MOLLUSCA. 



275 



earthy matter) than those of marine Mollusks, having to 

 be carried on the back without the support of the water. 



Fig. 232. — A, Land-snail (Helix); B, C, A Slugs {Limax) ; E, F, G, Pond-snails 

 (Limncea, Paludina, and Planorbis). 



Their eggs are laid singly, while the eggs of other orders 

 are laid in chains. 



They are found in all zones, but are 

 most numerous where lime and moisture 

 abound. All feed on vegetable matter. 

 A few are naked, as the Slug ; some are 

 terrestrial; others live in fresh water. 

 The Land - snails, represented by the 

 common Helix, the gigantic Bulimus, 

 and the Slug {Limax), are distinguished 

 by their four " horns," the short front 

 pair being the true tentacles, and the 

 long hinder pair being the eye-stumps. 

 They have a saw - like upper jaw for 

 biting leaves, and a short tongue covered with minute 

 teeth. The Pond-snails, as Limnaea and Planorbis, differ 



Fig. 233 Bulimus oblon- 



gus; one half natural 

 size. Guiana. 



