310 IN^EODrCTIO>' TO CONCHOLOGY. 



are exhibited in the interior, at the lateral extremities of 

 each valve. 



The shell of Chamacea is characterized as being irregular, 

 inequivalve, and always attached by one valve to some other 

 substance. The hinge consists of a single tooth, though 

 occasionally obsolete. Two genera only are referred to this 

 family, Etheria and Chama ; the former inhabiting rivers, 

 the latter peculiar to the sea. 



The genus Etheria represents a small group of moUusks, 

 inhabiting the great rivers of Central Africa, having a shell 

 somewhat resembhng that of the Ostraaj though differing 

 essentially in being fluviatile, and in possessing two internal 

 muscles of attachment. 



When the genus was first established by Sowerby in his 

 ' Genera of Shells,^ he suspected it to be an inhabitant of 

 fresh water, in consequence of the shell being eroded, like 

 that of the Naiades, and the outer surface being often 

 covered with the remains of those ovate vesicular bodies 

 that adhere to the Neritina, and are supposed to be the 

 eggs of fresh-water mollusks. This conjectural opinion has 

 been singularly confirmed by recent discoveries ; the EthericB 

 having been found by Eang in the rivers of Senegal, and 

 by CailHaud in the Nile, as high as the cataracts of Eobatas, 



