CONTKIBUTIONS TO PALEONTOLOGY. 81 



The specimen is imperfect at the apex, and the lower portion 

 makes less than half a turn from the aperture in the length of 

 about two inches : apex unknown. Anterior side of the body- 

 volution convex and ventricose : posterior side distinctly concave; 

 the right side moderately convex, and the left side rounded. 

 Surface marked by concentric undulating striae. 



The length of the fragment is two inches; the aperture, from the 

 posterior to the anterior side, is about seven-eighths of an inch, 

 and the transverse diameter a little more than one inch. 



This species resembles the P. tortuosum of the Oriskany sandstone, but 

 is more robust and more rapidly expanding towards the aperture, which is 

 much less oblique than in that species, while the concave posterior and 

 prominent anterior side are distinguishing features. 



Geological formation and locality. In the limestone of the Upper 

 Helderberg group : Williamsville, Erie county, N.Y. 



PLATYCERAS CONICUM ( n. s.). 



Shell erect, conical, the minute apex closely incurved? Body- 

 volution entirely straight, with broad undefined longitudinal 

 ridges and depressions, which become more distinct towards the 

 aperture : height of the shell a little greater than the width 

 of aperture, which is a little longer than wide. Surface marked 

 by concentric undulating striae which become sublamellose to- 

 wards the aperture, and are sometimes closely crowded and 

 wrinkled with numerous knots or nodes. Peristome deeply sinu- 

 ous ; the width from the anterior to the posterior side a little 

 greater than the transverse diameter. 

 The length of the shell is one and a half inches or more, with 



the aperture a little less. 



This species approaches the P. pyramidatum of the Lower Helderberg 

 group, but is less elongate, the peristome is more sinuous, and the indication 

 of longitudinal ridges and depressions is more distinct : the crowded 

 wrinkled and nodose striae are likewise a distinctive feature. 



Geological formation and locality. In the Hamilton group, Ontario 

 county ; and in the Upper Helderberg limestone at Darien and Williams- 

 ville, N.Y. 



1861.] 



