114 P A L.EONTOLOGY OF THE UPPER MISSOURI. 



prominences at their outer bases. Gills internal, comb-like, single. 

 Tongue short; lingnal teeth in seven longitudinal rows (3. 1. 3), lateral, 

 more or less curved, truncated and serrate, or pointed and claw-shaped 

 at the extremit}-. Generative organs unisexual; in the male, included 

 in the right tentacle ; in the female, under the margin of the mantle on 

 the same side. Female ovo-viviparous. 



The following groups are included in this family, viz. : Viviparus, Tulotoma, 

 CampeJoma (or Melanlho of authors; not Bowdich), LiojjJax, and Lioplacodes. The 

 groups Larina, Palvdomus, Bithynia, Bithynella, Ganga, Tanalia, PldJopotamis, 

 and Rii-idina have also been placed here by some authors, but the labors of Prof 

 Gill and Dr. Stimpson have shoAvn that all these should be eliminated, thus leaving 

 the Ykiparidce probably a strictly ovo-viviparous group. 



Genus VIVIPARUS, Montfort. 



Synon. — Vivipare, Lamarck, Pliil. Zool. 1809, ii. 320 (without example, diagnosis, or figure) ; and again, in the 

 same way, Extr. d'un Cours. 1812. 

 Vieipiirus, Montfort, Syst. 1810, ii. 247.— Gray (in part). Proceed. Zool. Soc. 1847, part xv. 1,15; and 



again. Guide to Syst. Distr. Moll. Brit. Mus. 1857, i. 112; Gill, Proc. Acad. Nat. Sci. Phila. 1S(J3, 37. 

 Henterum, Hdbn. Epist. I. 1810. 



PahuUna. Lamarck, Extr. d'un cours. 1812 » * * ; and Hist. 1822, vi. 172.— Scuweigo. (part) Naturg. 

 1820, 736. — Blainville (part), Diet. Sci. Nat. 1824, xxxii. 320; and 1825, xxxvii. 300. — Deshayes 

 (part), Encyc. Meth. 1832, iii. 689, and of various later authors. 

 Vivipara, Sowerby, Mineral Conchology, 1813, tab. 31. — H. & A. Adams (part). Genera Recent Moll. 1854 

 i. 38. 

 Etym. — Vivus, alive ; parin, to bear or bring forth young. 

 Type. — Heltx vivipara, LiNN. 



Shell ovate or conic-subovate, thin, usually with a small umbilical perforation ; 

 volutions rounded or more or less flattened; surface smooth or with revolving lines 

 or carinas ; epidermis olivaceous, often with revolving bands of color ; aperture 

 more or less regularly ovate; outer lip thin, straight in outline, and continuous on 

 a plane with the inner. 



Operculum corneous, entirely annular. 



Animal with lateral teeth of the lingual ribbon oblong, arched, somewhat pointed 

 below, truncated and serrate above; median tooth shorter, curved, more or less 

 rounded, and serrate above; the middle denticle being larger than the others. 



Tlicse mollusks inhabit rivers, lakes, and other bodies of fresh water, and are 

 widely distributed in the Northern hemisphere. This genus is related to Carvpeloma, 

 Liojjlax, and Tulotoma, which have, indeed, until recently, been included in it, cither 

 as subgenera or otherwise, by most authors. It may be distinguished from the 

 former two groups, however, by its thinner shell, and by its outer lip being straight 

 in outline and continuous on a plane with the inner, instead of being inversely 

 sigmoid. A more important difference, however, is in the lingual teeth, which, in 

 Campeloma and Zjo^jZocc, "have the upper margins smooth, or only very minutely 

 serrated, while the outer two on each side are pointed and claw-shaped, instead of 

 truncated above. Lloplax is also distinguished by a subspiral opercular nucleus. 



