70 GENUS XII. CHAMA. 



Chama Cor is a smooth heart-shaped shell, and differs much 

 from all the others ; it has two teeth, with a deep hollow under 

 the beak, and a lateral tooth under the Hirther end of the 

 cartilag-e in one valve, and one tooth under the beak and a 

 lateral one at the end of the cartilage in the other. Chama 

 Moltkiana and one or two more are described as varying from 

 the rest in their teeth ; they are but little known ; the cartilage 

 is external in all the species, but in some it is sunk in a hollow 

 groove so as to be scarcely visible on the outside. In some 

 species, as Chama Cor, the beaks are raised above the surface 

 of the shell in a spiral form, somewhat resembling the horn of 

 an animal. 



Linnaeus has described 14 species, Gmelin has added 11, 

 and Dr. Turton none. Total, 25. 



Lamarck has divided this genus into five, as follows : 

 Tridacna. Shell sub-transverse and ineqiiilateral ; the hinge 

 with two compressed teeth inserted, the posterior depres- 

 sion gaping (see Chama Gigas, f. 31). 

 HiPPOPUH. Shell sub-transverse and inequilateral ; the hinge 

 with two compressed teeth inserted, the posterior depres- 

 sion closed (see Chama Hippopits, f. 3^). 

 Cardita. Shell inequilateral ; hinge with two unequal teeth : 

 the one which is short is vmder the beaks, and the other 

 lengthened beneath the cartilage (see Chama antiquata, 

 f. 33). 

 IsoCARDiA. Shell heart-shaped ; the beaks distant, turning to 

 one side and diverging; the hinge with two teeth, flattened 



