OF THE UNITED STATES. 811 



the hinge slope ; hinge slope with a rectilinear profile, 

 and flattened, oblong-subcordate surface ; valves un- 

 equally wrinkled; posterior margin rounded, short, 

 with a reflected edge, and subniarginal carinated line ; 

 within undulated, anterior margin glabrous, and with 

 an indented submarginal line corresponding with the 

 exterior carinated one. 



Length one inch and nine-tenths. 



Width two inches and seven-tenths. 



Thickness one inch and one-tweutieth. 



Inhabits the coasts of Georgia and East Florida. 



Cabinet of the Academy and Philadelphia Mu- 

 seum. 



Not uncommon on the southern coast, and may be 

 readily distinguished by the carinated line on the 

 posterior sub margin. 



2. L. *canaliculata. Shell transversely oval- or- 

 bicular, very thin and fragile, white, inflated ; valves 

 equally, concentrically, and regularly grooved, with 

 very feint parallel lines within the grooves ; posterior 

 margin short, subcuneiform, compressed; a marginal, 

 longitudinal, irregular, subimpressed line, between 

 which and the edge, the grooves become mere 

 wrinkles ; posterior slope subrectilinear, hiatus con- 

 siderable ; anterijr margin regularly curved, the 

 slope convex ; within grooved as without, anterior 

 angle glabrous. 



Greatest length two inches and one-twentieth. 



Breadth two inches and a half. 



Thickness one inch and one-fourth. 



