314 INTRODUCTION^ TO CONCHOLOGY. 



Tamity VII. Naiades. 



These dwell in rivers, such, as winding sweep 

 Through vast savannahs or primeval woods. 

 Where range the pumas, and the crested snake 

 Coils in his green abode. 



This family includes a numerous and cliaracteristic group 

 of fiuviatile mollusks, chiefly inhabiting the great rivers 

 of America. In consequence of the gradual and perfect 

 link which holds this family in connection, five genera are 

 considered as best calculated to simplify aU previous 

 arrangements, namely, Unio, Hyria, Anodon, Iridina, and 



The animal inhabitant appears to be nearly the same 

 in each, excepting in the genus Iridina, where he is 

 provided with two tubes or syphons, formed by the pro- 

 longed union of the under portion of the syphon. The 

 shell is inequilateral, having the valves connate or free, 

 covered with a thick olivaceous epidermis, and more or less 

 eroded at the umboes. The hinge is very irregular, with 

 generally two or more very thick solid teeth, often none, 

 and the valves are united by a strong ligament ; the anterior 

 muscular impression is always compound, showing the 

 marks of one or more accessory cartilages of attachment. 



