398 PALAEONTOLOGY OF NEW-YORK. 



This species is readily distinguished by its depressed form and nearly central 

 apex, consisting, when entire, of a single minute volution. The pustulose markings 

 seem to be characteristic of the siiecies. 



Fig. 3 a. The upper side of a speuiiueu in wliich the apex is partially broken off. [ The 

 luiuuto volution is seen on the specimen, though not represented in the figure.] 



Fig. 3 6. Profile view of a young specimen. 



Geological position and locality. In the central part of the Lower Helderberg 

 group : Schoharie county. 



Platjceras perlatuiii ( n. s.). 



Plats LXI. Fia. 4 a, h. 



Shell extremely depressed-subhemispherical, with the apex subcentral 

 and obtusely pointed, very gradually sloping to the margin : aperture 

 nearly circular, somewhat broader posteriorly ; peristome scarcely 

 sinuate. 



ScKFACE marked by fine undulating striae. 



This species is more depressed than the preceding; and from the appearance of 

 the surface, which preserves but a small portion of the shell, it has never been 

 marked by plications. The cast on the anterior side is contracted in a broad con- 

 centric groove, but it presents no marks of muscular impressions. 



Fig. 4 a. View looking upon the summit of the fossil. The indentation near the summit may 

 have been due to the involution of tlie apex of the shell, which afterwards became 

 solid, as the apex of the cast is not broken. 



Fig. 4 6. An oblique postero-lateral view of the specimen. 



Geological positioti and locality. In the central part of the Lower Helderberg 



group : Schoharie county. 



Platjceras calantica ( n. s.). 



Plate LXII. Fio. 1, 2, 3, 4, 5. 



Shell obliquely or arcuately subconical : apex con.sisting of one and a 

 half to two minute volutions, from which the body of the shell expands 

 very abruptly, becoming extremely ventricose below and broadly cam- 

 panulate at the aperture ; peristome scarcely .'inuous. 



