DIPLODONTA. 65 



simple at the edges ; siphons wanting (?) ; branchial lamellae 

 on each side of the body not united into one ; labial palps 

 developed, triangular ; foot lanceolate. 



This genus was established by Bronn for some fossil 

 shells from the tertiaries of Italy, including the Venus 

 Iwplnus of Brocchi. Mr. Gray considers it identical with 

 the genus Mysia of Leach's manuscripts, but Bronn, in 

 1831, was the first to define clearly and restrict the species 

 of this very natural group, and Mysia was not published 

 with a definition until 1833. Our British example of it 

 has been bandied from Tellina to Lucina and back again, 

 finding a brief resting-place in Psammobia on the way, 

 without having really very intimate affinity with any of 

 them. With the Tellinida: it certainly has no relations ; 

 with Lucina we associate it provisionally, for, as will be 

 seen presently, the account of its animal, now first made 

 known by Mr. Clark, presents anomalies not reconcilable 

 with the usual features of the tribe : so peculiar, indeed, 

 that we would earnestly call the attention of malacologists 

 to a minute examination of this curious mollusk. Possibly 

 it should be considered a member of the next tribe. 



Several species inhabit the Mediterranean, and some 

 extinct forms are found in the tertiary beds of the same 

 region. Mr. Hanley has a Diplodonta from the West 

 Indies, which seems exactly the British species. Philippi 

 describes one from Mazatlan (D. obliqua), and Dunker two 

 (circularis and Gruneri) from Western Africa. 



VOL. II. 



