from the outer margin of the aperture to the opposite side of the volution, is more than three inches; the longitudinal diameter of the aperture is nearly two inches; the width a little less. Formation and localities. In the Upper Helderberg limestone, at Darien, N. Y. I have also seen the same from Port Colborne, Canada West. PLATYOSTOMA CONRAD. PLATYOSTOMA LINEATA. PLATE X, FIGS. 1-21. Platyostoma lineata, CONRAD. Jour. Acad. Nat. Sci. Phil., vol. 8, p. 276, pl. 17, f. 7. 1842. 66 66 66 SHELL subovate, approaching to subglobose. Spire elevated above the bodywhorl, though varying in degree; in some extreme varieties, on the same plane or below the outer volutions. The shell with four or five volutions when entire, but seldom preserving more than three,-the apex being usually imperfect. The outer volution usually very ventricose and regularly convex, a little depressed below the suture-line (but not canaliculate). Aperture suborbicular in perfect specimens, sometimes subrhomboidal; outer lip thin, with a sharp entire margin; columellar lip thickened, folded, and reflexed over the umbilicus, which in adult specimens, is entirely closed. SURFACE marked by fine, nearly equidistant, thread-like revolving striæ, which are cancellated by fine concentric striæ of about the same strength, but unequally distant; the latter sometimes bent abruptly backwards upon the back of the shell, indicating a sinus in the lip at some period of growth, and are frequently crowded in fascicles giving a rugose character to the surface. In well-preserved specimens, the surface is beautifully cancellated; and in worn and partially exfoliated specimens, some remains of these surface markings are usually visible, the revolving striæ being first obliterated. This species approaches in surface characters the P. turbinata of the Schoharie grit and Helderberg limestone; but the volutions are never so depressed on the upper side, and the aperture never so straight above, nor so extended on the lower side. It has usually a length of from one to two inches; young individuals of half an inch in length are not uncommon. A well formed individual measures one inch and a half long, with a vertical height of about one inch; another specimen, preserving its proportions free from compression, has a length of two inches, with a vertical height from base of aperture to apex of less than one inch and a half. A single extravagant specimen has a length of three inches, with a width of aperture of nearly two inches; the bodyvolution, for a distance of two inches from the aperture, is more than usually straight, and marked by crowded and unequal concentric striæ, without revolving striæ, while the latter are preserved on the upper part of the shell. A cast of a specimen in the Corniferous limestone of Western New York, bearing no evidence of compression, has a length of more than three inches, while the vertical diameter of the aperture does not exceed one inch and a half. The specimens which I have seen from Ohio and the West, are casts in limestone, which, not preserving their striæ, are identified only by their form and proportions. The original description of Platyostoma lineata is as follows: "Transversely subovate, with wrinkled reticulated striæ; aperture orbicular; spire depressed, or slightly elevated above the top of the body-whorl." Although no geological position is assigned to the species by Mr. CONRAD, and the figure given by him does not correspond with the prevailing form of the specimens examined, I am still inclined to regard it as the common form of the Hamilton group, of which I have seen several hundred individuals. Formations and localities. In the Upper Helderberg limestone throughout the limestone range from east to west in New York, and in the Hamilton group in the western part of the State. PLATYOSTOMA LINEATA var. CALLOSA. PLATE X, FIGS. 22, 23. Platyostoma lineata var. callosa, HALL. Illustrations of Devonian Fossils: Gasteropoda, pl. 9. 1876. This variety has the general form of specimens of P. lineata, except that the spire is extremely depressed, being almost flat upon the top. The mouth is suborbicular, with the peristome slightly sinuate on the upper side near its junction with the preceding volution. The inner lip is marked by a thickened callus, not observed in any other specimens, the callosity extending into the lip below (as shown in fig. 22), which thence assumes the ordinary features of the species. This variety is from the Hamilton group, near Geneseo, N. Y. PLATYOSTOMA LINEATA var. AMPLA. PLATE X, FIGS. 25, 26. Platyostoma lineata var. ampla, HALL. Illustrations of Devonian Fossils: Gasteropoda, pl. 9. 