v : 8»»ifSKji»SSS i^^^viyj '"^~ ^ - " ^ -/~^0 £&$-$ ., iiWA. ;Vv^ ( v w • w v v> v~^ -^v^ > > > > ? • > . > ;> > ~» > >»> »>» >3f>> :>3HK> >!2BK> L1BRAR UNIVERSITY CALIFORNIA EARTH SCIENCE LIBRARY No. > "\S*^> ~> > > r»^j t> > > - > > » .H3|> 7> >~>^ .^>^?> > ^ >3 ^feO^» ^> ^ >^ :s»:x3L* '• ' > > > > ^ >Ts»^> ^)»^3> »»^1> T> > •> '3>- . ^>~)» » ^»^> »»i>- y>»:j> *-> >» » > >j>»> > )>•> >- "»» ' » >:* > >v . o >•> ^» > > . <-=-, > > » > y » ^s> > >' ft ^^e> > go D^l> > > 3»> 0>> ! " ^>> - ^>^ > }> 2 -» 3) > > >v) >^> D^>" , T, X5S ^a»i.^»>: )3>^ )^S> 1> ^m^ . > > > > » > 3»:?» t>-T» T} > :> ^ • >>J>Z3i " ,. •, > % > > . > o ^ > -e/O ' > ) > > > , >» > > > > » > 3! "J> ^ I » ::> ; ; * >, • -> •> > : > » ' . > > »> GEOLOGICAL SURVEY STATE OF IOWA: EMBRACING THE RESULTS OF INVESTIGATIONS MADE DURING PORTIONS OF THE YEARS 1855, 56 & 57. JAMES HALL, State Geologist; J. D. WHITNEY, Chemist and Mineralogist. VOLUME I. PART II : PALEONTOLOGY. PUBLISHED BY AUTHORITY OF THE LEGISLATURE OF IOWA. 1858. PRINTED BY CHABLES VAN BENTHUYSEN. CHAPTER VIII. GENERAL REMARKS — FOSSILS OF THE HAMILTON GROUP — FOSSILS OF THE CHEMUNG GROUP — FOSSILS OF THE BURLINGTON LIMESTONE — FOSSILS OF THE KfiOKUK LIME- STONE FOSSILS OF THE Si. LOUIS LIMESTONE FOSSILS OF THE K.ASKASKIA LIME- STONE — FOSSILS OF THE COAL MEASURES. I HAD proposed, in this part of the Report, to illustrate by descriptions and figures some of the most characteristic fos- sils of each of the several groups and formations which constitute the geological series occurring in Iowa. Since, however, it was necessary to limit the work within a mo- derate compass, the entire series could not be satisfactorily exhibited, and I have chosen therefore to devote the means at my disposal to a more full illustration of certain portions which I considered more important in the present state of our knowledge. The sequence of the Lower Silurian and Upper Silurian formations have, for the most part, been described and illustrated in the Reports of Dr. D. D. OWEN; while the higher groups, especially the Carboniferous limestones, have received less attention. Moreover, as I have already shown in a published paper, and more in detail in Chapter III of this volume, the Carboniferous limestone formation of the Mississippi valley will admit of several subdivisions ( some of which have not before been recognized), each one being readily determined by its fossil remains, and which seem to me to be as restricted in their geological range as are those [ IOWA SURVEY.] 60 474 GEOLOGICAL SURVEY OF IOWA. of any established groups of the Silurian and Devonian periods. An examination of the fossils from the geological horizon of the Hamilton and Chemung groups of New- York ( and which is in fact a continuation of the same beds) shows, that while there are many species identical with those of the same group in its eastern localities, there are a still larger number of new species ; and which, since the physi- cal conditions of the mass were not essentially different, can only be attributed to the influence of geographical distance. Having partially the means of illustrating in the fossils the changes which have taken place in the fauna of these epochs, I have given, to some extent, both the already known and the new species. The Hamilton and Chemung groups, after being traced almost continuously from the western slopes of the Appala- chians, is recognized in the Mississippi valley, both by lithological features and by fossil remains ; and we take up again in Iowa our investigations of the fossils of these groups, after an interval of nearly fifteen degrees of longitude. Among the Carboniferous limestones, the Burlington lime- stone has given ample materials for the illustration of its ancient fauna. The Keokuk limestone has also proved pro- lific of characteristic fossils ; while the St. Louis limestone has afforded, comparatively, so few species that I have been constrained to go beyond the limits of the State for many of the characteristic examples of its fossils. The Kaskaskia limestone, so well developed at Kaskaskia and thence along the river bottom to Chester and as far as Fountain bluff, is unknown up to the present time within the limits of the State of Iowa. I have, nevertheless, felt it my duty to illus- trate in some measure its fossil remains, in order to prove its distinctness from the Keokuk limestone, with which it has heretofore been erroneously identified as the "Archi- medes limestone". The fossils selected for this purpose are PALAEONTOLOGY OF IOWA. 475 of the same class, and represent the forms, chiefly, of Cri- noidese and Brachiopoda, which are most commonly found in these limestones. No species common to the two lime- stones have been observed by myself; and though probably such do occur, they are certainly not numerous, nor among the prominent forms which every where mark the two rocks. Besides the collections which I have been able to procure, I have availed myself in many instances of those already made. Mr. A. H. WORTHEN very kindly offered me the use of his extensive and magnificent collection of Crinoidese, as well as of -other fossils ; and but for this liberality, the work would have been far less fully illustrated. Such collections can only be accumulated by the devoted attention of many years ; and in expressing my own indebtedness to Mr. WOR- THEN, I may express the obligations under which geology rests for this contribution, and which will be gladly acknow- ledged by every student and votary of the science. The collections made by Mr. WHITNEY and Mr. HUNGERFORD from the Hamilton group on Lime creek near Rockford, pos- sess peculiar interest ; inasmuch as they present us with forms more nearly allied to those of Central Europe, than the species wThich occur in more eastern localities of the same formation. The collections made by these gentlemen, and by Mr. WORTHEN at Independence and other centrally situated localities, show that in progressing in a northwes- terly direction, changes are observed which can only be attributed to climatic or geographical influences. The explorations both in the Hamilton and Chemung groups, as well as in the Carboniferous limestones, are yet very incomplete towards the northern part of the State, and we have reason to believe that discoveries of much interest will be made in these formations in that direction. The surveys of the Desmoines valley in 1856 proved the Gypsum formation to lie above the productive Coal measures . 476 GEOLOGICAL SURVEY OF IOWA. and I had hoped, before the conclusion of this Report, to be able to present some fossil remains from this group. The examinations yet to be made will be more especially directed to the region occupied by the Coal measures and the Gypsum formation, and we may hope to present some more exten- ded information regarding these formations in a succeeding Report. FOSSILS OF THE HAMILTON GROUP. CORALS. ACERVULARIA ( SCHWEIGGER ). " CORAL compound, fasciculate, or more often massive, in- creasing by calicular budding ; cells presenting two separated walls as in Aulophyllum ; rays well developed between the walls, but much less in the central area ; no columella ; transverse septa little developed". — EDWARDS and HAIME, Mon. Polyp. Fos. p. 414. Acervularia davidsoni ? PLATE I. FIG. 8 a, b. Acervularia davidsoni : EDWARDS and HAIME, Monograph des Polypiers fossils, etc. pa. 418, pi. 9, f. 4, 4 a & 4 b. CORAL astrgeiform ; surface plane or subhemispherical ; cells irregularly polygonal, unequal, the walls slightly zig- zag ; interior wall scarcely defined, and often marked only by the abrupt downward bending of the rays, which form within this area a deep cup ; rays 32 to 40 in the outer di- vision of the full-grown cells, often 20 in the younger cells, distinctly denticulate towards the sides, less distinctly to- wards the centre, in which there is sometimes a papilliform PALEONTOLOGY OF IOWA. 477 elevation which rises as high as the outer walls. In the un- worn cells the inner wall rarely presents any interruption to the rays, some of them dying out or becoming less distinctly denticulate within this area. The specimen figured is much weathered, and its outer area exhibits a gently in- clining surface and a deep depression within the inner wall, with a scarcely elevated point in the centre. Other specimens, with the cup entire, are less depressed; and some specimens, which do not appear to have been worn before imbedding, are scarcely depressed within the inner walls. Although these differ in some slight degree from the figures and descriptions cited above, I am inclined to regard them as identical, more particularly since specimens from different localities in Iowa show a considerable variation in external appearance as well as in the prevailing number of rays. The cells range in their greatest dia- meter from one-quarter to one-half an inch, presenting upon the surface of large specimens every degree of development. Fig. 8 a. A weathered fragment of this species. Fig. 8 b. An enlargement of one of the cells. Geological formation and locality. In limestone of the age of the Ha- milton group of New- York : Near Davenport, Rockingham, New-Buffalo, Pine creek, Iowa city and other places in Iowa ; Hamburgh, etc. in Illinois. Aceinilaria profunda (n. s.). PLATE I. FIG. 7 a, b, c. CORAL astrseiform, subhemispheric ; cells irregularly poly- gonal, unequal in size, often somewhat circular in the young and half grown conditions ; walls thin, scarcely undulating ; inner wall undefined ; cup abruptly and deeply depressed from a little within the outer wall ; centre marked by a pa- pilliform node : rays thin, slender, from 36 to 46 in each cell (41 to 46 in full grown individuals), denticulate on the sides from the margin to the base of the cup ; some of the rays disappearing between the margin and the centre. This species, in general aspect and in details of structure, is very distinct from A. davidsoni. The cells are less compactly arranged, and the outline is often some- what circular, particularly in the young state. The cells are very unequal in dimen- sions, even in the same specimen, and this difference in the size is not always accompanied by a corresponding difference in the number of rays. The walls of this species are less strong than those of the preceding species, and scarcely undulating; while the rays are much more slender, and the denticulations more regular. 