Some changes will undoubtedly be required in this 

 genus. It is not now to be admitted that the C conca- 

 merata, Brug. can remain in the same genus with the spe- 

 cies represented in our plate. Particularly as the remark- 

 able chamber which exists in that shell seems to be devot- 

 ed to a purpose altogether peculiar. On this subject the 

 late ingenious Miller wrote me as follows : "You have pro- 

 bably seen an account of the interesting discovery of the 

 use of the conic chamber or pouch in Chama concamerata ; 

 almost immediately after the statement was published, I 

 received specimens from the Cape, that not only shew the 

 eggs, but also minute shells, in the pouch." 



Some slight approach towards a similar form may be 

 found in the Jeson of Adanson and in the C. ru/escens, 

 Lam. and perhaps even in the C. calyculala^ L. and C. 

 crassa, Lam. which are included in the subgenus that 

 Blainville named Mytilicardia ; though it is hardly pro- 

 bable, that they can enter into the same group with the 

 concamerata. 



Lamarck has described twenty-five species, of which 

 three are fossil. 



CARDITA TRIDENTATA. 



DESCRIPTION. 



Shell suborbicular, subequilateral, thick and ponderous, 

 with about eighteen convex, longitudinal ribs, cancellate 



