OF THE UNITED STATES. 313 



MYA, Lam. 

 Species. 



1. M. *acuta. Shell oblong-subovate, narrowed 

 behind, rather strongly wrinkled ; posterior hinge 

 margin and posterior hasal margin subequally ar- 

 quated ; tip of the posterior margin equidistant from 

 the apex and middle of the base ; tooth moderate, 

 with a small, not prominent, tooth on its posterior 

 side. 



Length one inch and a half. 



Breadth two inches and four-fifths. 



Inhabits the southern coast. 



Cabinet of the Academy and Philadelphia Mu- 

 seum. 



I have but two valves, which are old and bleached. 

 It resembles M. arenaria, but is much smaller at the 

 posterior termination than the corresponding part of 

 that shell, as figured by Bruguiere. One of the valves 

 alluded to, is more than four inches in breadth ; it 

 corresponds very well in the outline with Pennant's 

 fig. of Arenaria. My decorticated specimens have 

 an obsoletely radiated appearance. 



2. M. *mercenaria. Shell subovate, convex, some- 

 what unequal, transversely wrinkled ; posterior hinge 

 margin curving abruptly downward to the tip of the 

 posterior margin, which is much nearer to the mid- 

 dle of the base than to the apex ; tooth robust, promi- 



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