478 GEOLOGICAL SURVEY OF IOWA. Fig. 7 a. Part of a large hemispheric mass, showing several young cells, some 'nearly circular : natural size. Fig. 7 b. Transverse section of a cell, enlarged, from a polished surface. The inner wall is not defined, and many of the rays are continuous to the centre of the cup. Fig. 7 c. A- portion of a cell, enlarged, showing the denticulated rays. Geological formation and locality. In limestone of the age of the Ha- milton group of New- York : Independence, Iowa. CLADOPORA (HALL). " CORAL ramose or reticulate ; branches cylindrical or slightly compressed, terminations terete : coral composed of a series of tubes or cells radiating equally on all sides from the axis, and opening upon the surface in rounded or suban- gular expanded mouths ; cells more or less closely arranged, but not always contiguous, and apparently destitute of septa or rays".— Pal. N.Y. Vol. ii, p. 137. • Cladopora dichotoma ( n. s.). PLATE I. FIG. 5. CORAL ramose ; branches round, dichotomizing, ascending; cell apertures in unworn specimens somewhat expanded and broader below, in worn specimens round ; cells arranged in alternating or somewhat quincunx order, distance from each other greater than the diameter of the cell, sometimes more closely arranged : surface smooth or granulate. This species bears a distant resemblance to some of the Niagara species of this genus; but is much more robust, with the cells much larger and more distantly arranged. Geological formation and locality. In calcareous rocks of the age of the Hamilton group : New-Buffalo, Iowa ; Hamburg, Illinois. GENUS STRIATOPORA (HALL). " CORAL ramose, corolla solid ; stems composed of angular cells ; apertures of cells opening upon the surface in expan- ded angular cup-like depressions ; interior of the cell rayed or striated ; striae extending beyond the aperture of the cell". — Pal. N.Y. Vol. ii, p. 156. " PALAEONTOLOGY OF IOWA. 479 Striatopora rugosa ( n. s.). PLATE I. FIG. 6. COKAL ramose, frequently bifurcating ; branches very gra- dually tapering ; cells somewhat distant, arranged in alter- nating series, subcylindrical below and gradually expanding towards the aperture, with the walls much elevated on the basal and lateral margins. This species is much more robust than the S.flexuosa of the Niagara group, with stronger and more rigid branches : the cell apertures are smaller, less angular, and more distantly arranged. The specimens examined are all more or less worn, and the surface characters not well preserved. Some of the cells show the interior striation which characterizes the genus. There is a similar species in the shales of the Hamilton group in New-York. Fig. 6. A fragment of this fossil : natural size. Geological formation and,. locality. In shaly limestones of the age of the Hamilton group of New- York : New-Buffalo, Iowa. 6RDJOIDU! OF THE HAMILTON GROUP. GENUS ACTmOCRIMJS (MILLER). [ SUBGENUS ] MEGISTOCRINUS (OwEN & SHUMABD). BODY depressed, subspheroidal or broadly urnshaped : basal plates three, usually anchylosed, and scarcely extend- ing beyond the edge of the column ; second series of plates (often appearing as the basal series) six, five radials and one anal : radial plates three in five series, interradial plates six to ten or more in five series ; anal plates seven to thirty or more ; each upper radial supporting two and some- times three supraradial plates : from each upper sloping side, supraradials, often in double series above the first plate ; brachial plates numerous ; arms composed of numerous thin joints arranged in double series ; subaxillary plates none to six or nine. 480 GEOLOGICAL SURVEY OF IOWA. The successive ranges of plates in the species known, present the number of three in the first, six in the second, twelve in the third, etc. The spedes of this type have so much the structure of ACTINOCRINUS, that a little extension of the generic characters of that genus would include them. Our spe- cimens, however, approach more nearly the Genus PRADOCRINUS of DE VERNEUIL, to which they are closely allied in structure; but having a scarcely visible calyx, they do not correspond with the description and figures given. The Genus MEGISTOCRINUS, proposed by OWEN and SHUMARD in 1852, has essen tially the structure of the species under consideration, in the basal, second and third series of plates, as well as in the relations of the parts of the calyx. A farther comparison of specimens, however, shows that these forms are but modifications of the typical generic form of ACTINOCRINUS, and do not appear to me to be separable upon fundamental structure. The illustrations under the Genus ACTINOCRINUS of the Burlington limestone, in this volume, will show more clearly the relations here indicated. Actinocrinus (Subgenus Megistocrinus ) latus (n.s.). PLATE I. FIG. 1 a, b. BODY depressed spheroidal or broadly urnshaped : base broad, nearly flat or slightly concave towards the column ; base composed of three closely joined or anchylosed plates, presenting a flat hexagonal disk which barely extends beyond the column. First radial plates hexagonal, wider than high, base and upper margins straight and parallel, the base a little the longer ; second and third radials hexagonal (one penta- gonal), base straight. Each third radial supports on its upper sloping sides two superradials, which, in the anterior and antero-lateral rays, are each succeeded by a second super- radial in the same series, and in the postero-lateral rays each first superradial supports a pair of diverging second super- radials, and each of these, two others in the same direction, giving four ranges of superradials in those rays : these are succeeded by the brachial and arm-plates, giving, apparently, but four arms to the postero-lateral rays, while each of the other rays has the same number. First interradials hexagonal, as large as the second radials, succeeded by two others, each PALAEONTOLOGY OF IOWA. 481 of which is as large or larger than the third radial plate ; a third, fourth, fifth and sixth series of smaller interradial plates. First anal plate as large as the first radial plates, supporting one central large plate, and on the outer sloping edges of each side a series of two plates of the same dimen- sions as the second and third radials, while above and within these are several series of smaller plates to the number of more than thirty. Dome broad, depressed hemispheric, composed of a great number of small plates with a subcentral proboscis or spine. FIG. 53. — Diagram of the plates composing the body, below the arms, of Megistocrinus latus. This species resembles one in the Hamilton group of New- York, but is larger and the basal plates more extended beyond the column : the form and proportion of the plates also differ in some degree. The surface of each plate is distinctly depressed in the New- York species, and the margins at their junction form an elevated ridge ; while the plates of the Iowa species are individually convex. Fig. 1 a. The summit of the specimen. Fig. 1 6. Basal view of the same. Geological formation and locality. In the calcareous shales of the age of the Hamilton group of New- York : New-Buffalo, Iowa. f IOWA SURVEY.] 61 482 GEOLOGICAL SURVEY OF IOWA. S TAXOCRIMIS (PHILLIPS). BASAL plates five, small ; radial plates three in five series ; arms subdividing upon the third radial, and frequently dichotomizing above this point ; arms and branches com- posed of a single series of joints. Interbrachial and axillary plates. The definitions and illustrations of this genus, which have fallen under my obser- vation, are not as clear as could be desired; and it is evident that the genus, as recognized in Great Britain, contains a heterogeneous assemblage of species. PICTET has selected the Cyathocrinus tuberculatus of MILLER as the type of this genus; and following the characters there presented, I believe the following species may be placed under the same designation, though presenting some slight differences. GOLDFUSS, in his fig. A, pi. ~,8*, represents a double interradial plate truncating the upper angle of one of the basal plates; but in the enlarged figure, this plate is re- presented as lying between the second radials and resting on the sloping edges of two adjacent first radials. The figure of PICTET is like the first named figure of GOLD- FUSS, while the figure in MUBCHISON'S Silurian System represents the interradial plate as in the fig. B of GOLDFUSS. Taxocrimis interscapularis (n.s.). PLATE I. FIG. 3. BODY narrow, turbinate below the first bifurcation of the arms : basal plates five, short, with the angular summit much pointed upwards between the lower radial plates ; ra- dial plates three in each series, much wider than high, the two lower series quadrangular ; upper radial broad pentago- nal, with the two upper sloping sides supporting a double series of arm-plates ; interbrachial plate narrow, resting the base slightly on the second radial plates, with its upper ex- tremity lying between the second arm-plates. Arms ten ; those on the exposed side bifurcating on the fifth plate above the base, and the adjacent parts again bi- furcating upon the eighth and tenth plates respectively, while the outer divisions of the same arms continue simple * Petrefacta Gftrmanise, plat* Iviii. PALAEONTOLOGY OF IOWA. 483 to the fifteenth or seventeenth plate. The arms (outer side of the figure), have their first bifurcation on the eighth plate from the base. A small axillary plate is intercalated between the arms at the first, and sometimes in the second