LAMELLIBRANCHIATA FEOM BASE OF UPPER MARLS. 221 



the posterior cardinal slope is concave. Surface of the cast marked by 

 a few undulations of growth. Muscular impressions small and faintly 

 marked. 



This species might readily be mistaken for a cast of Periplomya elliptica 

 Gabb, from the Lower Marls, as it very closely resembles it, but on close 

 compai'ison it is seen to be wider posteriorly, and not so pointed at tlie ex- 

 tremity ; the anterior end is proportionally less, and the beaks situated 

 nearer the middle of the length, while the valves are more ventricose, 

 especially in the vicinity of the beaks. 



Formation and locality. — In the dark-colored marls at the base of the 

 Upper Marls, near New Egypt, New Jerse}\ Collection at Eutger.s College. 



