and sometimes appearing as very narrowly and deeply canaliculate. Aperture ovate, and, in one specimen, with a sinus near the base. SURFACE marked by fine concentric striæ, which are sometimes crowded into wave-like fascicles or undulating folds, and sometimes abruptly bent forward near the base. Occasionally these striæ are very regular and even, as in STROPHOSTYLUS. This species is less ventricose than the P. lineata, and the spire much more elevated, while no revolving lines have been observed. In many respects it resembles STROPHOSTYLUS; but the aperture has not been entirely determined. Formation. In the Corniferous limestone. PLATYOSTOMA APLATA. PLATE XI, FIG. 9. Platyostoma aplata, HALL. Illustrations of Devonian Fossils: Gasteropoda, pl. 11. 1876. The specimen is a part of a large individual, retaining between three and four volutions, which are flattened upon the upper side,-the flattening partly due to pressure. The form of aperture is unknown, and no definite surface markings are preserved. Formation and locality. In the Schoharie grit, Schoharie, N. Y. PLATYOSTOMA UNISULCATA. Pleurotomaria unisulcata [?] CONRAD. PLATE IX, FIGS. 25, 26. Jour. Acad. Nat. Sci. Phil., vol. 8, pt. 2, p. 271, pl. 17, fig. 9. 1842. The description given by Mr. CONRAD is as follows: "Short-fusiform; spire conical-depressed; upper surface of the large volution slightly concave from the outer margin to a carinated line which borders a transversely rugose sulcus; another, but more obtuse line, margins the suture; penultimate whorl rounded, obtusely carinated at the suture; base nearly rectilinear towards the labrum, slightly convex above the aperture." "Locality. Near Schoharie, in Onondaga limestone." A specimen, which has been supposed to represent the original of Mr. CONRAD, is illustrated in figs. 25 and 26, plate 9. The apparent band bordering the suture is caused by a narrow depression of the surface, parallel with the suture, from which the striæ rise abruptly and bend forward, leaving a narrow depressed line or canaliculation along the suture. It has not the defined band of PLEUROTOMARIA, and the recurving of the striæ is less distinct and abrupt than in some other specimens of PLATYOSTOMA. Formation and locality. In limestone of the Upper Helderberg group, Schoharie, N. Y. PLATYOSTOMA UNISULCATA var. PLATE XI, FIGS. 1-3. Platyostoma unisulcata var., HALL. Illustrations of Devonian Fossils: Gasteropoda, pl. 11. 1876. This form, from the Hamilton group at West Bloomfield, N. Y., has so much the form and aspect of Mr. CONRAD's original figure ut cit., except in the lesser elevation of the spire above the last volution, and the absence of a sutural band, that I have placed it under the above designation. PLATYOSTOMA TURBINATA. PLATE IX, FIGS. 12-24. Platyostoma turbinata, HALL. Fourteenth Rep. N. Y. State Cab. Nat. Hist., p. 106. 1861. 66 66 66 SHELL Subturbinate, sometimes approaching a subglobose form. Spire depressed, or more or less elevated above the outer volution, sometimes nearly on the same plane; volutions three or four, rapidly expanding, the last extremely ventricose, with the lower part projected in the direction of the columella, which is much extended. Aperture subovate, broader above, narrowing and often extended below. SURFACE marked by fine subequal concentric striæ, crossed by finer revolving striæ; the former variously undulated upon the surface, indicating sinuosities in the aperture at different stages of growth. In older shells the striæ become lamellose and often crowded in fascicles. In well-marked specimens of the species, as originally described, the spire rises little above the general plane of the volutions, as shown in figs. 12, 14, 15, 16 and 19. Figs. 20 and 24 show a more elevated spire. Figs. 23 and 24 represent an extremely old shell, much thickened, and showing very irregular growth; the striæ are crowded in strong fascicles, and curved backward on the summit of the last volution, upon the periphery, and again below the periphery. Formation and localities. In shaly limestone of the Upper Helderberg group, in the town of Onondaga, Onondaga county, and more rarely in the Helderberg mountains, Albany and Schoharie counties. Some varieties of the species also occur in the Hamilton group, at York and at West Bloomfield, N. Y. PLATYOSTOMA TURBINATA var. COCHLEATA. PLATE IX, FIGS. 1-11. Platyostoma turbinata var. cochleata, HALL. Illustrations of Devonian Fossils: Gasteropoda, pl. 10. 