This shell can usually be readily distinguished by its widely expanded outer volution, the broad, shallow sinuosity in the anterior margin of the lip, and the absence of all markings on this part of the shell except striæ of growth. The prominent posterior part of the volution has more or less strongly defined costa parallel to the striæ of growth. In some specimens this is scarcely a conspicuous feature; in others it is limited to so small a portion of the volution as hardly to be seen when looking directly upon the surface, as the fossil is usually imbedded in the rock with the mouth downward. There is also great variation in the size of these costa, which in some specimens are twice as strong as in others, and the spaces between them two or three times as wide as the elevated portions; while in other examples they are reduced to regular equal striæ: and in all cases they gradually become obsolete by merging into the ordinary surface striæ. These phases are illustrated in figures 17-23. In most of the specimens examined, the expanded portion of the volution has been broken off, and there remains only the strongly marked portion of the surface. The removal of the shell leaves a smooth cast of the interior. In all the specimens determined, the margin of the lip is found to be slightly recurved. The expanded margin of the aperture extends around the posterior part of the volution, nearly inclosing it, as shown in figures 17-19; and more especially on looking upon the interior, as shown in figures 27 and 28, where the margins are nearly conjoined on the posterior side. This expanded lip is usually recurved and thickened in the umbilical region, the heavy callus extending more or less completely over the posterior part of the volution. At the sides this callus is smooth, but in the central portions it is elevated and pustulose, following the convexity of the volution, and gradually extended outward from the aperture and forward on the volution. It sometimes nearly closes across the area, but usually leaves a free space or sinus where the transverse costæ remain visible, while the pustulose callus extends forward on each side, as shown in figures 22, 23, 27-29, and also in figures 5 and 6 of plate 24. In many examples, the pustules upon the callus appear to have no regular order, but as a rule they are arranged in lines corresponding to the arching coste over which the callus lies. This is especially marked in figure 8, plate 24. Rare examples are seen where the callus scarcely extends beyond the thickened margin at the edge of the aperture, while the pustules are already implanted upon the arching costæ, and the spaces between them are gradually becoming undefined or obsolete. The pustules are often elongate, extending across two or more of the costa, as seen in figure 7, plate 24. These phases in the extension of the callus are shown in figures 27-29 of plate 22, and in figures 6-8 of plate 24. In a single longitudinal section the thickened columellar lip is shown, as in figure 30 of plate 22, and more extremely on plate 26. In its general expanded form this species resembles the B. Leda and B. Lyra, but differs in the external markings. It has also the same general form as B. rudis of the Hamilton group, and B. trilirata of the Chemung group, but in the former the strong distant costa with distinct revolving striæ or ridges are marked characters; while the tricarinate aspect of the other, together with the revolving striæ are distinguishing features. In its arching costæ it closely resembles the B. Newberryi; but in that species the volution is more depressed on the back, with the callus of the columellar lip smooth, and extending almost directly across the volution. Nearly all the specimens examined are more strongly striate on the back of the volution, near the expansion, than the one figured in the Geological Report of the Fourth District; but in other respects there is no important difference. In the prevailing forms of this species the aperture measures, in the transverse diameter, from one inch and five-eighths to one inch and six-eighths, and in the longitudinal direction about one inch and a quarter. Larger specimens have a transverse diameter of aperture of two and a quarter to two and a half inches, with a dorso-ventral diameter of about two to two and a half inches. Formations and localities. In the coarse shales of the Hamilton group in Schoharie county; in Otsego, Onondaga and Chenango counties; on the shores of Skaneateles, Cayuga, Seneca and Canandaigua lakes, and in the ravines entering those lakes; more rarely at York in Livingston county; and in the soft calcareous shales on the shore of Lake Erie at Eighteen-mile creek. It is not rare in the form of casts near Cumberland, Md. It occurs in the limestone above the hydraulic beds at the Falls of the Ohio.* BELLEROPHON RUDIS. PLATE XXIV, FIGS. 13, 14, 15. Bellerophon rudis, HALL. Descriptions of New Species of Fossils, etc., p. 29. 1861. 66 66 66 66 66 64 Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 57. 