26 GENERA OF SHELLS. 



CONCHA MARINE. 



Mostly no lateral teeth ; shell sometimes covered with an epi- 

 dermis, except at the leaks. 



CYPRINA. Shell equivalve, inequilateral, 

 obliquely cordate ; beaks obliquely curved. 

 Hinge with three unequal teeth, approximated 

 at base, subdivaricate superiorly ; a lateral 

 tooth, distant from the hinge, on the anterior 

 side, sometimes obsolete ; nymphaeal callosi- 

 ties large, arcuated, terminated near the beaks 

 by a pit ; ligament exterior, partly under the 

 beaks. 



The cyprinse are in general rather large shells, very 

 like the veneres, and chiefly distinguished by having 

 a compressed lateral tooth on the anterior side ; by 

 their large nymphre, generally terminated by an oval 

 pit, sometimes singularly large near the beaks ; by the 

 ligament extending under the beaks, and there filling 

 up the terminal pit of the nymphse, and by having an 

 epidermis. 



C. gigas, Islandica,Pedomontana, tenui-stria. 



CYTHEREA. Shell equivalve, inequilateral, 

 suborbicular, triangular or transverse. Hinge 

 of the right valve four toothed, three of which 

 are divergent and approximate at base, the 

 other solitary, under the lunule. The other 

 valve with three diverging teeth, approximate 

 at base, with a remotish pit, parallel to the 

 margin ; lateral teeth none. 



