26 PALEONTOLOGY 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 strije, which are sometimes crowded into 

 wave-like fascicles or undulating folds, and sometimes abruptly bent for- 

 ward near the base. Occasionally these stria) 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, 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, 20. 



PUurotomaria unigulcata[1] Coxkad. Jour. Acad. Nat. Sci. Phil., vol. 8, pt. 2, p. 271, pi. 17, fig. 9. 1842. 

 Platyottotna unigulcata (Conk.) 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, margin* the suture; 

 penultimate whorl rounded, obtusely carinated at the suture; base nearly rec- 

 tilinear towards the labrum, slightly convex above the aperture." 



