GASTROPODA. 



27 



The freshwater Limpets {Ancylm) live attached to stones and 

 leaves of plants, and have not the habit of floating, bnt, like the 



Fig. 22. 



British Pond-iSnail (^Limnsea stagnalis). 



1. Upper view: «, foot; &, tentacles: c, eye; c?, muzzle. 



2. Lower view: letters a, h, c as above; e, mouth; /, respiratory orifice. 



rest of the Limnceidce, feed on freshwater algte, confervte, and 

 decayed vegetable matter. 



{Stylommatophora.) 



True Snails (Helicidce, etc.) have a distinct head furnished with Cases 

 eyes, tentacles, cutting upper jaws, and rasping teeth, and nearly all ^^'^'^ ^' 

 are protected by a spiral shell. They are almost exclusively vegetable- 

 feeders, subsisting chiefly on leaves. The sexes are not distinct. 

 Many of the species are beautiful objects on account of the brilliancy 

 of their colouration, and some are remarkable for the variation they 

 exhibit in this respect. Species of Helicidce, are found in nearly 

 every part of the world and in all situations, from sea-level to an 

 altitude of 12,000 feet. They are fond of moisture, and in hot and 

 dry weather retire within their shells, remaining torpid until the 

 return of dew and rain. Helix pomatia (Case 119), which is found 

 on the chalk in the south of England and on the Continent, is 

 commonly eaten in Austria, France, and Belgium. 



