven occupy the mesial simis, the margin of the valve is deeply and acutely serrate, the projections being opposite the furrows between the plications, the deepest and strongest serrations are in the front of the shell, on each side they decrease in strength with the weaken- ing of the plications. Internally a strong median septum extends from the beak nearly to the line of deflection of the valve near its anterior 220 MISSISSIPPIAN BRACHIOPODA margin and is often more or less abruptly thickened near its anterior ex- tremity, this septum supports a spondylium whose spreading sides meet at an angle in the bottom. Brachial valve much deeper than the pedicle, the greatest depth near the front margin ; ' from this point the surface slopes with a gentle convex curvature to the beak, and is abruptly deflected to the anterior and antero-lateral margins, along the postero-lateral margins the surface is abruptly bent towards the opposite valve and is usually somewhat inflected and forms more than one-half of the smooth, oval, concave areas on each side of the beak ; mesial fold obsolete posteriorly, broad and ill-defined anteriorly; the beak is strongly incurved beneath that of the opposite valve and partly fills the delthyrium of that valve, the plications are similar to those of the opposite valve and are alternate with them, as are the serrations on the margin, the plications towards the postero-lateral margins are strongly arched. Internally the valve bears a strong median septum which extends from the beak more than half way to the line of deflection of the valve towards its anterior margin, in its anterior half this median septum bisects a subovate or subelliptical mus- cular impression, at the beak of the valve it supports a subquadrangular, spoon-shaped hinge-plate whose ventral surface is depressed medially through about one-third its width, the lateral margins of this depressed region diverge from a point at the beak and are overhanging so as to give to the depressed region the appearance of a flattened, conical tube cleft along one side. In addition to the plications each valve is marked only by concentric lines of growth which are obscure or obsolete over the greater portion of the shell, ordinarily being clearly recognizable only upon the deflected portion of the valves near the anterior margin. h'cmarks. — This species has been most commonly recognized in the re- sidual cherts of the Keokuk limestone, where it occurs in the condition of internal easts showing clearly the median septum in each valve and the muscular impressions of the brachial valve. Where it has been found in situ it is known only in the Keokuk limestone. Hall and Clarke^ have illustrated an internal cast under the name Camaroplwria ring ens Swallow, which is clearly an example of Meek and Worthen's Rhynchonella svb- trigona, and more recently a specimen of the .same species has been figured by Greger^ as typical of Swallow's species. Swallow's type has been de- stroyed but the specimen illustrated by Greger is said to bear a label writ- ten by Swallow himself and is therefore considered by that writer to be authentic, a conclusion which, if true, would necessitate Swallow's name taking precedence over that of Meek and Worthen. A careful examina- 1 Pal. N. Y., vol. 8, pt. 2, pi. 84, fig. 45. (1895.) 2 Am. Jour. Scl. (4), vol. 29, p. 71. figs. 7-8. (1910.) SHUMARDEIiLA 221 tion of a score or more of good examples of Meek and Worthen 's species, in comparison with Swallow's original definition of li. ringens, brings out the fact that they are always very different in outline from the shell in- dicated by Swallow. R. subtrigona is always notably broader than long, while R. ringens is distinctly defined as being longer than broad. The species is a close ally of the rare R. isorhyncha M'Coy, from the Mountain Limestone fauna of Ireland, but the American species is much broader than the Irish form with more conspicuously deflected anterior and antero- lateral margins. The crest-like elevation of the antero-lateral margins of the pedicle valve of C. subtrigotia is also lacking in C. isorhxjncha. The internal characters of this shell differ somewhat notably from those of the genotype of Tetracamera. The characteristic buttress plates are present in the pedicle valve, but the arrangement of the lamelhe in the rostral portion of the brachial valve is quite different. These differences may be best comprehended through a comparison of the sections which are given of the two species. It is possible that this species should properly be recognized as a member of a distinct genus, but for the present it seems best to consider it as congeneric with T. suicuneata. Horizon. — Keokuk limestone. Genus SHUMARDELLA Weller Description. — Shell rhynchonelliform, usually below medium size, sub- ovate to subpentagonal in outline, often subglobular in form, the mesial fold and sinus well developed anteriorly, the anterior margin of the sinus much produced; the surface marked by broad, low, rounded or subangu- lar