BIVALVES. CHAMA. 55 



DIVISION II. SHELL UNARMED. 



FAMILY 1. Upper valve longitudinally striated. 



Anacanthus Spineless. 



FAMILY 2. Valves longitudinally plaited. 

 Plicatus Plaited. 



CHAMA. CLAMP, CLAM, OR GAPER. 



Animal a Tethys: Shell bivalve, rather coarse; hinge with 

 a callous gibbosity, obliquely inserted in an oblique hol- 

 low; anterior slope closed. 



THIS genus is by no means numerous, containing only 

 twenty-seven species, which, for the most part, are rough 

 and uncouth looking shells. The C. cor is, however, an ex- 

 ception, it being usually smooth: from its beauty and pe- 

 culiarity of structure, it is signalized from every shell in the 

 numerous catalogue of Bivalves. This species, which va- 

 ries in size from two to five inches in diameter, bears a 

 strong resemblance to a heart; its top being surmounted 

 by beaks which wind round towards the hinge in the most 

 graceful curvature possible. 



The genus Chama affords a subject for amazement ra- 

 ther than admiration, for some of its species grow to an un- 

 common size: the 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 its varieties, that 

 some have been found measuring only half an inch. This 

 species is generally more or lesss ribbed and foliated, 



