154 Contributions to Indian Malacology . [No. 2 



of the shell, prominence of the umbones, shape of the muscular im- 

 pressions, colour of the nacre, characters of the epidermis, &c. vary 

 ad infinitum — in short that species must be described like genera and 

 grouped around types, not distinguished by characters. 



I see from a notice in the Paris Journal de Conchyliologie that, in 

 the same volume of the American Journal of Conchology, Mr. Conrad 

 proposed a new genus Trigonodon for Monocondyl<%a crebristriata of 

 Anthony, from which, as I have stated above, Anodonta inoscularis, 

 Gould, is at the best but dubiously separable specifically. But the 

 last named shell is the type of Gould's genus Pseudodon, and Gould 

 himself suggested the identity of that genus with D'Orbigny's Mono- 

 condyloma* Unless Mr. Conrad has procured the animals of the Pegu 

 forms, and shewn them to be distinct from those of South America, 

 (and I scarcely think he can have done so,) I cannot believe that any 

 useful object is attained by inventing these generic appellations. Even 

 if Trigonodon be not Pseudodon over again, (Mr. Conrad appears to 

 have already furnished one synonym before for Pseudodon, viz. 

 Monodontina,) there has been no distinction of any generic value 

 shewn between the shells of Burmese and Malay species of Monocon- 

 dyl/za and those of S. America ; and bearing in mind that there are 

 some genera of more restricted distribution than those belonging to 

 the Unionidce, e. g. the Tapir, and amongst Mollusks, Cyclophorus 

 and Megalomastoma, common to the two regions, it would, I think, 

 be more scientific to examine the animals of the Burmese shells allied 

 to Monocondylcea, before founding new genera to comprise them. 



There is of course the possibility that Mr. Theobald may have been 

 misinformed as to the respective names of the two species, and that 

 the type of Trigonodon is the form I have referred to Monocondylcea 

 Vondenbuschiana. I can only add that the specimens of the same shell 

 from the same locality sent to me by Mr. Theobald, do not differ 

 more from Krister's figure of V. d. Busch's original specimen of M. 

 Vondenbuschiana in Martini and Chemnitz, than that figure does from 

 Lea's. 



Unio Pegtjensis, Anthony. 



American Journal of Conchology, Vol. I. 



I cannot learn what species has been thus named I hope to be 

 able to refer to the volume before long and to return to the subject. 

 * Ot. Conch., p. 194. 



