240 



SYSTEMATIC ZOOLOGY 



Of the aquatic genera, Limnaea (Fig. 246) is one of the com- 

 monest in our Northern states ; it has a sharply pointed shell, 



and is a host for the larval 

 stages of the flukeworms, 

 already described under the 

 Trematoda. Planorbis has a 

 flat spiral in a single plane, 

 and little fresh-water limpets 

 occur, very like the salt-water 

 species. The terrestrial Pul- 

 monata all have two pairs 

 of tentacles, with the eves 

 situated at the tips of the 

 posterior pair. A few of 

 them, mostly tropical species, 

 are carnivorous, feeding on 

 worms and on other Pul- 

 monata, but the majority are 

 plant-eaters. The largest 

 family of land snails is the 

 Helicidse, which is very 



Fig. 246 



water snail. 



Livinma stagnalis, common I 



(From Brehm's Thierleben.) 



widely distributed ; in the 

 tropics their shells are often very brilliantly colored. Two 

 species, Helix pomatia (Fig. 247) and Helix aspersa, are largely 

 eaten in Europe. In Brazil there is a very large species sold in 

 the markets, whose shell measures fifteen centimeters in length. 



8 9 



FlG. 247. Helix pomatia, :\ land snail. I, mouth; 2, anterior tentacles: 3, eve tentacles; 

 4, edge of mantle ; 5, respiratory pore ; 6. anus ; 7, apex of shell ; 8, foot ; 9, genital open- 

 ing. (Alter Shipley and MacBride.) 



