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 Yenericardia and Oypricardia as subgenera ; 
both of which Lamarck had separated from Brugui^re’s genus 
Cardita. 
Yenericardia 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. Gyprieardia is also very 
similar ) it is remarkably inequilateral and has three teeth in each 
valve. Many of the species of Cardita resemble Gardimn 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 G. rufescensj Lam., and perhaps 
even in the G. calyculata, L., and C. crassa, Lam., which are included 
in the subgenus that Blainville named Mytilieardia ; 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. — Yenericardia tridentata, noh. Jour. 
Acad. Nat. Sci. vol. 5, 216. 
Ohs. 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 Gyprieardia modiolaris, a very entire 
specimen of which was sent to me by Mr. Hoeninghaus. Plate 40. 