bifurcation. This neat and symmetrical species differs sufficiently from the known Cyathocrinus in the character of its base, and resembles none of the previously described Ameri- can crinoids, so far as I know. Fig. 3. View of a specimen imbedded in argillaceous limestone. Geological formation and locality. In shaly limestone of the age of the Hamilton group : New-Buffalo, Iowa. GEKUS For generic description, see SYNBATHOCR.INUS under the head of Crinoidese of the Burlington limestone. Synbatliocrinus matutinus (n.s.). PLATE I. FIG. 2, BASAL plates undivided, forming a slightly projecting disc in the specimen : first radial plates wider than long ; second radials longer than wide, obtusely angular along the centre ; brachial plates quadrangular, and subangular longitudinally along the centre : column round, composed near the base of alternating larger and smaller rings. The only specimen seen is a fragment, imperfect at the upper extremity, with the surface much broken-, and particularly the basal and first radial plates, while the surface of the arm-plates has been exfoliated. The structure, therefore, is not very satisfactorily determined, though the peculiar form of the crinoid and the succession and arrangement of the plates are sufficient to distinguish it from any other established genus of crinoids. Fig. 2. View of an imperfect specimen imbedded in shaly limestone. Geological formation and locality. In shaly limestone of the age of the Hamilton group, associated with Strophodonta demissa : New-Buffalo, Iowa. 484 GEOLOGICAL SURVEY OF IOWA. GENUS PENTREHITES (SAY). FIG. 54.— GENERIC FORMULA. Basal plates 3, of which one is smaller than the others. Radial plates 1X9, forked, large. Interradial plates 1X5, lanceolate, small. Pseudo-ambulacral areas 1X5, covered by pinnules. Mouth 1, central. Anal aperture 1, lateral. Ovarian apertures 2X5, arranged around the mouth. "BODY variable, globose, ovoid, pyriforni, or clavate : basal plates three, one smaller and quadrangular, the other two equal in size and pentagonal ; radial plates five, equal in form and size, two resting each on one of the sides of the two pentagonal plates, while the three others are alternate and in contact each with two of the basal plates. The little quadrangular basal plate does not correspond, as might be supposed, with the anal side, but with a regular side, as in PLATYCRINUS. These radial plates are divided in the middle by a sinus more or less wide and deep, giving them the form of a two-pronged fork : this sinus contains the pseudo- ambulacral areas. The forks of the radial plates alternate with five little interradial pieces, which are lanceolate, subtetragonal, more or less elongate, and meeting at the superior central opening. " The pseudo-ambulacral areas are composed of three series of plates superimposed upon each other. The middle is filled with a series of compressed tubes disposed parallel to the sides of the forks of the radial plates, and succeeded by a single median lanceolate or linear plate, ornamented on each side by a great number of little transverse poral plates, al- ternating with transverse groups of still smaller plates (sup- plementary poral pieces). Filiform and articulate appendages, like the pinnules of the arms of other crinoids, and corre- PALEONTOLOGY OF IOWA. 485 spending in number and in their bilateral arrangement with those of the lateral pores, complete the series of poral pieces. " A central pentagonal opening is seen on the summit : this corresponds to the mouth of the animal. It is surrounded by four other smaller openings in the summit of the interradial pieces, and divided in the middle by a longitudinal lamella : the opening in the fifth radial piece, a little larger than the four others, has two lamellae, which form three canals, of which the middle one corresponds to the anus, and the two lateral ones, as those of the other radial pieces, to oviducts of the animal. " The stem is formed of little cylindrical articulations, having a very small circu- lar opening : it appears to have been very short." Peiitremites subtrancatus (n.s.). PLATE II. FIG. 3. TURBINATE or reversed pyramidal, the base round, gradu- ally becoming angular above, distinctly pentangular at the base of the pseudambulacral spaces ; base small, almost pointed, apex broad subtruncate above ; basal plates small, less than half the length of the body ; radial plates less than once and a half as long as the basal plates, slightly divided above for the reception of the pseudambulacral plates ; in- terradial plates small, rising above the centre when complete ; summit convex, flattened in the centre ; pseudambulacral spaces short, abruptly convex in the middle ; poral plates fifteen or more in each series ; ovarian apertures small, round. This species belongs to the same type of form as P. reinwardti, from which the one here described differs in having relatively a much shorter base, is more rapidly expanding above, the summit less elongated and much more obtuse, there being little contraction from the pseudambulacral spaces to the summit of the interradial plates. The pseudambulacral spaces in P. reinwardti are much narrower and the sides more nearly parallel; the poral plates present a flattened or depressed line, while in this one they form an abrupt convex area. A similar species P. striatus, from the Corniferous limestone, has the plates deeply striated parallel to their margins, and the pseudambulacral areas broader and less abruptly convex, and the interradial plates less extended. Geological formation and locality. In the calcareous shale of the age of the Hamilton group of New-York : New-Buffalo, Iowa. 486 GEOLOGICAL SURVEY OF IOWA. BRACHIOPODA OF THE HAMILTON GROUP*. Oitliis suborbicularis (n.s.). PLATE II. FIG. 1 a - e. SHELL depressed orbicular ; valves almost equally convex, length and breadth about as four to five ; hinge line very short. Dorsal valve regularly convex, a little flattened at the cardino-lateral margins ; beak elevated and slightly incurved beyond the plane of the area. Ventral valve slightly the more convex, most convex near the umbo ; beak slightly more elevated than the opposite, scarcely incurved : area about one third as high as wide : foramen large ; width and height about equal. SURFACE finely striated ; striae increasing by implantation, gradually curving outward towards the margin, and bending upward to the hinge line, crossed by fine concentric striae, and sometimes by imbricating lines of growth. Interior marked near the margin by strong striae which are faintly visible half way to the beak ; the entire surface finely punctate. Ventral valve with strong cardinal teeth, and muscular impressions limited by the dental lamellae. Dorsal valve with strong brachial processes and a small car- dinal process. This species bears some resemblance externally to O. vanuxemi of the Hamilton group, as it occurs in its more circular forms in New- York; but is proportionally broader, and the valves more equally convex. In its muscular and vascular impres- sions it is conspicuously distinct, as well as in the cardinal process and strongly marked ridge down the centre of the dorsal valve. It bears, also, much resemblance to a species of the Lower Helderberg limestone, but careful comparisons show it to be distinct. The specimen figured is somewhat compressed towards the margins, so that a profile view does not present the true form of the shell. Fig. 1 a, b. Dorsal and ventral views of an entire individual. Fig. 1 c. Cardinal view of the same enlarged. Fig 1 d. Interior of a dorsal valve, showing the brachial and cardinal processes. Fig. 1 e. Interior of a ventral valve of a small individual, showing the cardinal teeth. * For generic descriptions of the Brachiopoda, see pages following the specific de- scriptions at the end of the volume. PALAEONTOLOGY OF IOWA. 487 Geological formation and locality. In calcareous shales of the age of the Hamilton group : Rock-island (Illinois), opposite Davenport (Iowa). Oithis vanuxemi. PLATE II. Fio. 2 a - i, 3 a -/. Orthis vanuxemi : HALL, Report of the Regents of the University on the N.Y. State Col- lections of Natural History for 1856, p. 95. SHELL depressed orbicular, varying from circular to trans- versely broad oval, and rarely a little longer than wide, resupinate. Ventral valve most convex near the beak, gra- dually depressed below and flattened towards the front ; beak elevated, scarcely incurved. Dorsal valve most convex a little above the centre, an undefined depression down the middle, which expands into a broad flattened space, some- times giving the base a straight appearance ; beak scarcely denned : length of area about one-third the width of the shell : foramen broad, partially filled with the strong car- dinal process. SURFACE marked by fine closely arranged radiating tubular stride, which increase by bifurcation and implantation, and are crossed by very fine concentric lines, and towards the margins by imbricating lines of growth ; striae with frequent tubular openings upon the surface. Interior surface finely punctate. Interior of ventral valve marked by a large foliate or flabelliform vascular impression, and in older shells a strongly defined impression of the ad- ductor muscles a little above the centre of this, and a pro- minent cardinal process which is continued below in a ridge along the centre of the valve. Margins crenulate with the radiating strise, which are sometimes visible more than half way to the beak of the shell. The specimens of this species from Rock-island are usually longer than wide : in other localities, they are more nearly circular; and notwithstanding the variation from the prevailing form of the New- York specimens, there appears to be no specific difference. 