OYSTERS. 



195 



The Conchifera may be classed in accordance with the follow- 

 ing table : 



/ Having the mantle open, and without tubes or special") Ostracea. 

 apertures ) Oysters. 



The first family of the Conchifera includes Oysters (Ostracea} ; 

 these have no foot, and the mantle is entirely open ; the shell is 

 irregular, thick and foliated, and is generally fixed to some foreign 

 body by the outer surface of one valve. The hinge is toothless, 

 and the ligament is internal. 



The Common Oyster. "The living luxury" is too well known to need 

 description. 



The Tree-Oyster (Ostrea arborea\ which in Africa is met with clinging in clus- 

 ters to the exposed roots of the mangrove-trees that fringe the margin of all the great 

 rivers in tropical climates, is, according to Adanson, as delicate and well tasted as our 

 own. The negroes lop off a branch loaded with the shells, obtaining, by one stroke of 

 the axe, a large supply, for if the branch has many offsets, the load will be enough for 

 any one man to carry. 



The Pile-Shells (Lima) usually live at the bottom of shallow seas, with 

 the valves widely extended and thrown flat back, like the wings of certain 

 butterflies, when basking in the sun ; but when disturbed, they start up, flap 

 their light shells, and move rapidly through the water by a succession of 

 sudden jerks. The cause of their alarm over, they bring themselves to an 

 anchor. When many hundreds of these curious bivalves are seen together 

 in the recesses of clear pools, surrounded by living branches of parti-coloured 

 corals, their crimson-spotted mantles and the fringes around them exhibit a 

 very rich and beautiful spectacle. 



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