30 



SHELL GALLERY. 



PULMONATA. 



["Cases These Cases contain the vast assemblage of true air-breathers. 



12g-17d.] Common Land-Snails (Helicidce), Slugs (Limacida) , certain groups 

 of freshwater Snails {LimnceidcB), and a few marine Limpet-like 

 Snails (Siphonariidce) are the principal types of Pulmonates. About 

 10,000 species are known. True Snails (Helicidce) have a distinct 

 head furnished with eyes, tentacles, cutting upper jaws, and rasping 

 teeth, and all are protected by a spiral shell. They are almost ex- 

 clusively vegetable-feeders, subsisting chiefly on leaves. The sexes 

 are not distinct. Species of Helicidce are found in nearly every 

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

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

 dry weather retire within their shells, remaining torpid until the 



Fig. 19. 



British Land-Snail {Helix po media). 

 a, eye-bearing tentacles ("horns") ; b, lower or smaller tentacles. 



"Case 

 12 a] 



return of dew and rain. Helix pomatia, which is found on the 

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

 eaten in Austria, France, and Belgium. 



The eggs of Land-Snails vary in texture, size, and in numbers; 

 they are usually white, but in some instances yellow and pale 

 green. Those of some of the large South- American forms are as 

 hard as that of a hen, and more than an inch in length. 



Slugs are very like Snails without external shells; most of them, 

 however, possess a small internal shelly plate, or a few calcareous 

 granules hidden beneath the skin of the back. Some have a large 

 slime-pore at the end of the foot, and others are slightly phos- 



