194 



Ohs. Poll informs us, that the animal resembles that of Ano- 

 donta and Unio ; and accordingly Blainville places the genus next 

 to that group with Venericardia and Cypricavdia as subgenera ; 

 botb of which Lamarck had separated from Brugui^re's genus 

 Cardita. 



Venericardia is much like the present genus, with which Sow- 

 erby unites it, and is chiefly distinguished by the teeth being all 

 oblique and directed towards one side. Cypricardia is also very 

 similar ; it is remarkably inequilateral and has three teeth in each 

 valve. Many of the species of Cardita resemble Cardium on their 

 exterior surface, but the insulated lateral teeth of the latter are an 

 obvious distinction. The three genera are certainly very closely 

 allied in nature. 



Some changes will undoubtedly be required in this genus. It 

 is not now to be admitted that the G. concamerata, Brug., can re- 

 main in the same genus with the species represented in our plate. 

 Particularly as the remarkable chamber which exists in that shell 

 seems to be devoted to a purpose altogether peculiar. On this 

 subject the late ingenious Miller wrote me as follows : '' You have 

 probably 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 speci- 

 mens 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. rufescens, Lam., and perhaps 

 even in the C. calycidata, L., and C. crassa, Lam., which are included 

 in the subgenus that Blainville named Mi/tilicardia ; though it is 

 hardly probable that they can enter into the same group with the 

 concamerata. 



Lamarck has described twenty-five species, of which three are 

 fossil. 



Cardita tridentata. — Venericardia tridentata, nob. Jour. 

 Acad. Nat. Sci. vol. 6, p. 216. 



Obs. The large recipient cavity of the hinge of the right valve 

 is somewhat similar, though wider in proportion, to that of the 

 corresponding valve of Cypricardia modiolaris, a very entire 

 specimen of which was sent to me by Mr. Hoeninghaus. Plate 4(>. 