488 GEOLOGICAL SURVEY OF IOWA. Tig. 2 a, b, c. Ventral, dorsal and profile views of a specimen of the usual form of the species in its more northwestern localities. Fig. 2 d. Cardinal view, enlarged, to show area and foramen. Fig. 2 e,f. Dorsal and ventral views of a specimen from the same geological position in Missouri. Fig. 2 g, h. Interior of ventral and dorsal valves. Fig. 2 i. Enlargement of striae. Fig. 3 a, b. Ventral and profile views of a specimen of medium size, from the shales of the Hamilton group in New-York. Fig. 3 c, d. Interior of ventral and dorsal valves from New-York specimens; the ventral valve showing some slight differences in form and divergence of the teeth from 2 g. Fig. 3 e. Interior of a large ventral valve from the Hamilton group of New-York, show- ing the vascular and muscular impressions : the teeth are broken. Fig. 3 f. Enlargement of the striae, showing the punctate surface and more distinct tu- bular openings. Geological formation and localities. In calcareous shales of the age of the Hamilton group : near Davenport and New-Buffalo, Iowa ; Rock-island, Illinois, and several localities in Missouri ; the Hamilton group in Central and Western New- York. Orthis iowensis. PLATE II. FIG. 4 a - i. SHELL resupinate, transversely oval or subglobose, with a deep sinus in front; hinge line less than two-thirds the greatest width of the shell. Ventral valve much the less convex, greatest convexity near the beak, and flattened to- wards the margins, with a deep sinus from the middle to the base of the valve ; beak elevated slightly above the opposite, pointed, not incurved. Dorsal valve extremely gibbous, greatest convexity about the centre of the valve, and slop- ing abruptly to the sides ; umbo arched ; beak prominent, slightly incurved over and projecting beyond the hinge line. Area small ; foramen narrow. SURFACE marked by fine closely arranged radiating tubular striae which increase by bifurcation and interstitial addition, and are crossed by fine concentric striae and a few imbricating lines of growth; radiating. striae presenting numerous tubu- lar openings upon the surface, and marked by fine pores or punctse over the entire surface. PALAEONTOLOGY OF IOWA. 489 Interior of ventral valve marked by strong muscular im- pressions, which are limited by the dental lamelles and divided in the centre by a strong ridge, presenting a qua- drangular area below the hinge line, the vascular impression proceeding in radiating impressed lines from the base of this quadrangular area : teeth strong, prominent. Dorsal valve deeply concave, with strong prominent brachial processes, and a median cardinal process which is sometimes bilobate. Entire interior of shell punctate : striae marking the inner margins of both valves, but rarely extending far beyond. This species is closely related to Orthis propinqua of the Upper Helderberg lime- stone, to O. tulliensis of the Tully limestone, and to O. multistriatus of the Upper Pentamerus limestone. It may, however, be distinguished from all these by its shor- ter area and more pointed, as well as more arched, beaks, as also by the form of the muscular impressions of the ventral valve and the cast of the same, as well as the direction and division of the vascular impressions below. Fig. 4 a, b. Ventral and dorsal views of a specimen of this species. Fig. 4 c. Front view of the same. Fig. 4 d. Profile view of specimen. Fig. 4 e,f. Cast of the ventral valve of a young and of a full-grown individual. Fig. 4 g. Cast of the dorsal valve of 4/. Fig. 4 h. Interior of dorsal valve, showing the brachial and cardinal processes. Fig. 4 i. Interior of ventral valve, showing the teeth and the form of the muscular im- pressions, with indistinct radiating lines below, indicating the course of the vascular impressions. Geological formation and localities. In calcareous shales of the age of the Hamilton group : at New-Buffalo, Independence, Lime creek and other places in Iowa ; Rock-island ( Illinois ), etc. Orthis iowensis, var. furnarius. PLATE II. FIG. 5. SHELL resupinate, depressed orbicular, gibbous, with a shal- low sinus in front. Ventral valve moderately convex, greatest elevation near the beak, sloping gradually to the margins, and becoming depressed in a broad undefined sinus. Dorsal valve gibbous in the middle, arched on the umbo, with the beak slightly curved over the hinge line : area narrow. SURFACE finely striated ; substance of the shell minutely punctate. [IOWA SURVEY.] 62 490 GEOLOGICAL SURVEY OF IOWA. The exterior of numerous specimens from a single locality offers little positive difference from the O. iowensis : they are less gibbous, and the sinus in front less deeply marked than in the Iowa specimens; but the form of the muscular and vas- cular impressions in the cast of the dorsal valve is so different, that I have separated these forms as a distinct variety, which may perhaps be found specifically distinct. Fig. 5. Cast of the dorsal valve. Geological formation and locality. In limestone of the age of the Hamil- ton group : Bakeoven, Illinois. Orthis ineqnalis. PLATE II. FIG. 6 a, b, c. SHELL subplano-convex, or depressed hemispherical, semi- elliptical in outline ; hinge line equalling the greatest width of the shell. Dorsal valve very gibbous, greatest convexity near the centre ; umbo prominent ; beak scarcely elevated above the hinge margin. Ventral valve nearly plain, slightly convex towards the beak, flattened at the lateral margins, and slightly concave towards the basal margin, which is not sinuate : area long, narrow ; foramen broad. SURFACE marked by alternating larger and smaller striae, and sometimes nearly equal bifurcating striae, which in the casts appear to be fasiculate near the margins : striae curved upwards on the margin of the convex valve, but not run- ning out on the hinge line. In the cast, the impressions of striae near the margin present one strong one with two or three finer ones between. This species is closely allied to one in the Chemung group of New- York, and may be identical. It differs conspicuously from O. iowensis in its longer hinge line, the nearly flat ventral valve, and absence of sinus in front. Geological formation and locality. In fine-grained sandstone of the age of the Chemung group : at Burlington, Iowa. Orthis prams. SHELL semielliptical, distorted from adhesion by the beak of the ventral valve. Ventral valve convex, gibbous towards the beak ; area high, equal the greatest width of the shell.- PALEONTOLOGY OF IOWA. 491 SURF A OP marked by fine subequal elevated striae, which are crossed by very fine well defined concentric striae and some imbricating lines of growth. This species is similar to Orthis perversa of the Hamilton group of New- York, but differs in the arrangement and character of the striae. A single ventral valve only has been observed, and it is noticed here to call atten- tion to its occurrence in Iowa. Geological formation and locality. In calcareous shales of the age of the Hamilton group : Lime creek, Worth county, Iowa. GENUS STROPHODONTA. Strophodonta : HALL, Palaeontology of New-York, Vol. ii, p. 63. SHELL depressed expanded, semielliptical, semicircular or subquadrate, transverse or elongated (external surface striated ) ; hinge line straight, usually as long as the width of the shell : ventral valve convex or concave ; dorsal valve following the curves of the opposite, often abruptly bent downwards along the middle or towards the margin ; area more or less common to both valves, more developed on the ventral valve, crenulated on the inner edges ; fissure none or partial, a linear callosity sometimes marking the centre of both areas. In the ventral valve the teeth are much reduced or nearly obsolete, a central more or less prominent bilobed process usually occupying the centre of the area in place of the triangular fissure of STROPHOMENA. Muscular impressions strongly marked, semielliptical or subreniform, separated in the middle by a depressed line, and sometimes margined by a semicircular ridge, which is an extension of the lamellae from either side. Vascular impressions foliate or flabellate, extending beyond the areas towards the base of the shell. Dorsal valve with the muscular and vascular impressions strongly marked : cardinal process bifurcate from the base, with each branch bilobed at the extremity by which it is articulated to processes beneath the area of the opposite 492 GEOLOGICAL SURVEY OF IOWA. valve, receiving between its forks the cardinal process of the opposite or ventral valve, which is bilobed or grooved for the passage of the peduncle. Entire interior surface papillose. The species of this genus have the general form of STROPHOMENA or LEPTJENA., and are similarly striated, in all the variety of simple, bifurcating and fasciculate striae. The area, which is common to both valves, is usually entire, in the species known, with the margins distinctly crenulated. There is sometimes a linear callosity along the centre of the area of each valve, in the place of the triangular foramen ; and in some specimens of L. demissa, there is a triangular space on the area of each valve, but which is solid like the other parts, and to which are affixed the cardinal processes. In some species there is sometimes a small semicircular opening at the base of the area of the ventral valve; and in one individual of another species, I have seen a triangular foramen with a round opening between the forks of the cardinal process of the dorsal valve, while the cardinal process of the ventral valve projected downwards, interlocking with the opposite one, and forming one side of the circular foramen. The muscular and vascular impressions of true STROPHODONTA are in general more like those of CHONETES or PRODUCTUS ; and are for the most part distinct from STKOPHOMENA ; while the crenulated margins and absence of triangular foramen, character of the cardinal processes, etc. furnish ready means of distinction. Strop! to dont a arcuata (n. s.). PLATE III. FIG. 1 a, b, c, and FIG. 2 a, b, e,f SHELL semielliptical ; hinge line scarcely equalling the greatest width of the shell near the cardinal extremities. Ventral valve hemispheric, gibbous in the middle, sometimes