CONTRIBUTIONS TO TAL/EONTOLOGY. 33 



PLATYCERAS CARTNATUM ( n. s.). 



Shell obliquely subconical or subpyramidal; the nucleus or apex 

 minute, and making from one to one and a half volutions Vvliich 

 are vertically compressed, and below which the body-volution is 

 abruptly expanded ; the dorsum angular, or marked by an angu- 

 lar carina which often becomes double in old shells, or is rounded 

 on the summit. This angularity or carina indicates the existence 

 of a notch or sinus in the peristome; and sometimes there may 

 have been two such sinuosities close together, giving the double 

 carina. There is usually a depression along one or both sides of 

 the carina, with longitudinal folds on one or both sides, which 

 become more strongly developed towards the aperture, and are 

 very conspicuous in old shells : the right side is more expanded 

 than the left, and in some well-preserved specimens is nearly 

 twice as wide. Aperture very oblique and subtriangular, and the 

 peristome sinuous. 



Surface marked by fine closely arranged undulating striae of growth, 

 which are not lamellose. 



This species is very well marked in its dorsal carina and rapidly expanding 

 body-volution, which spreads always more on the right side. The surface, 

 though striated, is close, and the shell compact ; differing in this respect 

 from most of the other species. Having examined more than a dozen in- 

 dividuals, from the length of less than half an inch to that of an inch and 

 a half, the characters mentioned are preserved in a marked degree in all of 

 them. In the largest specimens, the aperture is a little more than an inch in 

 its greatest diameter, and nearly equal to the height of the shell. 



Geological formation and locality. In limestones of the Upper Helder- 

 berg group: Helderberg mountains and Williamsville, N.Y., and Sandusky, 

 Ohio ; in the Hamilton group, at Eighteen-mile creek, Darien, Pavilion, 

 Canandaigua and Seneca lakes. 



PLATYCERAS BUCCULENTUM ( n. s.). 



Shell ventricose, obliquely subovoid : apex extremely attenuate, 

 making one to two closely enrolled volutions, with a gently 

 expanding diameter, and below this more abruptly expanding 

 and becoming very ventricose in the middle and below, spreading 



1861.] 5 [Senate No. 116.] 



