198 



CONCHIFEXA. 



FIG. 199. PIN x.\. 



The third family of Conchifera embraces 



The Clams (Chamaced), in which the two sides of the mantle are conjoined 

 so as to leave three apertures, through one of which the " foot " is protruded ; 

 a second is for the entrance and expulsion of the water required for respira- 



FIG. 200. MUSSELS. 



tion, while through the third effete materials are rejected. These two last 

 openings are not prolonged into a tube or respiratory siphon. To this family 

 belong 



The Clam-Shells (Tridacne), the giants of the bivalve race. They live 

 attached by their byssus to rocks, shells, and corals. The valve of a large 

 individual forms a very picturesque basin for catching the clear falling water 

 of a fountain, which flows prettily through its deeply indented edges. In 



