hippopus. 465 



front near the beak ; surface of valves with prominent, 

 scaly, radiating ribs ; margins strongly dentate. Hinge 

 composed of a single primary, compressed tooth in each 

 valve, two posterior lateral teeth in one valve, and a single 

 one in the other ; ligament external, marginal. 



Syn. Labrum, Meusch. Lavacrum, Hippopus, Mart. 

 Tridacna, Da Costa. 



Ex. C. scapha, Meuschen, pi. 113, fig. 2. Shell, C. 

 scapha, fig. 2, a, 2, b. 



The byssal orifice in the animal is large, close to the 

 umbo, occupying nearly the whole anterior side ; the byssus 

 is very large ; the foot is small, finger-like, and grooved ; 

 and the adductor muscle is round, large, and central. The 

 shell, according to Dr. Carpenter, is very dense, being so 

 calcified as almost to obliterate every trace of organic 

 structure. The species are found imbedded in coral-reefs 

 in the Pacific and Indian Oceans, and in the China Sea. 

 The shells often attain a large size, sometimes weighing 

 upwards of 500 lbs., and measuring two feet across. 



Sjiecies of Chametrachcca. 



elongata, Lam. scutrum, Meusch 



gigas, Linn. serrifera, Lam. 



mutica, Lam. squamosa, Lam. 

 scapha, Meusch. 



Genus HIPPOPUS, Meuschen. 



Shell equivalve, regular, trigonal; byssal sinus at the 

 fore-part of valves, indistinct ; surface of valves with imbri- 

 cated, scaly, radiating ribs. Hinge composed of two com- 

 pressed, unequal, primary teeth in each valve; ligament 

 external, marginal. 



