WHITE.] GENERAL DISCUSSION. 479 



Transactions of the American Philosophical Society, Yol. IX, p. 267, 

 Plate 37, Fig. 87, which Mr. Conrad stated in Proc. Acad. Nat. Sci. 

 Philad. 18G2, p. 567, to be identical with the Paludina subglobosa. of 

 Emmons (Geology of North Carolina, p. 273, Fig. 186). This assumed 

 identity is doubtful. The latter is probably either a Viviparus or a 

 Campeloma. The former is probably neither. 



From the Eocene strata of Wilmington, North Carolina, Sir Charles 

 Lyell obtained the natural cast of a shell which he referred to Paludina 

 and published (Jour. Geol. Soc. Lond., Yol. I, p. 431) a figure of it, but 

 without a specific name. Conrad subsequently (Am. Jour. Conch., Yol. 

 I, p. 32) gave the name Viviparus lyelli to this form. It is probably a 

 true Viviparus, but its characters are not sufficiently known to settle 

 the question definitely. 



In Fremont's Keport on Oregon and Northern California, pp.308, 300, 

 Plate III, Professor Hall has figured and described several forms which 

 have not been mentioned in the body of this article. They probably 

 belong to a fresh-water fauna, although it was supposed that they were 

 of marine origin when they were described. The specimens he had were 

 evidently imperfect, but I have never seen them, and I have been una- 

 ble by aid of Professor Hall's descriptions and figures to identify the 

 species which they represent among any collections made in the West. 

 The following are the names given them by Professor Hall in the work 

 cited: Nucula impressa (?), Cytherea parvula, Plemotomaria uniangulata, 

 Cerithium fremontij Natica(f) occidentalis, and Turritella bilineata. 



In Yol. Ill, p. 10, American Journal of Conchology, Mr. T. A. Con- 

 rad published a description and figure of a shell from the Carbonifer. 

 ous strata of Kansas, under the new generic name of Prisconaia, refer- 

 ring it to the Unionidae. It is probably a species of Schizodus, and there- 

 fore belongs to the Trigoniida3. 



In Yol. YI, of the same Journal, Conrad described Melania decursa 

 and Anodonta decurtata u from Colorado." Because he did not state any 

 locality or formation from which they were obtained, these species are 

 not include in the text of this article. The former is probably from 

 Oregon and identical with M. taylori Gabb. 



GENERAL DISCUSSION. 



Upon the preceding pages I have presented a synopsis of all the 

 known fossil non-marine mollusca of North America, in the course of 

 which it has been shown that many of the types now recognizable 

 among the living non-marine mollusks have great antiquity ; but that 

 certain of the types which have been recognized only among the fossil 

 species, and are therefore regarded as certainly extinct, were contem- 

 poraneous with many of those which survived. Before closing this 



