MOLLUSCA. 
275 
earthy, matter) than those of marine Mollnsks, having to 
be carried on the back without the support of the water. 
Fig. 232 — A, Land-snail (Helix); P, <7, D, Sings (Limax) • E, F, G, Pond-snaiis 
(Limncex, 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, 55 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 Limncea and Planorbis , differ 
Fig. 233. — Bulimus oblon- 
gus; one half natural 
size. Guiana. 
