CONCHOLOG-V. 67 



C. Lazarus. C. Japonica. 



C. gryphoides. C limbula. 



C. unicornis. C. asperella. 



C. radians. C. albida. 



C. croceata. 



3. Genus Etheria. 

 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 anterior, with a marginal palleal im pression 

 Inhabits the Indian Ocean. Five species. 



Etheria elliptica. Etheria semJlunata. 



E. trigonula. E. transversa. 



E. carteronii, 



FAMILY XV. 



Tridacnea. Two genera. 



I. Genus Tridacna. 

 .Animal. Body somewhat thick; edges inflated, lobes of the 

 mantle adhering, and united in nearly all their circumference, so 

 as to present but three apertures, the first inferior and anterior, for 

 the egress of the foot, the second superior and posterior for the 

 branchial cavity, the third much smaller and in the middle of the 

 dorsal edge ; two pairs of labial appendages, thin, nearly filiform, 

 in the middle of which is a very small buccal orifice ; branchiae 

 long and narrow ; abdominal muscular mass considerable, and 

 giving issue, as if from a cup, to a thick bundle of byssoid muscu- 

 lar fibres. 



Shell. Thick, solid, of variable size, regular triangular, inequi- 

 lateral ; summits inclined posteriorly, hinge dissimilar, entirely 

 anterior to the summit ; a lamellous precardinal tooth and two 



