CONCHOLOGY. 71 



nated at its extremity by a part much narrower than the base ; 

 superior lobes of the branchiae very short. 



Shell. Irregular, adhering, inequivalve, inequilateral ; summits 

 more or less twisted spirally, especially in the lower valve by 

 which these animals have the foculty of affixing themselves to 

 other bodies; hinge dissimilar, thick, formed by a single 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 damaecornis. Charaa aeruginosa. 



0. crenulata. C. decussata. 



C. arcinella. C. ruderalis. ' 



C cristella. C. Japonica. 



C. Lazarus. ' C limbula. 



Vj. gryphoides. O. asperella. 



C unicornis. C. albida. 



C radians. C. croceata. 



C. exogyra.* C. Florida.* 



3. Genus Eiheria. PI. VITI. 



Animal. Unknown. 



Shell. Adhering, irregular, thick, much nacrcd, 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 anterior, with a marginal palleal impression. 

 Inhabits the Indian Ocean. Five species. 



Etheria elliptica. Etheria semilunata. 



E. trigonula. E. transversa. 



E. Carteronii. 



