MOLLUSCA. 71 



beard or Lead, the hair will fall off. These mollusks 

 crawl about on the rocks like snails. The odor, how- 

 ever, is intolerable, whether the creature is brought into 

 the house or thrown upon the strand. 



THIRD ORDER. 



BIVALVES 'OR THE TRUE MUSCLES. 



This class of mollusca are inclosed in hard calcareous 

 shells, have no distinguishable head ; a few of them ad- 

 here closely to the rocks, without ability to move from 

 the spot ; others have a pedicle or foot, which is a fleshy 

 mass, somewhat resembling the tongue of a mammal, and 

 can be protruded oiitside of the shell, and serves for 

 motion along the bottom of the water; the progress, 

 however, of all this class is slow. When waiting for 

 food, the bivalves open their shells slightly, but no sooner 

 does a worm or other eatable article come within reach, 

 than the shell is again tightly closed. On the approach 

 of an enemy the same sudden shutting up of the defend- 

 ing shell is observed ; and when taken from their native 

 waters, they keep so tightly closed up, that not a drop 

 of the liquor usually found inside can escape. A few of 

 them spin, it is imagined, with their foot a bundle of 

 silk-like filaments, by means of which, like anchor- 

 cables, they affix themselves to submarine bodies. Those 

 which sit fast on the rocks have no foot. The first of 

 this order, 



The Common Oyster (ostrea edulis), is somewhat 

 elliptical, about as broad as a hand, and consists of a 



