518 MOLLUSCA 



C. lubrica (0. F. Muller) (Fig. 795). Shell 6 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 jtulcliella (Sterki). 

 Fig. 797VaUowacostata (Sterki). 



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

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

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

 other dark, damp places. 



V. costata (Mull.) (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. 



STJCCINEA 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. 



&! Aperture wide and oblique S. OVALIS 



fcj Aperture long, narrow, and straight S. RETUSA 



a a Aperture round, occupying a little over half of the shell S. AVABA 



S. ovalis Say (S. obliqua 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. 



