518 MOLLUSCA 



C. lubrica (0. F. Miiller) (Fig. 795). Shell G mm. high, with 6 

 whorls, and yellowish in color: circumpolar; often common under dead 

 leaves or decaying bark. 



Family 4. VALLONIIDAE. 



Shell minute, with a low depressed spiral, widely umbilicate, con- 

 sisting of 3 or 4 whorls, the last of which is large and cylindrical; 

 ureter straight: 1 genus. 



Vallonia Risso. Aperture edentate, round; peristome reflected 

 and white ; jaw with numerous slight transverse ribs : 9 American species. 



Fig. 795 Fig. 796 Fig. 797 



Fig. 795 — Cochlicopa lubrica (Binney). Fig. 796 — Vallonia pulchella (Sterki). 

 Fig. 1{)7— Vallonia costata (Sterki). 



V. pulchella (0. F. Miiller) (Fig. 796). Height 1.3 mm.; diameter 

 2.6 mm.; shell thin, light colored, and transparent: circumpolar; north- 

 ern states; often very coninion, under sticks, stones, and logs and in 

 other dark, damp places. 



V. costata (Miill.) (Fig. 797). Height 1.3 mm.; diameter 2.7 mm.; 

 shell with regularly recurring transverse ribs; color gray: circumpolar; 

 northern states. 



Family 5. SUCCINEIDAE. 



Shell very thin, with a small spire and a large, often flaring aper- 

 ture; anterior tentacles very small or wanting; jaw with an accessory 

 quadrangular median piece : 6 genera, 3 American. 



SucciNEA Draparnaud. Shell fragile and transparent and not too 

 small to contain the body; tentacles short and thick; foot broad; ureter 

 reflexed: 200 species, on plants in wet places; 25 American species. 



Key to the species of Succinea here described : 



«! Aperture occupying the greater part of the shell. 



&i Aperture wide and oblique S. OVALIS 



?>a Aperture long, narrow, and straight S. retusa 



«j Aperture round, occupying a little over half of the shell S. avaba 



S. ovalis Say {S. ohliqua Say) (Fig. 798). Shell ovate, pale green 

 or yellowish and shining, and minutely striated, with 3 whorls; spire 

 small ; aperture oblique and very large ; length 28 mm. : eastern and cen- 

 tral America ; very common. 