plications which are more strongly defined on the fold and sinus, and which may be nearly obsolete. Internally the dental lamella of the pedicle valve are well developed. In the brachial valve a strong median septum is present and is divided internally to form a narrow and deep crural cavity which is closed on its cardinal side, this closure being con- tinuous to beyond the point where the median septum is joined to the hinge-plate, the lateral walls of the crural cavity being suspended in the cavity of the valve for a short distance beyond the point where they are connected with the median septum. The crura are formed by the an- terior extension of the walls of the crural cavity where they are joined to the hinge-plate. Remarks. — This genus is characterized by the obsolescent plications of the shell and by the crural cavity which is short in an autero-posterior direction and entirely closed on its cardinal side. 222 MISSISSIPPIAN BRACHIOPODA Shumardella missouriensis (Shumard) Plate XXV, Figs 43-52 1855. Rhynchonella Missouriensis Shumard, Geol. Rep. Mo., p. 204, pi. C, figs. 5a-c. 1894. Ehynchonella missouriensis Keyes, Mo. Geol. Surv., vol. 5, p. 100. 1910. Shumardella missouriensis Weller, Bull, Geol. Soe. Am., vol. 21, p. 512, fig. 14. Description.— Shell below medium size, triangularly subovate in outline, usually wider than long, the greatest width anterior to the mid-length, the postero-lateral margins nearly straight, meeting at the beak in an angle of about 100 degrees, the antero-lateral margins rounded, the an- terior margin nearly straight or slightly emarginate. The dimensions of two nearly perfect specimens are : length 20 mm. and 18 ram., width 22.4 mm. and 17.9 mm., thickness 16.5 mm. and 15 mm., width of sinus in front 16 mm. and 14.8 mm. Pedicle valve very shallow, the umbo narrowly convex, usually with a small concave region on either side, beyond which a narrow margin, be- coming abruptly wider towards the beak, is sharply inflected, towards the antero-lateral margins the surface is nearly flat or slightly convex, and from the beak to the front along the median line it is strongly but not regularly arched; the mesial sinus originates posterior to the middle of the valve, it is broad and of moderate depth with the surface rather ab- 8 88 8 Fig. 18. — A series of nine cross-sections of tlie rostral portion of the shell of Shumardella missouriensis (X 2%), showing the dental lamellse of the pedicle valve, the hinge-plate, median septum, crural cavity, and crura of the brachial valve. ruptly curved towards the opposite valve anteriorly and produced into a broad, lingual extension at nearly a right angle to the plane of the valve, it is coarsely serrate on the front margin ; beak small, pointed, moderately incurved ; the delthyrium nearly filled by the beak of the opposite valve, SHUMARDELLA 223 the deltidial plates not observed; plications few in number, broad, low, rounded, two, or more rarely three, originating on or just in front of the umbonal region and occupy the bottom of the sinus, on each lateral slope of the valve two plications are usually present which are fainter than those of the sinus and originate closer to the margin. Internally the teeth are supported by a pair of dental plates which quickly become obsolete in front of the articulation of the hinge. Brachial valve gibbous, the greatest depth near the front margin in adult examples, the surface usually slopes along the median line from the point of greatest convexity to the beak with a nearly regular curvature, becoming a little more convex near the beak, anteriorly there is often a short but somewhat abrupt slope to the margin, towards the lateral mar- gins the surface curves at first gently and then more abruptly from the median line, and towards the beak on either side there is a distinct and sometimes rather deep lateral concave region ; mesial fold scarcely or not at all differentiated in the posterior half of the valve, usually becoming more prominent anteriorly; beak incurved beneath that of the opposite valve ; plications similar in form and number to those of the opposite valve, the three or rarely four of the mesial fold alternate with those of the sinus and are the strongest ones on the valves, those of the lateral slopes often nearly or quite obsolete. Internally there is no cardinal pro- cess, a thin and rather short median septum is present supporting the in- itial portion of the hinge-plate, at the apex of the beak this septum is not divided but anteriorly it is split into two parts, one of which supports each side of the hinge-plate, but the base of the hinge-plate is solid and roofs over the cavity between the two divisions of the septa, so that they do not form an open crural cavity such as is present in the genus CamarotoBchia, anteriorlj' the hinge-plate is divided and at the point of articulation of the hinge the two divisions are separate and the median septum is so much reduced that it no longer supports them. The crura ex- tend from the