96 



D1CERAS. 



A fossil genus nearly approximating the genus Cha- 

 ma from which it differs by being regular, equivalve, 

 never attached by the lower valve, and the distinct 

 character of the hinge. Only one species known to 

 LaMarck. 



CHAMA. 



CHAM A LAZARUS. Lhlll. 



Sowerbys Genera, No. 7, pi 1 , fig. 3. 

 LaMarck has separated these shells from the G. Cha- 

 ma of Linnaeus, and associated in this genus such of 

 them only as possess a thick oblique transverse tooth, 

 resembling a lengthened callosity, in general crenulat- 

 ed or grooved, fitting into a corresponding cavity in the 

 lower valve: the shell is inequivalve, irregular, heavy, 

 rough, scaly or spinous; having the faculty of affixing 

 itself to other bodies, or to each other, by means of its 

 lower valve. Apices unequal and recurved : hinge, one 

 thick oblique tooth, subcrcnated, articulating into a ca- 

 vity of the opposite valve; two distant lateral muscu- 

 lar impressions; ligament external and inserted. The 

 characters of these shells in some respects ally them to 

 the G Diceras, and in others to the G. Etheria. 