with an obtuse undefined elevation along the centre, the cardinal extremities usually a little recurved. Dorsal valve deeply concave ; area common to both valves, that of the ventral valve larger and deeply striated vertically : foramen none, or rarely an opening at the base of the area. SURFACE marked by fascicles of strong striae, or which sometimes consist of a few strong ones near the beak, bifur- cating below, while the general character of surface marking is that of strong, sharply elevated striae, with three, four or five smaller ones between : worn surface punctate or striato- punctate. Interior of shell papillose. In the ventral valve the im- pressions of the adductor muscles are small but well defined, PALAEONTOLOGY OF IOWA. 493 the vascular impressions small and margined by an elevated ridge : cardinal teeth obsolete ; cardinal process small; area indented by the bifurcate cardinal process of the opposite valve. This small species is well marked by its strong shell, extremely arcuate form, re- curved (sometimes) subauriculate hinge extremities, strongly striated area, which usually presents the entire absence of foramen, and has two deep indentations on each side of the central cardinal process of the ventral valve, which are filled by the two horns of the cardinal process of the other valve. This feature is often conspicuous when the area does not appear to have been worn. In a single individual, there is a subtriangular opening in the base of the ventral area, and a circular foramen between the forks of the cardinal process of the dorsal valve on one side, and the cardinal process of the opposite valve on the other. Fig. 1 a, b, c. Dorsal, ventral and profile view of a specimen : natural size. Fig. 2 a. Interior of ventral valve, showing the muscular and vascular impressions, the central cardinal process, and the indentations of the area made by the car- dinal process of the opposite valve. Fig. 2 b. A portion of the same enlarged, showing the parts described. Fig. 2 e,f. Enlargement of the stria; from two specimens, showing in 2/ the prevailing character, while some specimens present the features of 2 e. Geological formation and locality. In shales of the age of the Hamilton group : Lime creek above Rockford, Iowa. Strophodonta lepida (n. s.). PLATE III. FIG. 3 a. b, c. SHELL semielliptical or subquadrate, broader than long ; hinge line scarcely equalling the width of the shell. Ventral valve moderately convex, somewhat flattened towards the hinge and more abruptly curving in front, the greatest elevation being somewhat transversely along the middle. Dorsal valve moderately and uniformly concave : area principally confined to the ventral valve, striated longitudi- nally. SURFACE smooth, or marked only by a few imbricating lines of growth. Interior of ventral valve marked by strong elevated spaces for the attachment of muscular impressions, with broad fla- belliform and bilobate vascular impressions, which are limited above by a thickened margin. Interior of dorsal valve showing 494 GEOLOGICAL SURVEY OF IOWA. a few strong crenulations upon the inner edge of the area : cardinal process small ; muscular impressions subreniform, with three elevated oval spaces near the centre of the valve. Entire inner surface papillose. This species bears much external resemblance to 5. nacrea of the Hamilton group of New- York, but the internal structure is very different. Fig. 3 a. Exterior view of a ventral valve of large size. Fig. 3 b. Interior of the ventral valve, showing the muscular and vascular impressions. Fig. 3 c. Interior of a dorsal valve, showing the crenulated hinge line and muscular impressions. Geological formation and locality. In calcareous shales of the age of the Hamilton group : Rock-island, Illinois. Stropliodonta reversa (n. s.). PLATE III. FIG. 4 a - d. SHELL resupinate, semicircular or semielliptical, width greater than the length; hinge line extended beyond the width of the shell below. Ventral valve slightly convex in the middle towards the beak, flattened along the hinge and concave below, the shell being abruptly deflected near the margin. Dorsal valve flat on the umbo and slightly concave near the beak, abruptly bent downwards or almost geniculate below the centre : area common to the two valves, that of the ventral valve a little higher towards the middle ; fora- men none. SURFACE strongly striated : striae simple, strong and an- gular near the beak, and dichotomizing once, twice, or thrice before reaching the centre of the shell, increasing also by implantation. Entire surface punctate. Interior of ventral valve marked by small reniform mus- cular impressions, which are sometimes not distinctly limited : vascular impressions large flabelliform or double ovate areas, which in the upper part are defined on their margins by a thickening of the shelly matter, while ramifying linear impressions are continued to the margin of the valve : car- dinal process prominent, bilobed, with a deep depression PALAEONTOLOGY OF IOWA. 495 beneath it, and an indentation on each side in the area mar- gin, with deep pits beneath for the reception of the two horns of the cardinal process of the opposite valve. This species resembles in external markings the S. demissa, but the striae are stronger and more angular towards the beaks. The resupinate form and abruptly deflected margins distinguish it from other species. This one and the preceeding species show the indented outline of the cardinal area, produced by the impressions of the cardinal process of the opposite valve. Fig. 4 a. Dorsal view of a specimen having the margin somewhat irregularly plicated, which is apparently due to accident during the life of the animal. Fig. 4 b. Ventral view of the same. Fig. 4 c. Profile view. Fig. 4 d. Interior of ventral valve, showing the indented margin of area, bilobed cardi- nal process, the muscular and vascular impressions. Geological formation and locality. In calcareous shales of the age of the Hamilton group : Lime creek above Rockford, Iowa. PLATE III. FIG. 5 a- fc. Strophomena demissa : CONRAD, Journal Academy Natural Sciences, Philadelphia, 1842, Vol. viii, pa. 258, pi. 14, f. 14. Strophodonta demissa : HALL, Report of the Regents of the University of New-York, upon the State Collections of Natural History, for 1856, p. 137. SHELL seinielliptical, usually wider than high ; hinge line usually equalling or greater than the width of the shell below, the extremities often prolonged into mucronate tips, and sometimes the margins are contracted below, giving a subauriculate character to the shell. Ventral valve very re- gularly convex, sometimes gibbous or ventricose : area well defined, strongly striated vertically, the inner margin cre- nulate. Dorsal valve regularly concave, and following the curvature of the opposite valve : area sublinear, common to both valves ; inner edges strongly crenulate. SURFACE marked by strong subangular striae, which are several times dichotomized before reaching the base of the shell, and varying considerably in number and strength in different individuals. Fine concentric strise mark the surface of well-preserved specimens, and, under a lens, the entire surface is punctate. 496 GEOLOGICAL SURVEY OF IOWA. The description above applies to the Iowa specimens; while those of New-York, which are regarded as identical, present some differences. The shell in the latter is usually stronger, and more convex on the ventral valve, while the dorsal valve is often nearly flat in its upper half, and bent upwards towards the margin : the area is likewise broader, being nearly double the width; the cardinal extremities less salient, and the stride more subdivided and finer in the middle and lower parts of the shell. Having no specimens from Iowa which show the interior structure, I have illu- strated these parts from specimens from the Hamilton group of New- York. Fig. 5 a, b. Ventral and dorsal views of a specimen of ordinary form and size, from Iowa. Fig. 5 c. A specimen where the cardinal extremities are more salient. Fig. 5 d. Profile showing the convexity of the specimen. Fig. 5 e. Interior of the ventral valve of a specimen from New-York, showing the bilobed cardinal process in the centre of the area, and the muscular and vascular impressions. Fig. 5/. Enlargement of the area surface, showing the deeply striate character. Fig. 6 g. Interior of the dorsal valve of a specimen from New-York, showing, the mus- cular impressions and the double cardinal process. Fig. 5 h. The same enlarged, showing the crenulate dental lamella on each side of the base of the cardinal process. Fig. 5 i. Enlargement of a portion of the area and cardinal process of the dorsal valve, looking from the outside. In this individual there are no prominent crenulated lamellae, as in fig. 5 h. Fig. 5 /c. A similar view of another individual, showing, at the base of the cardinal pro- cess, the indentations made by the two lobes of the process from the ventral valve, and the lateral crenulated lamella?. Geological formation and localities. In calcareous shales of the age of the Hamilton group of New- York : New-Buffalo, Pine creek, Independence, Lime creek, and other places in Iowa; Rock-island (Illinois), and in the shales of the Hamilton group in Erie county, New- York. Strophodonta fragilis. PLATE III. FIG. 6 a, b, c. Strophodonta fragilis : HALL, Report of the Regents of the University of New-York, on the State Collections of Natural History, for 1856, p. 143. SHELL thin, fragile, semielliptical, usually wider than high; hinge line extending beyond the width of the shell below, and the margins often abruptly contracted just beneath the cardinal extremities. Ventral valve very slightly convex, or nearly flat. Dorsal valve flat or scarcely concave : area entire, very narrow, linear, almost entirely confined to the ventral valve, striated vertically, and crenulated on the inner mar- gins throughout its entire length. PALEONTOLOGY OF IOWA. 497 SURFACE covered