SEA SNAILS. 25 



Such shells are called canal iculated shells. 



The aperture of the shell is said to be entire, when it 

 does not possess this notch, or canal. Let the pupil separate 

 the shells having the aperture entire, from those shells hav- 

 ing a canal. 



These differences in the shell, as slight as they appear, 

 are accompanied by corresponding differences in the charac- 

 ter and habits of the animal. 



Those snails having the aperture of the shell entire are 

 with few exceptions vegetable-feeders, while those having a 

 canal to the shell are flesh-feeders. The mouth-parts, and 

 opercula, too, are different in the two groups. 



24. Other shells will be found differing greatly in appear- 

 ance from those thus far studied. One of these is repre- 

 sented in the lower left-hand corner of Fig. 26. 



Another species, called the limpet, looks like this (Fig. 



30): 



FIG. 30. SHELL OF LIMPET. 



These shells will be found sticking with great tenacity to 

 the rocks, and some skill and force will be required to 

 remove them. This can be done by using the large blade 

 of a pocket-knife, and suddenly scraping them from the rock. 

 If they are then placed in a saucer of water, with the shell 

 downward, the animal within will be found to have the 

 broad, creeping disk, head, tentacles, and other parts, peculiar 

 to the snails already studied. 



