BIVALVKS CHAMA. 47 



from one inch to near a foot lon^. But this dimension 

 appears nothing when compared to the monstrosity of the 

 Chama gigas or giant clam, which, from a quarter of 

 an inch, will advance to the enormous size of four and a 

 half feet in breadth ; and two valves frequently weigh 

 between five and six hundred pounds. 



Of this species there are many varieties, they arc mostly, 

 however, more or less ribbed and foliated, sometimes im- 

 bricate or scaly ; the usual color of the commoner sorts is a 

 dirty white, but the rarest avc those which have a fine red- 

 pink, or yellow tinge. Some of them, when perfect, are 

 highly prized. The cartilage of the hinge has a dull 

 brown color, but when polished and cut in ovoid, its 

 iridescence is so brilliant that it rivals the opal in beauty, 

 and has even been sold for it. 



A grand mark of distinction in this genus is, that the 

 posterior slope is usually open or gaping, not unfrequently 

 having its margin crenulate. The valves are mostly ine- 

 quilateral, one protruding beyond the other, and often 

 appearing as if deformed. The hinge has usually a cal- 

 lous gibbosity, inserted in an oblique hollow. 



The anterior slope is usually closed. There is one spe- 

 cies of the Chama, the concamerata, which is in itself a 

 curiosity ; for, in the interior of each valve, there is placed 

 an additional one of smaller dimensions, which gives the 

 shell an appearance of being double. 



The more beautiful species of this genus are those 

 which are richly fohated or spined, — as the Chama laza- 

 rus, gryphoides, and arcineila; the varieties of vvhich 

 are sometimes highly worthy of admiration. 



It seems a principle with the Chamse, (like the spon- 

 dyli), to affix themselves to any extraneous substance ac- 

 cident throws in tlieir way. They often adhere to rocks. 