1876. SHELL turbinate. Spire elevated, conical; volutions about four or five; periphery of the last volution obtusely rounded or distinctly subangular, with a sinus in the margin of the aperture; the last volution sometimes becoming free near the aperture, as shown in figs. 5, 6 and 7. Aperture obliquely subovate or ovate; peristome sinuous, often with a deep notch in the upper margin, and sometimes continued in a columellar extension below. The specimens referred to this variety all agree in having an elevated spire, with rounded volutions above the last one, which is almost invariably subangular. Specimens Specimens represented in figs. 8, 10 and 11 are symmetrical, and have distinctly marked characters; but it is not possible to restrict the variety to such forms, unless by indicating as distinct varieties several of the other forms illustrated. Formation and locality. In limestone of the Upper Helderberg group, in Onondaga, Onondaga county. Until the discovery of this locality by Prof. E. A. STRONG, few individuals of the type of P. turbinata were known, and these were very constant in their characters. All the varieties of form represented in the illustration of this species have been derived from that locality, which has afforded probably twenty times as many specimens of the species as all other localities in the State. Strophostylus varians is not known to me from any other locality; and Platyostoma lineata, and several species of Platyceras, are also common in the same place. It would appear that the physical conditions favoring the abundant production of individuals has, at the same time, favored a degree of variation unknown under conditions existing elsewhere. PLATYOSTOMA TURBINATA var. PLATE IX, FIGS. 27-30. Platyostoma turbinata var., HALL. Illustrations of Devonian Fossils: Gasteropoda, pl. 10. 1876. I have indicated in the Illustrations of Devonian Fossils, pl. 10, the forms above cited as a variety of P. turbinata, the principal features of which are the low turbinate form, depressed spire, aperture narrow and extended vertically, with a distinct sinus in the upper margin of the peristome.. In this variety the spire is more elevated than in typical forms of P. turbinata, but does not rise so high as in V. cochleata. Compared with the latter, the volutions are less rotund, obscurely angulated at the periphery, with a very similar form of aperture. The specimen (figs. 28-30) is from the Hamilton group in the neighborhood of Moscow, N. Y. Its surface, as shown in fig. 28, is incrusted by a Bryozoan. PLATYOSTOMA PLEUROTOMA. PLATE IX, FIGS. 31-35. Platyostoma pleurotoma, HALL. Illustrations of Devonian Fossils: Gasteropoda, pl. 10. 1876. SHELL rotund, subturbinate. Spire depressed; volutions rounded, gradually enlarging, and the last one much expanded. Aperture broadly oval, and extended below; peristome more or less sinuous, and, on the columellar side, extended below in a thickened and slightly contorted callosity. SURFACE finely striated with concentric and revolving striæ, the latter, conspicuous, and the former scarcely perceptible. In one specimen, a distinct narrow band marks the suture-line; and in another, a narrow carina marks the periphery, giving the aspect of PLEUROTOMARIA. Formation and locality. In limestone of the Upper Helderberg group, Onondaga, N. Y. STROPHOSTYLUS UNICUS. PLATE XI, FIGS. 14, 15. Strophostylus unica, HALL. Descriptions of New Species of Fossils, etc., p. 13. 1861. 66 66 66 66 66 unicus SHELL suborbicular; height and length about as three to four. Spire consisting of three or four volutions; the apex moderately elevated above the outer volution; suture close, and the volutions evenly convex upon the upper side; body-whorl ventricose, evenly and equally rounded upon the back. Aperture subovate, a little extended at the lower side, and slightly straightened on the posterior side; outer lip regularly curved; columellar lip thickened and slightly twisted, the fold being near the upper part of the lip. SURFACE marked by fine, crowded, concentric striæ, which are broadly curved backward on the dorsum; shell very thick. At one point, where the shell is broken away, the surface within the cavity is marked by revolving striæ. |