by slender closely arranged radiating striae, crossed by finer elevated concentric lines which be- come more prominent on the radiating striae of the ventral valve, giving a minutely nodulose or granulose character to the entire surface when well preserved. The radiating striae of the dorsal valve are more evenly rounded, and increase mainly by bifurcation ; while those of the opposite valve increase by interstial additions ( this character may be sub- ject to variation), and are crossed by even, raised, concentric lines which produce no granulations on the surface. Internally the ventral valve shows a very small, scarcely conspicuous central cardinal process. The muscular impres- sions are usually slightly marked, and the vascular impres- sions double, foliate or flabellate, with a scarcely defined separating ridge, and margined by a slight elevation of the lamellae proceeding from the hinge line. This species may be recognized by its extreme tenuity and the narrow space between the two valves, which scarcely exceeds the thickness of the shell. The area presents no appearance of a triangular foramen or a deltidium, though there is sometimes a slight sinuosity in the margin. In the New- York specimens, the central cardinal or dental process of the ventral valve is conspicuous, while in the Iowa specimens it is very subdued. The Iowa specimens occur chiefly as single valves, the ventral valve only being usually preserved, while rarely there occur specimens re- taining the two valves. Fig. 6 a. View of the ventral valve. Fig. 6 b. Interior of ventral valve, showing the foliate vascular impressions, entire area, etc. Fig. 6 c. Enlargement of the striae. Geological formation and localities. In calcareous shales of the age of the Hamilton group of New-York : New-Buffalo and Independence in Iowa, and Rock-island in Illinois. Productus dissimilis (n. s.). PLATE III. FIG. 7 a, b, c, d e. SHELL semielliptical in outline ; length and breadth nearly equal. Ventral valve extremely convex, 'gibbous in the mid- dle and towards the beak ; umbo elevated above the hinge line ; beak incurved ; hinge extremities slightly auriculate. [ IOWA SURVEY.] 63 498 GEOLOGICAL SURVEY OF IOWA. Dorsal valve deeply concave, following the curvature of the opposite valve : a small space or area ? between the margins of the two valves, along the hinge line. SURFACE of ventral valve marked by fine radiating striae and a few concentric imbricating lines of growth, which become wrinkles on the cardino - lateral margins : a few scattered nodes, or bases of tubular spines mark the surface at irregular intervals. Dorsal valve marked by regular con- centric imbricating lines, without visible radiating striae. This species is proportionally narrower than any of the Productidese (which I know) in the rocks of this age, and the strongly marked difference in the character and direction of the striae on the two valves is a very characteristic feature of the shell. In general form and the character of the striae of the ventral valve, it bears some resemblance to P. undiferus of DE KONINCK, but the concentric striae of the dorsal valve are quite distinctive. Fig. 7 a, b. Dorsal and ventral views of the. shell. Fig. 7 c. Profile of the same. Fig. 7 d. Enlargement of the striae from the surface of the ventral valve. Fig. 7 e. Enlargement of concentric striae from the surface of the dorsal valve. Geological formation and locality. In calcareous shales of the age of the Hamilton group : Lime creek above Kockford, Iowa. Productus pyxidatus ( n. s.). PLATE III. FIG. 8 a - e. SHELL semielliptical, breadth greater than the height ; cardinal extremities somewhat rounded, the hinge line being shorter than the greatest width of the shell. Ventral valve broadly convex, somewhat flattened and a little recurved at the cardinal extremities, gibbous on the umbo and beak re- curved. Dorsal valve broadly concave, a little flattened at the cardinal extremities ; concavity less than the convexity of the opposite valve. SURFACE marked by close concentric striae, and more con- spicuous imbricating lines of growth : the ventral valve sometimes having elongated spiniferous tubercles or ridges, which are arranged in alternating series ; the dorsal valve sometimes with indistinct radiating ridges, which are not spiniferous. PALAEONTOLOGY OF IOWA. 499 The prevailing character of the species, in its surface markings, is that of a con- centric imbricating or larnellose structure; while in some specimens we have, in addition to this, the elongate spiniferous tubercles towards the umbo, and elongate ridges in the lower part of the shell. There is no visible area in several specimens examined, when the two valves and hinge line are entire; and the interior of the dorsal valve shows a strong bilobed cardinal process, without sockets for the cardinal teeth of the opposite valve as in true STROPHALOSIA. Fig. 8 a. Ventral valve, showing a few spiniferous tubercles on the upper part of the valve, while the ridges which usually characterize the lower part in such spe- cimens are not perceptible. This specimen is proportionally narrower than the prevailing forms. Fig. 8 b. Ventral valve of the ordinary form, without spiniferous nodes or ridges. Fig. 8 c. Dorsal valve of another individual, with some undefined radiating ridges upon the surface. Fig. 8 d. Profile view of a specimen. • Fig. 8 e. Interior of a dorsal valve, showing the cardinal process, muscular impressions, etc. Geological formation and localities. In calcareous shale and in limestone of the age of the Hamilton gi*oup : Hamburgh (Illinois), and Louisiana ( Missouri )*. Productus slmniardianus ( n. s.). PLATE III. FIG. 9; and PLATE VII. FIG. 1. SHELL semielliptical, wider than long ; hinge line about equal to the width of the shell. Ventral valve very convex, gibbous in the middle and towards the umbo ; beak incurved. Dorsal valve moderately concave ; extremities flattened, subauriculate. SURFACE marked by fine concentric striae and strong spi- niferous tubercles, which are sometimes crowded near the cardinal extremities of the ventral valve. This species has been referred to P. subaculeatus and P. murchisoniamis ; but it differs from the former in the smaller and less rounded character of the bases of the spines, and from the latter in its smaller size, less numerous and less regularly ar- ranged spiniferous tubercles, and the absence of the strong radiating ridges shown in the figures of the dorsal valve. Fig. 9. The interior of a dorsal valve, showing the marks of the spiniferous ridges upon the inner surface. * At the time these specimens were figured, I regarded certain other forms from near Burlington ( Iowa) as identical with them : a farther comparison, however, shows the propriety of separating these specimens from those of that locality. 500 GEOLOGICAL SURVEY OF IOWA. PLATE VII. Fig. 1. The ventral valve of the same species. Geological formation and localities. In limestone of the age of the Ha- milton group, at Clarkesville (Missouri); and in the fine sandstones of the age of the Chemung group, at Burlington ( Iowa ). Productus snbalatus (n. s.). PLATE III. FIG. 10 a, b, c. SHELL semielliptical or semicircular, usually much wider than high ; hinge extremities equalling or less than the width of the shell. Ventral valve ventricose in the middle, gibbous on the umbo and towards the beak, extended, flat- tened and auriculate at the hinge extremities ; beak incurved over the hinge line. SURFACE marked by fine concentric undulating strise, and towards the lateral margins by strong wrinkles, and orna- mented by numerous round tubular spines which are often somewhat crowded near the cardinal margin on each side of the beak, and sometimes arranged in a continuous line upon the umbo : towards the beak the spines are smaller, and become stronger towards the margins of the shell. The shell is often unsymmetrical, one of the ears being much more extended than the other, and sometimes both are so much extended as to have an alate appearance. The character of the spines, or the bases which usually remain, bear some resem- blance to P. subaculeatus ; but they are less regularly disposed, and the shell is re- markably distinct from any other species in our rocks, so far as I know. • Fig. 10 o. Ventral valve of a specimen of medium size, with few spines, and preserving the usual characteristics of the species. Fig. 10 b. Ventral valve of a larger specimen, showing the irregular distribution of the spines. Fig. 10 c. Profile view of fig. 10 b. Geological formation and locality. In calcareous shales of the age of the Hamilton group of New- York : Rock-island (Illinois), opposite Daven- port (Iowa). PALAEONTOLOGY OF IOWA. 501 Spirifer hungerfordi (n. s.). PLATE IV. FIG. 1 a - k. SHELL inequi valve, semielliptical, transverse or elongated, varying with the age of the animal. Dorsal valve regularly convex, the greatest convexity above the middle, and curv- ing gently on all sides ; beak incurved slightly beyond the hinge line : no defined mesial fold. Ventral valve in the young and half grown shells semielliptical, gibbous above the middle, having twice as great an elevation as the oppo- site valve, the beak much extended above the hinge line and slightly incurved ; hinge line equalling or extending beyond the width of the shell ; sinus shallow, scarcely de- fined above the middle, and producing a slight sinuosity in front : area large and well defined, principally confined to the ventral valve and limited by an obtuse margin, striated vertically ; foramen narrow, acute above, and extending quite to the apex of the shell, the margins or dental lamellae often a little thickened or projecting. SURFACE marked by fine simple radii, a few only of which dichotomise on the mesial sinus and elevation, and rarely on other parts of the shell. Radii about equal to the spaces between them, and both are again finely striated in the same direction by microscopic lines, and the whole crossed by fine concentric striae which give a granulate appearance to the unworn surface. In old shells, the proportions of length and breadth vary so that they become longer than wide, the hinge line and area are less than the greatest width of the shell, the valves become more gibbous, the beak of the ventral valve more incurved, and the area contracted : at the same time the sinus becomes better defined towards the base, the mesial fold distinctly elevated towards the margin, and the radii more strongly developed. 