anterior extremities of the divided hinge-plate into the cavity of the shell. The surface of both valves is marked by fine, regular, concentric striae, and iisually by several stronger, irregularly developed, concentric lines of growth towards the front. Remarks. — This species has been frequently misinterpreted. Every published illustration to which the name has been applied, save only the original one by Shumard, is incorrectly identified, and even this author has represented two different species. The name missotmensis is here re- tained for the larger form illustrated by Shumard, and the one with which his description more fully agrees. The species is restricted to the Chouteau limestone fauna and is most commonly represented in the typi- cal Chouteau limestone in central Missouri. 224 MISSISSIPPIAK BRACIIIOPODA The later authors who have referred to the species have placed it in the geims Pugnax, but the distinct median septum of the brachial valve, which is divided above for the support of the hinge-plate is entirely different from those characters in Pvgnax. It differs from Caniarotopxhia in the arching over of the cavity between the divisions of the median septum by the un- divided basal portion of the hinge-plate, and by the consequent absence of the open crural cavity at the base of the hinge-plate. These internal char- acters, as well as the external aspect of the shell, distinguish the species from any of the recognized generic divisions of rhynchonelloid shells and it is in consequence made the type of a new genus. Horizan. — Chouteau limestone. Shumardella obsolens (Hall) Plate XXVI, Pigs. 1-9 1855. KhyncJionella obscura-plicata Shumard, I and II, Rep. Geol. Surv. Mo., p. 218. (Name only.) 1855. Khynchonella Missouriensis Shumard. I and II Rep. Geol. Surv. Mo., p. 204, pi. C, fig. 5a (not figs. 5b-c). 1860. Khijnchonella {Eatonia) ohsolens Hall, 13th Rep. X. Y. State Cab. Nat. Hist., p. 111. 1866. Khynchonella missouriensis Meek and Worthen, Geol. Surv. 111., vol. 2, p. 153, pi. 14, figs. 4a-b. 1910. Shumardella obsolescens Weller, Bull. Geol. Soe. Am., vol. 21, p. 513, fig. 15. Description.— Shell below medium size, nearly smooth, subglobular in form, wider than long, the greatest width near the mid-length, posterior lateral margins meeting at the beak in an obtuse angle, the lateral mar- gins rounded, the anterior margin emarginate. The dimensions of two perfect specimens are : length 15.9 mm. and 14.4 mm., width 16.7 mm. and 16.4 mm., thickness 13.7 mm. and 12.8 mm., width of sinus in front 11 mm. and 9.5 mm. Pedicle valve shallow, convex on the umbo, the surface gently convex from the umbo to the antero-lateral margins, curving strongly to the postero-lateral margins, the curvature becoming more abrupt towards the beak, from the beak to the front margin along the median line the curvature of the surface is a subsemicircle ; mesial sinus obsolete in the umbonal region, originating as a broad, shallow, rounded depression post- erior to the middle of the shell and becoming rapidly deeper anteriorly, in front it is produced in a broad, elongate, terminally rounded lingual extension which retains its concavity to the end giving to the shell its emarginate outline in front; beak small, incurved, nearly in contact with the umbo of the opposite valve ; the delthyrium nearly filled by the beak of the opposite valve, the deltidial plates obscure and not observed in any of the specimens studied, the foramen small ; plications nearly obso- SHUMARDELLA 225 lete, from two to five, more usually two or three, originate on or in front of the umbonal region and pass to the anterior margin along the bottom of the sinus, these plications are low and rounded, somewhat variable in strength but always comparatively faint, upon the lateral slopes of 0 G Fig. 19. — A series of eight cross-sections of the rostral portion of the shell of Shumardella ohsolens (X 2%), showing the internal characters. the valve the plications are obsolete. Internally the hinge-teeth are supported by short dental plates w-hich scarcely extend beyond the articu- lation of the hinge. Brachial valve gibbous, the iimbonal region protuberant, sometimes extending nearly as far as the beak of the opposite valve, the greatest convexity near the anterior margin, the surface strongly convex from beak to front along the median line, and much more stronglj- convex transversely, towards the beak the surface on each side is a little in- flected to form, with a similar inflected portion of the opposite valve, a small, more or less conspicuous concave lateral region ; mesial fold obscure or obsolete in the posterior half of the valve, becoming a little more con- spicuous anteriorly, but rarely or never strongly diiferentiated from the general surface of the valve; the beak incurved beneath that of the opposite valve; plications obscure as in the opposite valve, the stronger ones are confined to the mesial fold where they alternate with those of the sinus of the opposite valve, upon each lateral