PHYLUM MOLLUSCA 



241 



perhaps opaque shells. Certain species, such as Polygyra roemeri, 

 P. alholahris and P. texasiana are capable of repairing broken shells 

 if the damage is not too severe. 



Body. — The body of the snail consists of a head, neck, foot, and 

 visceral hump. The head of a land snail (Helix) has one pair of 



Vemetus spirgtus 

 {Worm shelf) 



Limacina ausMb 

 (Ptefopod) 



Muxextenuispina 

 [Venus's comb) 



, Urosalpinx , 

 {Oyster drill) 



. Aeolis 

 (sea slug) 



Teredo navalis. 

 (Ship worn) 



Fie:. 133. — Marine mollusks. 



true tentacles which are probably sensitive to contact and smell, and 

 a pair of stalked "eyes" which can possibly detect different light 

 intensities, but are not sight organs. Our common genera of water 

 snails (Lymnaea, Physa, Helisoma) have their eyes situated at the 



