CONCHOLOGY. 71 
nated at its extremity by a part much narrower than the base ; 
superior lobes of the branchie very short. 
Shell. Irregular, adhering, inequivalve, inequilateral ; summits 
more or less twisted spirally, especially in the lower valve by 
which these animals have the faculty of affixing themselves to 
other bodies ; hinge dissimilar, thick, formed by asingle lamellous 
tooth arcuated, subcrenulated, postcardinal and articulated in a 
furrow of the same form ; ligament anterior and postapicial ; two 
large muscular impressions, distant. British and American seas. 
Eighteen living species. 
Chama damecornis. Chama eruginosa. 
C. crenulata. C. decussata. 
C. arcinella. C. ruderalis. 
C. cristella. C. Japonica. 
C. Lazarus. C. limbula. 
C. gryphoides. C. asperella. 
C. unicornis. C. albida. 
C. radians. C. croceata. 
—_ 
C. exogyra.* C. Florida.* 
3. Genus Etheria. Pl. VIII. 
Animal. Unknown. 
Shell. Adhering, irregular, thick, much nacred, inequilateral, 
inequivalve ; summits subcephalic, thick, indistinct, in a species 
of heel, growing longer with age; hinge without teeth, callous, 
irregular and thick ; ligament subdorsal in the exterior portion of 
the shell, and prolonged to a point internally ; two irregular 
oblong muscular impressions, one superior and subposterior, the 
other inferior and anterier, with a marginal palleal impression. 
Inhabits the Indian Ocean. Five species. 
Etheria elliptica. Etheria semilunata. 
E. trigonula. E. transversa. 
E. Carteronii. 
