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BIVALVES MACTRA. 



The hinge of the Mactra is its best distinction from all 

 the other genera of Bivalves, for the middle tooth is al- 

 most invariably complicated, and of a triangular form, 

 having a small hollow on each side of it ; the lateral teeth 

 are remote from the beaks and inserted into each other. 

 The hinge of the Mactra, though very articulate, is re- 

 markably thin and delicate; in' some cases, the teeth 

 which compose it, are much thinner than paper. The 

 Mactrse are mostly equivalves; the interior margin is 

 rarely crenate or toothed. 



The Northern and European seas supply many of the 

 species of Mactrte. 



The Indian and American oceans also produce them ; 

 some are found in the Mediterranean, and others are in-t 

 debted to the Cape of Good Hope and African shores foir 

 their subsistence. They are also frequently found at the 

 mouths of rivers. 



