LOWER HELDERBERG ROCKS. 337 



Platyceras bisulcatuiii ( n. s.). 



Plate LX. Fio. 6 d, e. 



Shell obliquely and very depressed-subconical : apex consisting of one 

 or two smaU volutions, \> hich are free from plications and slightly 

 ob ique; last volution free, abruptly expanding and becoming ventri- 

 cose towards the aperture : aperture round ; peristome sinuate, some- 

 what reflexed. 



Surface, on the upper or right side of the body- volution, markeci by two 

 strong longitudinal furrows, which divide that side of the shell into 

 three broad lobes or plications, the opposite side being obscurely p.'icate ; 

 transversely marked by lamellose striae, which are abruptly undulated 

 on the depressions and elevations of the surface, and obscurely marked 

 by fine longitudinal striae. 



The first volution is broken off in the specimen figured, and the aperture a little 



distorted by pressure. 



Fig. 6 d. View of the upper side of the spire, showing the two sharp grooves and the broad 

 lobes. 



Fig. 6 e. The left side, showing the sinuous striae with an undefined longitudinal plication : 

 there are, besides this, one or two obscure plications. 



Geological position and locality. In the shaly limestone of the Lower Helderberg 

 group : Schoharie county. 



Platyceras pileifomie ( n. ».). 



Plate LXL Fia. 3 a, b. 



Shell very depressed-conical or hemispheric : apex subcentral, consisting 

 of a single minute volution, from which the surface slopes almost 

 equally on all sides to the margin : aperture nearly round ; peristome 

 sinuous. 



Surface longitudinally plicated ; plications broader below, and scarcely 

 reaching to the apex : a few pustulose markings on the sides and near 

 the apex ; concentrically striated by fine closely arranged striae. 



