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 cardinal 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 in 
one row; foot considerable, compressed, trenchant, in other re- 
spects diversiform ; tubes tolerably elongated, and most usually 
united; mouth small; labial appendages quite small; branchie 
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 are 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. Iunularis. 
C. zonaria. C. divaricata. 
