CHAPTER LXXIV: THE POND SNAILS 

 Family LiMi^JEwm 



Shell fragile, variable in form, horn-coloured, usually with 

 an oblique fold on the columella; outer lip simple, acute. Head 

 with broad muzzle, dilated at the end; mouth with one or more 

 jaws, radula armed with numerous quadrate teeth; tentacles 

 flattened, eyes sessile at inner bases of tentacles; foot flat; res- 

 piratory orifice on right side. Sexes united. 



Fresh water mollusks, which come to the surface to breathe 

 fresh air, and feed on confervae and other aquatic plants and 

 small animal forms. They form an important staple in the diet 

 of fishes, frogs, toads and birds, including coots, rails and others 

 that frequent ponds and streams. In winter they bury themselves 

 in mud. Distribution universal. 



Genus LIMN^A, Linn. 



Shell dextrally spiral, oblong, translucent, with thin epi- 

 dermis, last whorl large; aperture large, roundish; lip simple; 

 columella with one oblique fold. Tentacles flattened, triangular; 

 mantle edge thickened; foot short, rounded. A world-wide 

 genus, preferring the north temperate zone. In North America 

 it reaches its maximum size in the region of the Great Lakes. 



Left-handed Limnaeas occur in the Sandwich Islands and 

 New Zealand. The genus is represented in hot sulphur springs 

 in Iceland, and in Lake Geneva at a depth of 800 feet. A species 

 is found in Thibet at an altitude of 14,000 feet. Another creeps 

 over ice fields in northern Asia, and is frozen in solid blocks of 

 ice ten months in the year. 



The Great Pond Snail (L. stagnalis, Linn.) has spread 

 from Europe throughout the northern hemisphere. In North 

 America it is found in still water and in quiet streams from Green- 

 land to Alaska and south to Texas. In winter it is frequently 

 seen creeping along the under side of the icy crust of a brook. 



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