290 



THE INHABITANTS OF THE SEA. 



Pteroceras Scorpio. 



overturned. 



is by creeping along on their foot: those that have a very heavy 

 house to carry, such as the Cassis or the 

 Pteroceras, generally move along very 

 slowly, while others, such as the Olivae, 

 that are possessed of a comparatively 

 strong and broad foot, have rapid and 

 lively movements, and quickly raise 

 themselves again when they have been 

 The Strombidse and Rostellarise place their power- 

 ful and elastic foot under the shell in a bent 

 position, when suddenly by a muscular effort 



they straighten that organ and roll and leap over 

 ohvahispiauia. and oyer> The structure of the foot of the 



Tornatella fasciata, an inhabitant of our coast, is most remark- 

 able: beaten incessantly by the waves, in 

 the cavities of rocks which it frequents, 

 nearly on a level with the surface of the 

 sea, to the violence of which it is always 

 exposed, it has need of additional powers 

 for retaining its hold ; its foot is therefore 



Strombus pes pelicani. ,. . , . . , „ . .. * , 



divided into two adhering portions, placed 

 at each extremity, and separated by a wide interval ; when it 

 crawls, it fixes the posterior disc and advances the other, which 

 it attaches firmly to the place of progression, and this being 

 effected, the hinder sucker is detached and drawn forwards, 

 locomotion being accomplished by the alternate adhesion of 

 these two prehensile discs. In Cyelostoma the foot is likewise 

 furnished with two longitudinal adhering lobes, which are ad- 

 vanced alternately. But the foot of the marine snails is not 

 merely an instrument of progression on a solid surface, for in 

 many species it is convertible at the will of the animal into a 

 boat, by means of which the creature 

 can suspend itself in an inverted position 

 at the surface of the water, where by 

 the aid of its mantle and tentacles it can 

 row itself from place to place. 



The Ianthinse, or purple Sea-Snails, 

 carry under their foot a vesicular organ 

 like a congeries of foam-bubbles, that prevents creeping, but 

 serves as a buoy to support them at the surface of the water. 



Ianthma communis. 



