510 



MOLLUSCA 



noitlieni states from New York to the Pacific, also in the middle central 

 and western states; often common. 



L. palustris (0. F. Miiller) (L. elodes Say) (Fig. 778). Shell from 

 pale brown to black in color, elongate, conical, with an acute apex which 

 is sometimes broken off and with rather more than 6 whorls, which are 

 decidedly convex; aperture shorter than the spire with an acute lip and 

 a white callus on the parietal wall; length 30 mm.; width 12 mm.: 

 circumpolar; northern America; the commonest species; Europe. 



L. obrussa Say. Like the above, but shell with only 5 whorls and 

 a larger aperture, and very much smaller: New England to Kansas; 

 California; common about the muddy margins of ponds. 



Fig. 776 Fig. 777 



Fig. 776 — Lymnwa stagnalis (Baker). 1, foot; 

 (Baker). Fig. 778 — Lymna: 



Fig. 77! 



I, tentacle. Fig. 777- 

 palustris (Baker). 



-Lymnwa reflexa 



L. catascopium Say. Shell broad and robust, usually reddish or 

 blackish with 4 to 5 whorls, the last large and very convex, with a large, 

 flaring aperture; length 17 mm.; width 12 mm.: northern and central 

 states; common in large rivers and lakes. 



L. humilis Say. Shell small, thin, and transparent, with 5 or 6 

 whorls, 8.5 mm. long, regularly conical and somewhat elongate, variable 

 in color, sometimes blackish; distinct umbilicus present: entire eastern 

 and central America, on the muddy banks of streams. 



L. auricularia (L.). Shell large, with a very short, acute spire 

 and a very large, ear-shaped aperture, which takes up almost the whole 

 shell ; length 33 mm. ; width 25 mm. : an European species, introduced 

 locally in many eastern localities. 



L. cape rata Say. Shell rather solid, yellowish to black in color, 

 with 5 to 6 Avhorls, with numerous minute revolving lines, 15 mm. long, 

 7 mm. wide: New England to California and northwards. 



Family 3. PHYSIDAE. 



Shell sinistral, thin, with an acute spire, a large lower whorl, and a 

 large oval aperture, with an acute lip and a wide callus on the parietal 

 wall; jaw a single piece, foot pointed behind; tentacles filiform: over 

 150 species; cosmopolitan; about 22 in this country; in swamps and 

 ponds. 