slope two or three exceedingly faint plications may occasionally be detected, but they are more apt to be entirely obsolete. Internally there is no cardinal process ; the hinge-plate is divided but not to the base at the apex of the valve, it is supported posteriorly by a median septum which is simple at first hut is divided above anteriorly, each division supporting one side of the hinge-plate, the support of the hinge-plate by the divided septum does not continue beyond the median incision of the hinge-plate itself so that no open crural cavity occurs, but rather an enclosed cavity roofed 226 MISSISSIPPIAN BRACHIOPODA over by the joined portion of the hinge-plate and open only in an anterior direction, the support of the hinge-plate by the septum is discontinued before the line of articulation is reached and from this point forward each lateral division of the hinge-plate is unsiipported, anteriorly each division is produced into the cavity of the valve as one of the crura. Surface of both valves marked by fine, rather regular concentric striae and by occasional strong lines of growth. i?fwiarfcs. — Shumard illustrated two different individuals with his original description of Khynchonella missoiiriensis, fig. 5a being a smaller and mvich smoother shell than figures 5b-e. The original description was evidently made from the larger and more strongly plicated shell, and that is here taken as the typical form of the species. Both of the illus- trated forms are commonly represented in collections of the Chouteau limestone fauna from central Missouri, and while an imperfect gradation from one form to the other can be traced, the two forms are easily distinct enough to be considered as different species. In his lists of species Shumard records R. obscura-pUcata, a name by which he undoubtedly designated the shell here described, although he never defined it. and the name by which Missouri collectors have known it since that time. In 1860 Hall described Rhynchonella obsolens, -without illustrations, from the goniatite-bearing Rockford limestone of Indiana, and his description agrees fairly well with examples of this smooth form from the Chouteau limestone of Missouri. In 1866 Meek and Worthen described and illus- trated as R. niissonriensis a shell from the same Rockford limestone which agrees satisfactorily with the smooth form of that shell as illustrated by Shumard, and it is more than probable that the observers had rep- resentatives of the same shell as that described by Hall. Under these circumstances, therefore, if we restrict the use of the name missouriensis to the larger shell of Shumard, either Hall's name or Shumard 's obsntra- ■plicata may be available for the form here described, and the latter of these must be ruled out because it was never properly defined. In their generic characters, as shown by serial sectioning of the shells, R. misscniriensis and R. obsolens are identical, but they cannot be included in any of the recognized generic divisions of rhychonelloid shells and have been made to constitute the new^ genus Shumardella. S. obsolens may be distinguished from 8. mi-ssoiiriensis by its smaller size, its mOre globose and less angular form, its much smoother and less strongly plicated shell, and by the more distinctly emarginate anterior outline. The species has some external resemblance to members of the genus Liorhynchus and has sometimes been incorrectly identified as L. boonen- sis, a rare species which was originally described from the Burlington limestone. HoW20H.— Chouteau limestone. RHYNCHOPORA 227 Genus RHYNCHOPORA King Description.— Shell rhyncholliform, below medium size, usually pentan- gularly ovate in outline, the mesial fold and sinus well developed in the anterior half of the shell, both valves marked by simple, subangular or rounded plications which are sometimes longitudinally grooved towards the front. Internally the dental lamella^ are well developed in the pedicle valve. Brachial valve with a strong median septum in the rostral por- tion, which is divided internally to form the walls of a crural cavity ; this is covered over on its cardinal side by the undivided hinge-plate, the hinge-plate continuing anteriorly beyond the anterior termination of the crural cavity; the crura formed by the anterior extension of that part of the hinge-plate opposite the lateral walls of the crural cavity. Shell structure punctate. Remarks.