26 
PALAEONTOLOGY OF NEW YORK. 
and sometimes appearing as very narrowly and deeply canaliculate. Aper¬ 
ture ovate, and, in one specimen, with a sinus near the base. 
Surface marked by fine concentric striae, which are sometimes crowded into 
wave-like fascicles or undulating folds, and sometimes abruptly bent for¬ 
ward near the base. Occasionally these striae 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 XX, FIG. 9. 
Platyostoma aplata, Hall. Illustrations of Devonian Fossils: Gasteropoda, pi. 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. 
PLATE IX, FIGS. 25, 28. 
Pleurotomaria unisulcata [?] Conrad. Jour. Acad. Nat. Sci. Phil., vol. 8, pt. 2, p. 271, pi. 17, fig. 9. 1842. 
Platyostoma unisulcata (Conu.) Hall. Illustrations of Devonian Fossils: Gasteropoda, pi. 10. 1876. 
The description given by Mr. Conrad is as follows: 
“ Short-fusiform; spire conical-depressed ; upper surface of the large volu¬ 
tion 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 rec¬ 
tilinear towards the labrum, slightly convex above the aperture.” 
