CONCHIFERA OR BIVALVES. 105 



masses. They are so firmly attached that it is 

 difficult to avoid breaking the shell when they 

 are removed from rocks. 



65. Etheria. — Shell inequivalve, very irre- 

 gular ; teeth none ; bosses short and indistinct ; 



ligament external, penetrating partly into the 

 shell. Animal, foot large. — 5 species recent. 



This genus is found in the rivers of Africa 

 and Madagascar, and is abundant in the Nile 

 above the Cataracts, where the inhabitants col- 

 lect them for the purposes of ornamenting their 

 tombs with the shells, and feeding upon the 

 animal. They are pearly within, foliaceous on 

 the outside, large, and fix themselves by the 

 under valve often to one another, presenting 

 the most curious distortions of form. The in- 



