52 CONCHOLOGY. 



Cyclas and the Venus, and contains but one living species ; 

 Lamarck makes two, though at first he characterized eight. 

 Cyprina tennistria. Cyprina Islandica. 



C. Islandica. The Icelandic Cyprina. PL 9, fig. 2. 



Shell thick, regular, heart-shaped, covered with dark 

 brown epidermis ; white interior ; sub-striated longitudi- 

 nally ; apices very strongly recurved anteriorly, and often 

 contiguous ; hinge thick, sub-similar, formed by three cardi- 

 nal teeth but little convergent, and by one remote posterior 

 lateral tooth, sometimes obsolete ; ligament very thick, con- 

 vex, fixed to large, arched, nymphal callosities, preceded 

 by a cavity more or less deep, hollowed immediately behind 

 the summits ; muscular impressions sub-circular and very 

 distant. 



5. Cytherea. Seventy-eight species. 



This genus was taken from the Venus, and is easily defined 

 as distinct from it by having four primary teeth on one valve, 

 and only three united on the other, with an isolated cavity, 

 oval and parallel to the margin ; the lateral teeth divergent 

 to the summit. In some species the internal margin is en- 

 tire, having the anterior cardinal tooth with a striated canal 

 or uneven sides ; in others the anterior cardinal tooth is en- 

 tire, without a striated canal ; sometimes the internal margin 

 is crenulated or dentated. 



Shell solid, regular, equivalve, inequilateral ; apices equal, 

 recurved, and slightly projecting ; four primary teeth on one 

 valve, of which three are divergent and approximating at the 

 base, and one remote ; three primary divergent teeth on the 

 other valve, with a distant cavity parallel to the edge. 



Cytherea lusoria. Cytherea graphica. 



C. petechialis. C. morphina. 



C. impudica. C. purpurata. 



C. castanea. C. casta. 



C. zonaria. C. corbicula. 



