OF THE UNITED STATES. 265 



3. M. *hamatas. Shell very much contracted 

 and incurved at the base, which is acute ; valves 

 striated on every part of the exterior with longitudi- 

 nal, elevated lines, which are bifid and sometimes 

 trifid towards the tip ; colour dark fuscous ; within 

 dark purpurescent, with a whitish margin. 



Length one and one-fifth of an inch. 



Breadth nearly four- fifths of an inch. 



Inhabits the Gulf of Mexico. 



Cabinet of the Academy and Philadelphia Mu- 

 seum. 



A common species in the Gulf of Mexico, and is 

 frequently carried to market at New Orleans, attach- 

 ed to the common oyster. It is remarkably distinct 

 from M. demissus by the great incurvature of the 

 beaks, by its inferiority in magnitude, aud by having 

 the striae extending over every part of the surface of 

 the shell. 



I cannot refer it to strialulus, with which it seems 

 to have some affinity, as that species is described to 

 be nearly diaphanous. It seems to have some af- 

 finity with the M. decussatus Lam. but is much 

 smaller, and the transverse striae are not very promi- 

 nent. 



MODIOLA, Lam. 



Species. 



1. M. Americana. Var. Shell oblong, hinge mar- 

 gin elevated in a right line, from the beak to the 



33 



