30 



with the thinness and general aspect of the shell, I am led to 

 refer it to the genus Thyatirn, (Leach) Lamarck, 1818. If we 

 adopt Turton's name, it should be written Cryptodon bisectus ; 

 or, following Sowerby, it would be Axinus bisectus. 



252 = Isocardia fraterna, Say, Jour. Acad. Nat. Sci. Phila. IV, 143 ; 



( = /. rus^ica, Conrad). I do not adopt Bucardia, Lister, 1678, 

 on account of its ante-Linusean date, nor Isocardia, Lamarck, 

 1799, because Polis' name Glossus 1795, has priority. 



253 = Isocardia Markoi, Coxrad, Bui. Nat. Inst. 193, 2, 1. 



260= Cardium modestum, Conrad. Mr. Carpenter suggests that this 

 may be the joung of the recent Cardium biangnlatum. In this, 

 however, he was misled by a very imperfect figure, for I find, 

 on comparison, that the two shells are very distinct in form^ 

 and other surface cliaracters. 



276 — Mr. Gabb described this shell as a Miocene species (Proceed. Acad. 

 Nat. Sci. Phila. 1861) under the name Venus rliysomia. It is 

 now believed by him and Mr. Carpenter to be identical with 

 the recent Veieus (^Trigona) tantilla, Gould. 



282 = Venus athleta, Co.nrad, Proceed. Acad. N. Sci. 1862, 586. 



283 = Venus alveata, Conrad, Mioc. Foss. 9, 5, 2. 



284 = Venus latilirata, Coxrad, ib. 68, 38, 3. 



287 = Venus angustifrons, Conrad, U. S. Expl. Exp. X, 724, 17, 11. 



288 = Venus brevilineata, Conrad, ib. Fig. 13. 



289 = Meretrix decisa, Conrad, Pacific R. R. Rept. V, 323. 

 297 = Cytherea oregonensis. Conrad, Am. J. Sui. V, (2), 432. 

 302=Meretrix tularana, Conrad, Pacific R. R. Rept. V. 323. 

 304 = Meretrix uiiiomeris, Conrad, ib. 



306 = Cytherea vespertina, Conrad, Am. Jour. Sci. Vol. V, (2) ] 848,433. 



358 — This is certainly not a Donax, but doubtless a Solemya, as suggested 

 by Mr. Woodward (Brit. Asso. Rept. 1856, 366), and should 

 have been printed Solemya protexta in the list. It is clearly 

 distinct from its associate S. ventricosa, Conrad. 



367 — Mr. Conrad originally described this and the other species of SpisuUi 

 in the list, under the name Mactra, and subsequently referred 

 them to Ile.mimactra. He now agrees with me that Gray's 

 name Spisida should be retained for this group, and authorized 

 me to make the changes in his name. 



410 = Glycimeris estrellanus, Conrad, Pacific R. R. Rept. VII, 194. 

 Mr. Carpenter (Brit. Assoc. Rept. 1863) refers this species with 

 doubt, to the recent PanopBea generosa, Gould. The fossil is 

 only known from a single imperfect cast, giving no idea of its 

 internal characters. It is much smaller than the recent species 

 alluded to, but resembles it in form, not more, however, than 

 it resembles other fossil species, which from their geological 

 position must be distinct, and would not be suspected to be iden- 

 tical with any living species. The P. generosa- ngrees more 



