510 JSTUERIIDiE. 



of the left or attached valve. Muscular scars two, wide 

 apart, oblong, the anterior very long and irregular ; pallial 

 impression simple. 



Ex. iE.-seniilunata, Lamarck, pi. 120, fig. 3, 3, a. 



The visceral mass of the body in these auimals is pro- 

 traded backwards into the cavity of the mantle, and has 

 been described by M. Rang as the foot. There is, however, 

 uo distinct muscular foot in the adult animal, although, as 

 Dr. Gray observes, the foot may be present in the young 

 state before the shell is attached. Being adherent to each 

 other and to foreign bodies, a locomotive organ or foot would 

 indeed be superfluous to the animals, except in their young 

 state, when they are free. Of this genus, one species, 

 JEtheria Stefanensis, is met with in the river Amazon; 

 the others are from the great rivers of Africa, being found in 

 the river Senegal, and in the Nile above the cataracts ; these 

 latter are the " fresh-water oysters " mentioned by the tra- 

 veller Bruce, which are collected as articles of food by the 

 inhabitants, who also employ their iridescent valves in 

 ornamenting their tombs. 



Species of JEtheria. 



Cailliaudi, Ferus. semilunata, Lam. 



elliptica, Lam. Stefanensis, Moric. 



Genus MULLERIA, Ferussac. 



Shell in the adult state irrregular, inequivalve, covered 

 with a thick epidermis, and attached by the right valve ; 

 beaks elongated, gradually produced and thickened with age 

 in front of the fixed valve ; interior of the valves nacreous. 

 Ligament in a marginal groove. Adductor scars united, 



