54 CONCHOLOGY. 



mantle closed behind, and pierced by two oval apertures with 

 cirrous edges : no veritable tubes. 



Shell. With epidermis ; thick, regular, substriated longitudi- 

 nally, subcordiform, equivalved, inequilateral ; summits strongly 

 flexed to the front and often contiguous ; hinge thick, subsimilar, 

 formed by three slightly converging qardinal teeth, and by a'pos- 

 terior lateral tooth, sometimes obsolete ; ligament very thick ; mus- 

 cular impressions distant, subcircular, and united by a narrow 

 marginal band. Inhabits the Atlantic Ocean and British seas.' 

 Two living species. Seven fossil. 



Cyprina tennistria. Cyprina Icelandica. 



2. Genus Cytherea. PI. VII. 



Animal. Oval or round, generally but little compressed ; edges 

 of the mantle undulous, and garnished with tentacular cirri iu 

 one row; foot considerable, compressed, trenchant, in other re- 

 spects div ersiform ; tubes tolerably elongated, and most usually 

 united ; mouth small ; labial appendages quite small ; branchias 

 wide, short, free, or not united either with one another or with 

 those of the opposite side. 



Shell. Solid, equivalve, regular, inequilateral ; summits equal, 

 reflexed, and slightly projecting ; four primary teeth on one valve, 

 of which three arc divergent, and approximating at the base, and 

 one remote — this circumstance easily distinguishing it from the 

 Venus. On the other valve are three primary divergent teeth 

 with a distant cavity parallel with the edge. Inhabits the British, 

 Mediterranean, and American seas. Eighty-three living species. 

 Nine fossil. 



Cytherea petechialis. Cytherea tigrina. 



C. morphina. C. pulicaris. 



C. Castanea. C. numulina. 



C. casta. C abbreviata. 



C. lusoria. C. pectinata. 



C. graphica. C. flexuosa. 



C. impudica. C. ranella. 



C. purpurata. C. lunularis. 



C. zouaria. C. divaricata. 



