GASTKOPODA. 
27 
The freshwater Limpets (Ancylus) live attached to stones and leaves 
of plants, and have not the habit of floating, but, like the rest of 
Fig. 22. 
British Pond-Snail (Limnsea stagnalis). 
1. Upper view: a, foot; 6, tentacles; c, eye; d, muzzle. 
2. Lower view : letters a, b, c as above ; e, mouth ; /, respiratory orifice. 
the Lim/iceidce, feed on freshwater algae, confervse, and decayed 
vegetable matter. 
(Stylommatophora.) 
True Snails (ffelicidce, etc.) have a distinct head furnished with Cases 
eyes, tentacles, cutting upper jaws, and rasping teeth, and 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 then' 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 Ed gland aud on the Continent, is 
commonly eaten in Austria, France, and Belgium. 
