CRUSTACEA. 



UNDER this appellation ar.e arranged animals which have articu- 

 lated limbs, and are covered by an external crust. This crust is 

 earthy and brittle, and not stony like the shells of Mollusca. A 

 crab or a lobster will convey to the mind a general idea of the 

 characteristics of this class. The Crustacea inhabit both land and 

 water. Some of them are of considerable size, but the great 

 majority are very minute ; and the ocean literally swarms with 

 myriads which are too small to be noticed by the naked eye. A 

 single cup of sea-water, taken at random, will always be found to 

 contain some of them. All of them live upon decaying substances, 

 either animal or vegetable. They are naturally repulsive in their 

 appearance, though many of them are beautifully ornamented with 

 colors. Yet they are highly serviceable to man, both for the food 

 they afford him, and for the purity of the pool, the shore, and the 

 sea, which it is their province to promote. They are all edible 

 and palatable, even to man ; but to fishes they are a welcome as 

 well as an inexhaustible source of nutriment. The cod and had- 

 dock devour great numbers of crabs, and even the Greenland whale 

 is said to subsist mainly upon the minute Crustacea and accompa- 

 nying Radiata. 



Crustacea are distributed into Orders, according to the arrange- 

 ment and number of the legs. 



DECAPODA. 



Those which have five pairs of legs. 



GENUS CARCINUS, LEACH. 



C. M.ENA8, Li5. Carapax granulate, with five lateral teeth; 

 front three lobed. 



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