502 GEOLOGICAL SURVEY OF IOWA. This species bears much resemblance to the Spirifer pachyrynchus of DE VERNEUIL (Russia and the Ural mountains, pa. 142, pi. iii, f. 6); but the area in that species is smaller and more contracted at its upper margins, particularly in old shells, which are also quite free from striae. Fig. 1 a, b. Dorsal views of two individuals, showing the form of shell, proportion of area, etc. Fig. 1 c, d. Ventral views of two individuals. Fig. 1 e. Profile view of 1 b. Fig. If. Front view, the ventral valve being above. Fig. 1 g, h. Dorsal and profile views of an old shell. Fig. 1 i. Ventral view where the shell has been ground off to show the internal spires. Fig. 1 ft. Interior of the ventral valve, showing the foramen and dental lamellae which extend downwards to the middle of the shell. Geological formation and locality. In calcareous shale of the age of the Hamilton group : Lime creek above Rockford, Iowa. Spirifer wliitneji (n.s.). PLATE IV. FIG. 2 a, b, c, e. SHELL of medium size, transverse, semielliptical or penta- gonal ; height and width about as three to four. Ventral valve gibbous towards the beak and curving abruptly to the base ; beak elevated above ;hat of the opposite valve, and incurved over the area : mesial sinus well defined at its margin by stronger plications, curvilinear or subangular, beginning at the beak and regularly deepening towards the base, where it is often produced in a rounded or angular projection. Dor- sal valve gibbous in the centre, and sloping abruptly to the sides ; mesial fold elevated, prominent, rounded and well defined, sometimes subangular ; beak incurved ; hinge line equal to or exceeding the width of the shell : area mode- rately large, concave, vertically striated ; a narrow defined area on the dorsal valve : foramen broad at base and open to the summit ; a narrow defined groove marks the junction of the dental lamellae with the area. SURFACE of the mesial elevation and sinus marked by dichotomizing striae, of which twelve to fifteen may be seen on the margin, and three or four at the summit ; lateral por- tions of the shell marked by twenty-four to thirty slender PALJEONOLTOGY OF IOWA. 503 simple rounded plications on each side, which are larger than those in the mesial sinus and elevation ; these gradually diminish in size, till they become extremely slender on the extremities of the shell : depressions between the plications narrower than the plications themselves, except those bor- dering the mesial fold, which are broader and deeper than the others. Entire surface marked by extremely fine radiating striae, which cover alike the plications and the spaces between them : these sometimes give the plications a grooved ap- pearance under a lens. Equally slender concentric undu- lating striae mark the whole surface; and along these are arranged minute granulations, which are only visible under a lens : a few more distinct imbricating lines of growth are sometimes seen. This species bears a close resemblance to Spirifer archiaci of MURCHISON, as described and figured in the Geology of Russia and the Ural mountains, Vol. ii, pa. 155, pi. iv, f. 5 a, b, c ; and by DE KoffusrcK, Descriptions des Animaux fossiles de Belgique, pa. 254, pi. xiv, f. 5; but our specimens do not show the variety of form observed in the European species. A comparison of several specimens shows that the plications, as well as the mesial sinus and elevation, are more angular, and the foramen narrower in the European than in the American specimens, while the former still retain some remains of fine radiating striae. In the American specimens the plications are directed towards the beak, a few of the outer ones only running out upon the hinge line ; while in the European specimens a larger number of plications terminate on the hinge line before reaching the beak. These differences, which are perhaps too slight to be generally regarded as deserving of specific distinction, are, nevertheless, of importance when regarded in connection with the wide geographical separation of the Russian, Belgian and Iowa specimens, and the absence of knowledge regarding the exact parallelism of the deposits in the two countries. Fig. 2 a, b. Ventral and dorsal views of a specimen of medium size. Fig. 2 c. Cardinal view of the same. Fig. 2 e. Enlargement, showing fine striate and granulose surface. Geological formation and locality. In calcareous shales of the age of the Hamilton group : Lime creek above Rockford, Iowa. 504 GEOLOGICAL SURVEY OF IOWA. Spirifer submucronatus ( n. s.). PLATE IV. FIG. 3 a, b, c. Spirifcr indct. : OWEN, Report on Wisconsin, Iowa and Minnesota, pi. iii, f. 9. SHELL small, somewhat semicircular, gibbous in the middle ; the hinge line variable in length, often extending into mu- cronate points. Ventral valve gibbous towards the beak, abruptly sloping towards the front and sides ; mesial sinus deep, subangular. Dorsal valve moderately convex, some- times a little gibbous, and often nearly flat ; mesial fold strongly elevated and flattened on the summit : area mode- rately high, and in some specimens proportionally higher than in others. SURFACE marked by eight to twelve or more strong abrupt or subangular plications on each side of the mesial fold or sinus ; mesial fold flattened or a little depressed in the centre, and an incipient fold in the bottom of the sinus. In well preserved specimens the surface is marked by sharp elevated concentric laminae which arch abruptly upwards on the plications, and which undulate on the mesial fold and sinus corresponding to the line of depression and elevation. This species bears much resemblance to the S. mucronatus of the Hamilton group of New-York, and is often mistaken for that species; but all the specimens which have fallen under my observation are much smaller; the plications are more elevated, and often flattened upon the summit ; the imbricating lamellae are stronger, more closely araanged and more arched, while the area is proportionally higher. This species is apparently identical with that figured by Dr. D. D. OWEN, pi. iii, f. 9, cited above ; since I know of no other similar species occurring in the locality named by him. Fig. 3 a, b. Dorsal and ventral valves of a specimen having one hinge extremity more produced than the other. Fig. 3 c. Cardinal view of the same specimen. Geological formation and locality. In calcareous shales of the age of the Hamilton group of New- York : at Independence, New-Buffalo and Rock- ingham (Iowa), and Rock-island (Illinois). PALAEONTOLOGY OF IOWA. 505 Splitter iimtilis (n.s.). PLATE IV. FIG. 4 a, b, c. VENTRAL valve semicircular or subpentangular, gibbous in the middle and towards the beak ; cardinal extremities somewhat produced ; beak short, scarcely incurved ; mesial sinus deep, strongly defined at the margins, curved in the bottom. Area moderately high, abruptly concave, defined above by a sharply angular margin ; foramen narrow, reach- ing to the beak, with a pseudo-deltidium. SURFACE marked by twelve or more strong rounded plica- tions, which rapidly decrease in size as they recede from the mesial sinus ; plications crossed by fine concentric un- dulating lamellae. This species differs from the last in the greater elevation of the beak, the shorter hinge extremities, and the sinus without indications of a central fold. The character of the plications, or concentric lamellae, offers no important differences from Spirifer submucronatus. Fig. 4 a. View of the ventral valve. Fig. 4 b. Cardinal view, showing the area and foramen. Fig. 4 c. Enlargement of the surface of fig. 4 a. Geological formation and locality. In calcareous shales of the age of the Hamilton group : Independence, Iowa. • Spirifer fimbriatus. PLATE IV. Fio. 5 a - e. D elthyris fimbriata : CONRAD, Jour. Acad. Nat. Sciences, Vol. viii, p. 263. Spirifer (n. s.l) : OWEN, Report on Wisconsin, Iowa and Minnesota, pi. iii, f. 7. SHELL transversely subelliptical : valves often almost equal- ly convex ; hinge line less than the width of the shell ; ex- tremities rounded. Ventral valve transversely elliptical, with the upper part and the umbo round, prominent and very gibbous ; beak incurved : area high and short, the exterior of the shell encroaching largely upon the space within the beak ; foramen very large ; mesial sinus rounded, shallow. Dorsal valve most convex in the middle ; beak and margin [ IOWA SURVEY.] 