1862. SHELL extremely ventricose, the inner volutions rounded and subglobose; umbilicus small; the last half of the body-volution abruptly expanded, and the peristome spreading almost rectangularly to the axis of the shell. Anterior margin of the peristome slightly sinuous, and spreading on the posterior side over the preceding volution. The upper part of the last volution is marked by strong transverse arching costa, which are closely arranged on the summit of the volutions, but towards the aperture, become irregular, stronger and more distant: the expanded portion of the volution has two, three or more strong folds or wrinkles parallel to the margin of the peristome, which are stronger in the middle, and become obsolete on each side: the upper part and sides of the volution are marked by longitudinal ridges which reach nearly to the margin in front, but in some parts are irregular and obscure; this feature is subject to great variation, being in some specimens scarcely perceptible. This shell resembles in form the B. patulus, but is more robust, and the transverse costæ fewer and stronger; the concentric folds on the expanded portion, as well as the longitudinal ridges on the sides, are distinguishing characters. In one specimen the transverse diameter is about one inch and seven-eighths, and the longitudinal diameter nearly one inch and three-fourths. The general proportions are so nearly like B. patulus that it might perhaps be *For information regarding the age of this limestone at the Falls of the Ohio, heretofore referred to the Upper Helderberg group, see note at the end of descriptions of the Gasteropoda. 1 regarded as an extravagant form of the same, marked by peculiar developments of the surface characters. In the best preserved specimen before me, the summit of the volution near the aperture is marked very nearly as in the more strongly costate forms of B. patulus; but receding from the summit the costæ become stronger and farther separated from each other, with strong revolving ridges, or coarse striæ coming between them. These last, though becoming obsolete, can be traced to the margin of the shell. The few specimens of this species observed show considerable variation in the external features, which are illustrated in figures 13, 14 and 15 of plate 24. In the broad anterior expansion and concentric rugæ this species resembles some forms of B. triliratus of the Chemung group; but the absence of carinæ and of the fine revolving striæ offer a characteristic distinction. In the broad anterior expansion of the peristome the B. patulus and B. rudis resemble PHRAGMOSTOMA, to which genus, in the absence of positive knowledge of the interior, I had at one time doubtfully referred them. They are, however, true BELLEROPHON. Formation and locality. In the coarse shales of the Hamilton group, at Fultonham, Schoharie county, N. Y. BELLEROPHON OTSEGO. PLATE XXIV, FIG. 12. Bellerophon Otsego, HALL. Descriptions of New Species of Fossils, etc., p. 32. 1861. 66 66 66 66 Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 60. 1862. SHELL rotund, subglobose; body-volution ventricose, somewhat trilobate, the middle much wider than the lateral lobes, gradually spreading towards the aperture, which apparently is moderately expanded and sinuate in front. The lateral lobes are separated from the central part of the volution by a well marked sinus, and this character, with the comparatively wide dorsal band, limited by thin sharp striæ, are characteristic features. SURFACE marked by fine, regular, transverse, arching striæ, having a retral curve upon the dorsum, which is traversed by a comparatively wide band, inclosed between two sharply elevated striæ, distant from each other about one line. Formation and locality. In the coarse sandy shale of the Hamilton group, in Schoharie county, N. Y. BELLEROPHON THALIA. PLATE XXV, FIGS. 1, 2, 3. Bellerophon Thalia, HALL. Descriptions of New Species of Fossils etc., p. 32. 1861. 66 66 86 66 66 Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 60. 1862. SHELL ovoid or subspheroidal. Volutions rotund, the last one gradually expanding for half its length, becoming ventricose and abruptly spreading toward the aperture, which is somewhat orbicular, with a deep sinus at the anterior margin; umbilicus exposed. SURFACE marked by extremely fine, even, concentric striæ, bending abruptly backward on the dorsum, which is marked by a sulcate carina. This species occurs as casts of the interior, or specimens from which the shell has been mostly removed by maceration and solution. Portions of the shell remaining show a surface-marking similar to B. bilobatus of the Lower Silurian rocks, and the shell has nearly the same form and proportions, with the exception of the banded dorsum, which is distinctly limited on each side by a sharply elevated line, and is always more or less well-preserved in the casts, when all the other surface-markings have disappeared. In general form this species bears much resemblance to B. Pelops; but the volution is more abruptly expanded near the aperture; the sides are obtusely subangular, and curving into a distinct umbilicus; the dorsal band is more conspicuous and distinctly sulcate or bicarinate; the sinus in the peristome is deeper and more abrupt; and the striæ are more sharply curved backward on the dorsum. All the |