— "No opportunity has been afforded the writer to make a study of the internal characters of R. geinitziana, the genotype of Rhyn- chopora, so there is a po.ssibility of a wrong interpretation of the genus in this place. Up to the present time the one essential genei'ic character which has been recognized is the punctate structure of the shell, but in R, piistulosa, the only American species recognized by Hall and Clarke^ and by Schuchert;- the undivided hinge-plate and the complete closure of the crural cavity except anteriorly, are good differential characters. All other species included in the genus in this place, except one, agree in the character of the hinge-plate and crural cavity with R. pu-itulosa. The puncate structure of the shell is conspicuously developed in only one of the species here recorded, R. beecheri, which has been observed only in the condition of internal casts and impressions of the exterior, no serial sections of the rostral portion of the shell have been made, but the hinge-plate and crural cavity are apparently as in R. piistulosa. The Pennsylvanian species R. illinoisensis is another one which is conspicuously punctate, but its internal characters have not been worked out. In R. piistulosa the punctate structure of the shell is so obscure as to almost lead one to believe, at times, that it is absent, and in one or two of the species here included in the genus no punctate structure has yet been observed. Another character which differentiates most of these shells from other Mississippian rhynchonelloids is the longitudinal grooving of the flattened plications towards the front, especially those of the fold and sinus, this condition being altogether similar to that in Wilsonia and some other older rhynchonelloids. This character is not shown upon any of the illustrations of R. geinitziana which have been available for examination, and it is not present in R. hamburgcnsis described in this work. On the whole, R. hamburgensis seems to corre.spond most closely 1 Pal. N. Y., vol. 8, pt. 2, p. 210. (1894.) 2 Synop. Am. Foss. Brach., p. 366. (1897.) 228 MISSISSIPPIAN BRACHIOPODA in the sum of all its characters, with the genotype, although the punctate structure is much more obscure. It is possible that future investigations of this group of shells will make it necessary to recognize one or more additional genera. Bhynchopora hamburgensis "Weller Plate XXIX, Figs. 19-30 1910. Hhyncliopora Jiamburgonsis Weller. Bull. Geol. Soe. Am., vol. 21, p. 515, fig. 17. . Description. — iiheW small with valves very unequally convex in mature specimens, triangularly subovate in outline, the postero-lateral margins meeting at the beak in an obtuse angle, the antero-lateral margins rounded, the anterior margin nearly straight or a little concave. The dimensions of two examples are: length 10.2 mm. and 9 mm., width 11.1 mm. and 9.8 mm., thickness 8 mm. and 5.5 mm., width of sinus in front 8 mm. and 6.3 mm. Pedicle valve shallow, convex in the umbonal region, the surface curv- ing rather abruptly to the postero-lateral margins, gently convex from the umbo to the antero-lateral margins, and strongly arched in adult shells along the median line from the beak to the front margin ; mesial sinus originating near the middle of the valve as a broad, shallow, concave depression which becomes deeper anteriorly, not abruptly depressed below the lateral slopes of the valve, produced anteriorly in adult shells in a broad lingual extension rounded in front, whose surface lies in nearly a right angle to the plane of the valve; beak rather broad, not strongly incurved, pierced by a subcircular foramen, rather conspicuously ex- tended posteriorly beyond the opposite valve ; delthyrium broadly triangu- lar, partially filled by the beak of the opposite valve, communicating at J K Fig. 20. — A series of eleven cross-sections of tlie rostral portion of the shell of Rhynchopora hamburgensis (X 2%); A to E, the pedicle valve, showing the dental lamellae; F to K, the brachial valve, showing the undivided hinge-plate, the median septum, and covered crural cavity. the apex with the foramen which encroaches upon the beak, deltidial plates not observed ; plications simple, rounded or subangular, originating at the beak, from three to six, more usually four or five, occupy the sinus, and about five each lateral slope. Internally the hinge teeth are sup- ported by a pair of short dental plates which quickly become obsolete in front of the articulation of the hinge. RHYNCHOPORA 229 Brachial valve more convex than the pedicle, becoming gibbous in mature shells, the umbonal region flattened longitudinally or sometimes with a slight mesial depression, the greatest convexity at or near the front margin, the surface sloping from the point of greatest convexity to the beak with an increasing curvature and with a more or less abrupt curva- ture to the front, laterally from the median line the surface is at first gently convex but soon curves abruptly to the margins; the mesial fold obsolete in the posterior half of the valve and only moderately or not at all differentiated anteriorly ; the beak broad, incurved beneath that of the opposite valve; the plications similar in form and number to those of the opposite valve and alternate with them. Internally the cardinal process is lacking and the hinge-plate is undivided, although the median portion is differentiated from the lateral portions, it being thinner and usually either a little concave or a little convex; a median septum is present at the beak which is soon divided, one branch supporting each of the lateral divisions of the