4.76 CRETACEOUS PELECYPODA 



becomes closed in the adult shell. The same author also says that there are three 

 species known, adding "America ?" as locality. 



Sowerby's type species of Hemiplactma CEozieri, G. B. Sow.), figured in 

 Descript. sc. de I'Egypte, is probably the same species as Cantraine's. Gray, in 

 describing the genus (Proc. Zool. Soc, 1819, and Cat. Flacent. and Anom. Brit. 

 Mus., 1850, p. 4), says that on the inner surface of the right valve, just in front 

 of the base of the process which supports the cartilage, there is a small, shallow, 

 roundish jnt with a short fuiTOW towards the centre of the shell, which is evidently 

 a rudimentary representation of the sinus found in the genus Anomia. This 

 rudimentary sinus is not visible on the outer surface of the shell. Cantraine 

 makes no reference to the pit or groove, but the latter is distinctly indicated in 

 his figure of the flatter valve. 



5. Pododesmm, Phil., 1837, (Handb. der Conch., p. 380). Irregular, in, 

 equivalve, with dissimilar umbones, that of the lower, flatter, and adnate valve 

 spirally twisted, with a raised lamella, separated from the margin, bearing the 

 ligament which is lodged in a corresponding groove of the other valve ; muscular 

 scar oval. Type, P. deciplens, Phil., from Cuba. 



Gray, Be eve, and other authors identify this species with Placimanomio rudls. 

 Brod. and H. and A. Adams quote this last species, besides two others, under 

 the name Pododesmus, as sub-genus of Placunanomia. I am not aware that the 

 specific identification of P. rudis and Philippi's type of Pof7o(fe«»ms has been 

 satisfactorily proved, namely, that the latter should be an advanced stage of age 

 of the former; but Philippi distinctly says that it differs "from Placunanomia 

 by the lower valve not being perforated, by the want of the two internal hinge 

 teeth," &c. I can hardly believe that in the face of such an assertion Philippi 

 would have overlooked the perforation of the lower valve of PI. rudis. 



The characteristic of Pododesmus very closely coincides with that of Conrad's 

 cretaceous Paranomia. 



6. Placunanomia, Brod., 1832. Irregular, inequivalve, attached by the 

 lower, flatter valve which has a perforation near the upper end, the anterior part 

 of the valve being somewhat twisted and produced into a bilobed raised tooth on 

 which the ligament is sitviated, and which corresponds to two ligamental grooves 

 of the other valve ; muscular scar single in the lower, double in the upper valve. 

 Type, P. macrochisma, Desh. 



Beeve described in 1859 (Iconica, vol. si,) 14 recent species; they are mostly 

 from the American and Australian seas. H. and A. Adams quote 12 species and 

 place three of them in Pododesmus, of which they call rudis the tyjie, possessing a 

 small foramen, and for the rest they adopt the sub-generic name Moiiio, Gray, 

 having a larger foramen, slightly embracing the large and thin plug. The dis- 

 tinction seems to me quite unnecessary. 



The difference of Carolia from Paranomia rests almost only in the absence 

 of perforation in the lower valve of the former genus. 