64 GEOLOGICAL SURVEY OF IOWA. of the shell slightly arching over the area ; mesial fold broadly rounded, moderately elevated, and defined on each side by a groove broader than those between the plications. SURFACE marked by from four to six ( often three in young specimens) rounded and very moderately elevated plications which are separated by shallow depressions between, the whole becoming obsolete before reaching the beak and hinge line ; concentrically marked by fine closely arranged striae and more distant imbricating lamellse, upon the edges of which are arranged, in regular concentric undulating lines, short longitudinal elevated striaa, or more properly the elon- gated bases of minute semitubular spines, which ornament the lower edges of each successive imbrication, and are formed by the contraction and separation of the extended edges of the lamellae. This is the only species to which I can refer the description given by Mr. CONRAD of Delthyris jimbriata. The species occurs in the Upper Helderberg limestone and in the Hamilton group of New- York; and I have seen a specimen of, apparently, the same species in the Oriskany sandstone. The western specimens are usually smaller than those of New- York ; though the one figured by Dr. OWEN, pi. iii, f. 7, is equal in size to the larger specimens observed in any localities. There are rarely six, and still more rarely seven, defined plications upon each side of the mesial fold and sinus : commonly there are no more than four, sometimes two or three, and in one specimen of more than half- an inch in diameter there are no defined plications. In rare examples the plications are defined nearly or quite to the beak. The short semitubular spines are rarely preserved, though the bases are well marked. In the absence of external characters, the elliptical form of the shell, with the broad round plications, even in casts, will generally serve to distinguish the species. Fig. 5 a. A fragment of a ventral valve, in which the sinus is subangular. Fig. 5 b. Cardinal view of the same, showing the broad foramen which occnpies a large part of the area. Fig. 5 c. Dorsal valve of a small individual, preserving the spiniferous bases. Fig. 5 d. Profile view of a small specimen from the Hamilton group of New-York. Fig. 5 e. Enlargement of the surface as it usually appears when the bases of the spines are preserved. Geological formation and localities. In calcareous shales of the age of the Hamilton group of New- York : Davenport, New-Buffalo ( Iowa ); Rock- island ( Illinois ). PALEONTOLOGY OF IOWA. 507 Spirifer bimesialis (n.s.). PLATE IY. FIG. 6 b, c, d. SHELL extremely transverse ; width more than twice the length of the shell; hinge line extremely extended and produced into mucronate points ; front emarginate. Ventral valve gibbous in the middle, curving to the front, and slop- ing gently towards the lateral extremities, where it is nearly flat ; beak much elevated above the opposite valve and very slightly incurved ; area concave, moderately high, and much extended laterally ; sinus strongly defined, subangular, with a simple plication in the bottom. Dorsal valve less elevated than the opposite, convex in the middle, curving towards the beak ; mesial fold divided by a slight depression along the centre, and emarginate in front for the reception of the mesial extension of the opposite valve. SURFACE marked by about twelve or thirteen, or more, simple plications on each side of the mesial fold and sinus : plications abruptly rounded on the upper side, crossed by closely arranged imbricating lamellose striae which are ab- ruptly arched on the plications and in the mesial sinus, while they are doubly arched upon the mesial fold. This species bears considerable resemblance to 5. submucronatus, fig. 3 ; but the specimens are less gibbous, and the cardinal extremities less abruptly but more ex- tremely extended. It bears some resemblance to S.muralis (Ds VERNEUIL, Russia and the Ural mountains, pa. 171, pi. v, f. 5); but the hinge extremities are less ab- ruptly mucronate, the area less high, and the mesial fold double or depressed in the middle. Fig. 6 b. Dorsal valve of an apparently full-grown specimen. Fig. 6 c.- Cardinal view, showing the area, foramen, and part of the dorsal valve. Fig. 6 d. Ventral valve of another specimen, showing the small plication in the centre of the mesial sinus. Geological formation and locality. In calcareous shales of the age of the Hamilton group : Independence, Iowa. 508 GEOLOGICAL SURVEY OF IOWA. Spirifer aspera ( n. s.). PLATE IV. FIG. 7 a, b, c, d. SHELL semielliptical, width about twice the length ; hinge line equalling the greatest width of the shell, and abruptly angular at the extremities. Ventral valve triangular pyra- midal, extremely elevated at the umbo, and sloping abruptly to the lateral and anterior margins ; mesial sinus shallow, strongly denned at the edges, sides straight, flattened with- in, sometimes curvilinear : area straight and flat, abruptly defined at its margins, equal or less in height than the length of the valve, transversely and vertically striate ; foramen proportionally narrow, extending to the beak, and partially closed within by a pseudo-deltidium ; beak not incurved. Dorsal valve nearly flat or moderately convex ; mesial fold strongly defined at the margins, and rounded above. SURFACE, in full-grown specimens, marked by twenty or more simple rounded and moderately elevated plications on each side of the mesial fold and sinus. Plications often fifteen to eighteen in ordinary specimens, four or five only of which reach the beak, the others running out along the hinge line and margins of the area ; concentrically marked by fine imbricating lines of growth, which are sometimes very con- spicuous. Entire surface granulose ; granules closely arranged, sometimes visibly following the concentric strise, and in other parts apparently scattered without order. This species approaches in form the S. macronotus of the Hamilton group of New- York, and may be regarded as its western representative. This one differs in its less cardinal extension, more abrupt elevation of the ventral valve and proportionally higher area, fewer plications and granulose surface. It bears a close resemblance in form to the «S. tenticulum ( MURCHISON and DB VERNEUIL, Russia and the Ural Mountains, pa. 159, pl.v, f. 7); but the sinus of that species is plicated. Fig. 7 a. Ventral valve of a specimen less than the full size. Fig. 7 b. Cardinal view of the same, showing the area and foramen, which is partially filled with the pseudo-deltidium. Fig. 7 c. Dorsal valve of a larger individual, which shows about twenty strue on each side of the mesial fold. Fig. 7 d. Enlargement of the surface, showing the granulose character, with a few dis- tinct imbricating lines. PALAEONTOLOGY OF IOWA. 509 Gco^gical formation and localities. In calcareous shale of the age of the Hamilton group : Independence ( Iowa) ; Rock-island ? ( Illinois). Spirifer parryaims ( n. s.). PLATE IV. FIG. 8 a, b. SHELL subglobose, transversely subelliptical ; cardinal ex- tremities usually rounded ; valves almost equally convex. Ventral valve gibbous in the middle and on the umbo ; beak slightly incurved ; mesial sinus well defined from the beak and broadly expanded below, with the margins less strongly defined, curvilinear within : area high, extending to the hinge extremities, and limited by a sharp angle above ; foramen large, and open to the apex of the shell. Ventral valve very gibbous in the middle, strongly arcuate towards the baso-lateral margins, and abruptly curved at the umbo ; mesial sinus prominent, rounded, much elevated and deeply emarginate in front for the reception of the projecting mesial extension of the opposite valve. SURFACE marked by about seventeen, eighteen or more simple broadly rounded and little elevated plications on each side of the mesial fold and sinus, which are separated from each other by very narrow shallow grooves. In perfect specimens, the entire surface of plications and mesial fold and sinus are covered by extremely minute radiating strise, and crossed by equally fine concentric striae and a few im- bricating lines of growth. This species bears considerable resemblance to the S. granulifera of the Hamilton group of New- York, but it is a smaller shell, the mesial fold is not depressed in the centre, and there is no elevation in the sinus as in that species; while in well pre- served specimens, the granulose surface of the one, and the finely striated surface of the other, contrast sufficiently to afford a ready means of distinction. The S. granulifera is not known in the Mississippi valley up to this time. The S. eatoni and S. clintoni of the Hamilton group of New- York resemble this shell in some respects. Fig. 8 a. Dorsal view, showing the beak of the ventral valve, the area in part, with the foramen projecting beyond the hinge line of the dorsal valve. Fig. 8 b. Ventral valve of the same specimen. Geological formation and locality. In calcareous shale of the age of the Hamilton group of New-York : New-Buffalo, Iowa. 510 GEOLOGICAL SURVEY OF IOWA. Spirifer pennatus, PLATE V. FIG. 1 a - i. Spirifer pennatus and S. ligus : OWEN, Geological Report of Wisconsin, Iowa and Minnesota, pa. 585, pi. iii, f . 3, 4 and 8. SHELL variable in form from subglobose to transverse and broadly triangular, often inequilateral ; hinge line extremely extended into wing-like expansions ; valves often nearly equally convex. Ventral valve very gibbous in the middle and on the umbo ; beak much elevated above the hinge line, more or less pointed and slightly incurved ; mesial sinus strongly defined at the margins, widely spreading towards the base, and produced in an angular extension in front : area concave and very large, extending to the extremities of the hinge line, striated vertically and longitudinally ; foramen large, open to the apex, and forming an equilateral triangle. Dorsal valve very gibbous in the middle and upon the umbo, which is abruptly incurved, regularly curved to- wards the baso-lateral margins, and more or less compressed towards the lateral extremities ; mesial fold strongly ele- vated, sometimes a little flattened on the top, and often subangular towards the front and slightly depressed on each side. SURFACE marked by about fourteen to twenty-six or more rounded plications on each side of the mesial fold and sinus; those near the centre, to the number of ten or twelve, being much stronger than those upon the extremities, which be- come finally very slender. Plications crossed by closely ar- ranged concentric undulating laminae of growth ; and the entire surface, in perfect specimens, ornamented by slender radiating striae, which become granulose at their junction with the concentric striae. This species presents considerable variety of aspect and of surface marking; but after examining a large number of specimens from Rock island, New-Buffalo and Independence, I cannot find means of separation, and am compelled to regard for the present the S. pennatus and