94 



[ Senate 



Merista LiEvis ( Yanuxem). 



Pal. N.Y. Vol. iii, pi. 39, f. 3. 



Shkll ovate, thin, somewhat ventricose : ventral valve the larger, 

 most gibbous in the centre and umbonial region, having a small 

 mesial sinus extending from the front more than half way to the 

 umbo ; beak prominent, ventricose, incurved, not perforate : 

 dorsal valve regularly convex, rounded in the middle, but 

 without a defined mesial fold ; beak incurved. Surface smooth, 

 or only marked by obscure concentric lines and occasional 

 stronger concentric wrinkles of growth. 



Some varieties of this species, especially the adult shell, often resemble 

 Merista hella, but differ in being proportionally longer, and are never 

 marked by a sinus on the dorsal valve. Young shells are sometimes com- 

 paratively much more compressed, and often destitute of any trace of a 

 sinus on either valve. 



Geological position and locality. Shaly and compact limestones of the 

 Lower Helderbcrg group : Albany, Schoharie and Herkimer counties. 



6 



]lfS3X3TA LJiVIS. 



