56 BIVALVES. — CHAMA.. 



and sometimes imbricated or scaly; the usual colour is a 

 dirty white, but the rarest varieties are those which have a 

 fine red-pink, or yellow tinge. Some of them, when per- 

 fect, are highly prized. The cartilage of the hinge has a 

 dull brown colour, 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 de- 

 serves to be noticed; like the C. gigas it varies consider- 

 ably in size, and is frequently found a foot long, while 

 some specimens do not exceed an inch ; it is usually of a 

 yellowish colour, 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 beyond the 

 other, and often appearing as if deformed. The hinge 

 has generally a callous gibbosity, inserted into an oblique 

 hollow. 



The C. concamerata is remarkable for having, in the in- 

 terior of each valve, an ovate 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. 

 arcinella; the varieties of which are sometimes worthy of 

 admiration. 



It seems a principle with the Chamse, (like the Spondyli), 

 to affix themselves to any extraneous substance which ac- 

 cident may throw in their way. They often adhere to 

 rocks, stones, and various shells; but, in many instances, 

 they seem to have a preference for some particular genus 

 of shells; for the C. arcinella is most commonly found af- 

 fixed to that species of Murex called the Thorny Woodcock; 

 however, it retains a partiality for others of the Murices, 

 especially those often known under the name of Triplices, 



