AXINiEIXiE. 5 11 



Species of Argina. 





Americana, Gray. Indica, Gruel. 



brevifrons, Sow. t pexata, Say. 



Genus LUNA RCA, Gray. 



Shell globose, sub-cordiforin, nearly equivalve ; surface 

 of valves radiately costate, and covered with a brown, folia- 

 ceous epidermis. Hinge with the hinder tooth elongate, 

 narrow in the middle ; the front tooth of the left valve 

 ovate, elevated, entire, fitting into a cavity in the inner 

 edge of the front margin of the right valve ; ligament ex- 

 ternal ; ligamental area narrow, smooth. Pallial im- 

 pression entire. 



Ex. L. costata, Gray, pi. 125, fig. 8, 8, a. 



This genus, of which only one species is known, from 

 America, is peculiar from the anterior hinge-tooth being 

 entire and without the usual divisions. 



Sub-fam. AXIN^EIN^E. 



Gills dependent. Foot securiform, simple, without any 

 byssal groove at the base. 



Shell orbicular, with the hinge-margin semicircular ; 

 cartilage in small marginal pits. 



Genus AXINJiA, Poli. 



Shell equivalve, equilateral, or nearly so, orbicular, 

 closed ; surface of valves smooth, or striated, or with radi- 

 ating furrows, invested with a fimbriated epidermis ; mar- 



VOL. II. 4 A 