1876. The specimen has had about four and a half volutions, the last one enlarging very rapidly, and terminating in a broadly expanded aperture, as shown in fig. 26. The margin of the peristome is slightly sinuate on the upper side, and the columellar lip slightly grooved. The surface is marked as in other forms of this species. This form corresponds very nearly with the outline figure of the species P. lineata, given by Mr. CONRAD, loc. cit. It is of rare occurrence, so far as my own observations have gone, there being not more than five or six specimens among a collection of several hundred of the ordinary forms from different localities. There are, however, so many intermediate phases as to leave no doubt of the relations of the most extreme varieties represented in this and the preceding as well as the following form, which, if separated from their associates, might be considered distinct species. Those indicated as P. defigurata and P. euomphaloides may, perhaps, prove to be only varieties of the same species when a larger collection of specimens shall be examined—those at hand, at the present time, not furnishing the requisite data for uniting them with P. lineata. The specimen figured was found in the Hamilton shales, at Bellona, N. Y. PLATYOSTOMA LINEATA var. SINUOSA. PLATE XI, FIGS. 4-8. Platyostoma lineata v. sinuosa, HALL. Illustrations of Devonian Fossils: Gasteropoda, pl. 11. 1876. Several specimens of this species have been observed where the peristome at the base of the pillar lip is deeply indented by a sinus, as shown in the figures. One of the specimens figured has the spire slightly concave, the outer volution flattened upon the upper side, and symmetrically rounded below. The other specimen has more nearly the prevailing form, with moderately elevated spire, the volutions rounded above an orbicular aperture with deep sinus. This species, in its prevailing form, is very widely distributed within the limits of the State. Occurring in moderate numbers in the Upper Helderberg limestone from the Helderberg mountains, to Black Rock, it becomes abundant in the Hamilton group throughout the central and western part of the State. In the arenaceous shales of this group in Eastern New York, it is not a common form, but with the accession of calcareous matter in the deposit, it increases in numbers, and is one of the most common forms in localities along Seneca, Cayuga and Canandaigua lakes; at West Bloomfield in Ontario county, at Geneseo, Moscow and York in Livingston county, at Darien in Genesee county, and at Hamburgh on the shore of Lake Erie. PLATYOSTOMA DEFIGURATA. PLATE X, FIG. 24. Platyostoma defigurata, HALL. Illustrations of Devonian Fossils: Gasteropoda, pl. 9. 1876. The shell preserves five volutions which are rounded, gradually enlarging from the apex; the suture close. The surface is marked by fine concentric striæ, which become crowded and fasciculate on the outer volution-the revolving striæ being very subordinate. This shell differs from characteristic examples of P. lineata only in the more elevated spire, and in preserving one more volution than in ordinary forms of that species. It occurs in the Hamilton group, at Canandaigua lake, N. Y. PLATYOSTOMA EUOMPHALOIDES. PLATE X, FIGS. 27-29. Platyostoma euomphaloides, HALL. Illustrations of Devonian Fossils: Gasteropoda, pl. 9. 1876. SHELL depressed subhemispheric; spire moderately elevated; volutions three or four, gradually enlarging from the apex, the last one expanded, not ventricose, with its exterior or periphery flat or slightly convex, and flattened or gently concave in the middle above; suture-line close. Aperture Aperture expanded, broadly subovoid; the inner lip has a thickened callus, which projects in a prominent rim along the posterior border of the aperture. SURFACE marked by fine concentric striæ, which are crowded in fascicles. At present, we know only a single specimen having the character described. The flattened upper side of the volutions and the flattened periphery are very unlike any form of PLATYOSTOMA described, but at the same time it is not difficult to see how a still farther degree of variation in P. lineata var. callosa may result in such a form as this. In that variety, the summit is depressed, but the volutions are rotund and rapidly expanding, with an aperture suborbicular. Unlike the prevailing or characteristic forms of P. lineata, that one has a thickened callosity on the inner lip, but less defined and developed than in the specimen described as P. euompholoides. PLATYOSTOMA STROPHIUS. Platyostoma Strophius, HALL. Descriptions of New Species of Fossils, etc., p. 13. 1861. 66 66 SHELL obliquely ovoid. Apex minute; spire ascending, composed of about three or four volutions, very gradually expanding above; the bodywhorl ventricose, somewhat depressed-convex on the side, and sloping downward rather than swelling out in a rotund form; the upper volutions standing out prominently above the last one. Suture-line narrow, even, |