hinge-plate, but because of the continuous hinge- plate the pit between the divisions of the septum is not an open crural cavity as in Camarotcechia, but is a covered excavation open only towards the front; a little posterior to the articulation of the hinge, the median septum and its divisions which support the hinge-plate become discontinuous, the septum continuing as a gradually disappearing ridge for about one-fourth the length of the valve from the posterior extremity. Surface of both valves, apart from the plications, nearly or quite smooth, except for a few obscure lines of growth near the anterior margin of adult shells. The shell structure is minutely punctate and in at least one specimen the perforations are arranged in longitudinal rows, a single row upon each slope of each plication. /?e»?(.ar^s.— This species occurs abundantly in the Hamburg oolite of Kinderhook age, at Hamburg, Calhoun County, Illinois. Externally, it somewhat resembles, in size and general form, the Camarotcechia clicniteauensis from the Chouteau limestone, but its plications are less angular, its fold and sinus are less abruptly differentiated from the lateral slopes, and its beak is less incurved and more produced posteriorly. Internally the two forms are fundamentally different, Z?. hamhiirgensis having the continuous hinge-plate of the genus Rhynchopora, while in C. chouteauensis the hinge-plate is medially divided and the characters are those of Camarotcechia. The two species are also differentiated by the punctate shell structure of H. Jvaniburgensis. The intefnal characters of the species have been determined by the study of serial sections made by grinding detached valves. These de- tached valves have, of course, been subjected to accident dui'ing depo- sition, and in no case have the crura been detected, although they were undoubtedly present as anterior prolongations from the lateral divisions of the hinge-plate. In some of the specimens examined the median por- 230 MISSISSIPPIAN BKACHIOPODA tion of the hinge-plate has also been destroyed, this part being distinctly thinner and more delicate than the lateral portions and therefore much more easily destroyed. The continuous hinge-plate has been observed in a sufficient number of individuals, however, to make it certain that that was the normal condition of the species. The punctate structure of the shell is an obscure feature and in many individuals it cannot be detected at all on account of the condition of preservation of the shell. It is occasionally shown, however, and in the specimen in which it is best exhibited the perforations are not distributed uniformly over the entire shell but occur in longitudinal lines, one upon each lateral slope of each plication. This is probably the normal condition towards the beak but it is possible that they become more scattered towards the anterior margin of the shell. Horizon. — Hamburg oolite of the Kinderhook. Rhynchopora pustulosa (White) Plate XXIX, Pigs. 14-18 ; Plate XXIV, Pig. 82 1860. Kliynchonella pustulosa, White, Jour. Boston Soc. Nat. Hist., vol. 7, p. 236. 1894. lihynchopora pustulosa Hall and Clarke, Int. to Study of Braeh., pt. 2, pi. 44, figs. 26-29. 1895. Rhynchopora p^istulosa Hall and Clarke, Pal. N. Y., vol. 8. pt. 2, pi. 58, figs. 1-4. 1901. Bhynchopcra pustulosa Weller, Trans. St. Louis Acad. Sci., vol. 11, p. 157, pi. 13, figs. 4-6. 1904. Rhynchopora pustulosa Greger, Am. Geol., vol. 33, p. 298-299, figs. 10-12. 1910. Rliyuchopora pustulosa Weller, Bull. Geol. Soc. Am., vol. 21, p 514, fig. 16. Description.— 'SheW below medium size, subpyramidal in form, wider than long, the greatest width near or in front of the mid-length of the shell, the postero-lateral margins a little concave, meeting at the beak in an obtuse angle, the lateral margins rounded, the anterior margin nearly straight or gently convex. The dimensions of a nearly perfect specimen are: length 12.3 mm., width 12.6 mm., thickness 10.3 mm., width of the sinus in front 8.5 mm. Pedicle valve convex in the umbonal region with a sigmoidally curved slope to the cardinal margin, to the antero-lateral margin the surface is gently convex and from the beak to the front margin along the median line it is strongly arched in nearly a semicircle ; the mesial sinus is obsolete in the posterior half of the valve, it originates near or in front of the middle of the valve as a broad, shallow, flattened depression and continues as such to the anterior margin, anteriorly it is produced in a broad, lingual extension rounded in front with a serrate margin, whose surface in front lies in nearly a right angle to the plane of the valve ; the beak large, moderately incurved, perforated by a large, subcircular foramen; RHYNCHOPORA 231 the delthyrium broadly triangular, nearly filled by the beak of the opposite valve, communicating at its apex with the foramen which en- croaches upon the beak of the valve; plications rather coarse, rounded or subangular, simple, originating at the beak, three or rarely four oO ^