544 MOLLUSCA 



Key to the genera of Viviparidae here described : 



! Shell banded, with umbilicus 1. VmPABA 



a, Shell not banded, without umbilicus. 



&! Shell thick and solid 2. CAMPELOMA 



b a Shell thin 3. LIOPLAX 



1. VIVIPARA Lamarck (Paludina Lam.). Shell thin, with about 5 

 whorls and a small umbilicus : 100 species, cosmopolitan ; about 8 Amer- 

 ican species, mostly in the southern states; about 2 on the Pacific slope. 



V. contectoides Binney (Fig. 847). Shell with 4 revolving brown 

 bands, of which 3 are on the body of the whorl and 1 on the base, the 

 upper whorls showing but 2 bands, sometimes indistinct or wanting; 

 length 33 mm.; width 25 mm.: eastern and central states, in lakes and 

 rivers, on muddy bottoms in shallow water. 



2. CAMPELOMA* Rafinesque. Shell solid, thick, with- 

 out umbilicus; whorls 6: about G species, all in North 

 America. 



Key to the species of Campeloma here described: 



ch Spire shorter than the aperture C. PONDEROSUM 



a a Spire and aperture of equal length. 



& x Whorls rounded C. DECISUM 



6 2 Whorls flattened C. SUBSOLIDUM 



C. ponderosum (Say) (Fig. 848). Shell very heavy and solid, con- 

 ical, with a very large lower whorl and an elongate ovate aperture; 

 color greenish or blackish; length 21 mm.; width 15 mm.; aperture 

 longer than the spire: New York to Illinois, south to Alabama. 



C. decisum (Say). Shell rather solid, conical; spire about as long 

 as the aperture ; length 28 mm. ; width 17 mm. ; color dark green, surface 

 shining: New England to Iowa; south to Tennessee. 



C. subsolidum (Anthony). Shell very solid, yellowish or light 

 green in color, smooth; whorls 6, flattened; aperture sigmoid; length 

 40 mm.; width 23 mm.: New England to Illinois, south to central Ohio. 



3. LIOPLAX Troschel. Shell thin, conical, and elongate; without 

 umbilicus; foot very large: 2 species, both in the United States. 



L. subcarinata (Say). Shell with 3 or 4 whorls, which are with 

 2 or 3 indistinct ridges; operculum spiral in the center, except in old 

 shells; aperture oval; length 12 mm.; width 10 mm.; color greenish: 

 New Jersey to Indiana. 



FAMILY 8. VALVATIDAE. 



Shell small, conical, and depressed or discoidal, with an open 

 umbilicus; operculum corneous, circular, multispiral; periostracum 



* See "On the Genus Campeloma," etc., by R. E. Call, Bull, Washburn Coll. Lab., 

 Vol. 1, p. 149, 1886, 



