GASTEROPODA. 

 GENUS PLATYCERAS (Conrad). 



PLATYCERAS (ORTHONYCHIA) DENTALIUM ( n. s.). 



Shell slender, elongate, subspiral, making about half of one volution 

 in the length of one and a half inches, somewhat flattened ob- 

 liquely from the base to near the apex : section subelliptical, 

 giving the diameters about as two to three. The middle of the 

 flattened sides are often a little concave, rounded towards the 

 apex, which is minute and abruptly incurved. 



Surface marked by transverse or concentric striae of growth, and 

 by longitudinal sulci which are conspicuous on the lower part of 

 the shell, and give to the transverse strise a strongly undulated 

 character. Aperture oblique. 



In a specimen one inch and a half in length, the greatest diameter 

 is less than half an inch. 



This species is much more slender and less distinctly spiral than the P 

 toHuosus of the Oriskany sandstone, and differs in the same features mora 

 extremely from any of the species known in the Lower Helderberg group. 



Geological formation and locality. In the limestone of the Upper 

 Helderberg group : near AVilliamsville and Buifalo, N.Y. 



-^ PLATYCERAS (ORTHONYCHIA) SUBRECTUM. 



OaTHONrcniA (genus proposed) : Report Fourth District New- York Geological 



Survey, pag. 172, no. 68, f. 3. 



PLATYCERAS SUBRECTUM . Twclftli Annual Report of the Regents on the State 



Cabinet, p. 18. 



Shell nnguiform, elongate, subspiral, making not more than a 

 quarter of a volution in the length of three-fourths of an inch, 

 below which it is entirely straight. Apex minute, abruptly in- 

 curved, solid, nearly cylindrical for a short distance below the 

 apex and gradually compressed, becoming a little concave on the 

 posterior side : aperture somewhat oblique. 



Surface marked by concentric striae, which are sometimes crowded 

 together, forming ridges or wrinkles. 



This species is more robust and rapidly expanding than the P. dentalium^ 

 and is more enrolled at the apex ; but it does not show the longitudinal 

 sulci and ridges which are characteristic of P. dentalium. 

 ALBA.NY, N.Y.] ^ r^ f; [ August 1861, 



