48 BIVALVES. CHAM A. 



uncommon size: tlie C. gigas, for instance, (or Giant clam), 

 is a specimen of the unusual magnitude to which shells 

 of this genus attain ; the valves sometimes exceeding four 

 feet in breadth, and of the enormous weight of five hun- 

 dred pounds ; but so disproportionate are the varieties of 

 this species, that some have been found measuring only 

 half an inch. This species is generally more or less rib- 

 bed and foliated, and sometimes imbricated or scaly; the 

 usual color is a dirty white, but the rarest varieties are 

 those which have a fine redpink, 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. The C. hippopus also deserves to be noticed ; like the 

 C. gigas it varies considerably in size, and is frequently 

 found a foot long, while some specimens do not exceed 

 an inch ; it is usually of a yellowish color, with pink 

 spots and murications. 



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

 posterior slope is usually open or gaping, and the anterior 

 closed, not unfrequently having its margin crenulate. 

 The valves are mostly inequilateral, one protruding be- 

 yond the other, and of tenappearing as if deformed. The 

 hinge has generally a callous gibbosity, inserted into an 

 oblique hollow. 



The C. concamerata is remarkable for having, in the 

 interior of each valve, an ovale chamber, which gives the 

 shell an appearance of being double. 



The more beautiful species of this genus are richly foli- 

 ated or spined, — as the C. lazarus, C. gryphoides, and 

 C. arcinellaj the varieties of which are sometimes wor- 

 thy of admiration. 



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



