18 



[Assembly 



The following figures are illustratrations of two other species ; one of 

 them having a single minute close volution at the apex, and the other being 

 simply bent or arcuate. For the latter forms, I had proposed in 1843 the 

 generic name Oethontchia* ; but an examination of a great number of 

 specimens has not shown any reliable character, by which they may be sepa- 

 rated from Platycbsas. 



Platyceras bisulcatum. 



Plattcekas subrectum. 



In the farther removed from the spiral forms of this genus, we have the 

 straight and nearly straight species, which, in the striate, cancellate, and 

 plicate surfaces and sinuous peristomse, still preserve externally the generic 

 characteristics. 



Platyceras plicattjm. 





.^ 



Fig. 1. The anterior side of a specimen which is partially crushed. 

 Fig. 2. The left side of a specimen. 



* Report on the 4th District, Geology of New-York, 1843 



