50 BIVALVES. CHAMA. 



bear a stiiking resemblance to a heart, excepting that the 

 valves terminate in a graceful curve towards the hinge. 

 The other is exemplified in the C. concamerata, which 

 has, in the interior of each valve, an ovate chamber. 



The species which compose the first division are de- 

 tached; and those of the second aflix themselves to 

 other substances, as rocks, stones, shells, &c. 



The colors are extremely various, sometimes elegant- 

 ly blended. Of the C. arcinella and C. gigas the pink 

 varieties are most valued by collectors. 



The most rare species are the C. moltkiana, C. se- 

 miorbiculata, and C. concamerata. 



The American, Indian, and Atlantic Oceans, and the 

 Mediterranean, Caspian, and Adriatic Seas, produce nu- 

 merous varieties of the orenus. 



The Chama is named from the gaping (yrvfiv) ob- 

 servable in two of its species. 



Division I. — Shell equivalve. 



The C. gigas is the largest shell in the order of 

 testacese ; the valves sometimes exceed four feet in 

 length, and are of the enormous weight of five hundred 

 pounds. So disproportionate are the varieties of this 

 species, that specimens have been found measuring only 

 half an inch. The cartilage of the hinge, which is of a 

 dull brown color, when cut and polished, is so beauti- 

 fully irridescent, that it even rivals the opal. 



This species occasionally produces large and costly 

 pearls. 



