E T H E R I A. 



Genus ETHER lA, Lamarrk: 



Testa inaquivalvis, bimusculosa, irregularis, per valvam 

 inferiorem adhcerens, foliacea, frequenter vesicu- 

 laris, epidermide crasso, olivaceo induta ; intus mar- 

 garitacea. Margo cardincdis arcuato, edentulo, 

 foliaceo, valvcB inferioris plus minusve producto. 

 Ligamentum externum parlim in sulcum dispositmn, 

 partim super aream cardinalem ejcpansum. 

 Shell inequivalve, biinuscular, irregular, adliering by 

 the lower valve, foliacooiis, often vesicular, 

 covered with a thick olive epidermis ; pearly 

 within. Hinged margin arched, tootliless, folia- 

 ceous, that of the lower valve more or less pro- 

 duced. Ligament external, part placed in a 

 groove, part spread over the cardinal area. 

 It does not ajipear necessary to divide the numerous 

 forms of this genus into more tlian two species, namely 

 the Etheria eUiptica and Etheria Cailliaudi. They 

 occupy the large rivers of Africa : the former the Nile 

 and the Senegal, and the latter the Nile only, above 

 the Cataracts. Etheria Stephanensis, from the great 

 South American River Amazon, has been with great 

 propriety separated under the generic name Babte- 

 LETTIA. The Etherise may be simply designated 

 " Fresh-water Oysters," and some of the specimens 

 are not without beauty, arising from the pearly 

 structure of the interior, and (when unworn) the 

 striped wavings of the green epidermis. 



March. 



^p(•t;les 



(Mus. Brit.) 



Etiiehia elliptica. EiIi. festd solidiusculd, irregulari, 

 Iwvigatd, imirmatd; epidermide conrenirice strifjato ; 

 ared cardinali trigond, valvcB inferioris moderate 

 producto ; apicibus subdistantibus ; impressionibus 

 inuscularibus magnis, untied semilunari. 



The elliptical Ethehia. Shell rather solid, irregular, 

 smooth, unarmed ; epidermis concentrically striped, 

 cardinal area trigonal, that of the lower valve 

 moderately produced ; apices somewhat distant ; 

 muscular impressions large, the anterior one semi- 

 lunar. 



Lamap.ck. Anim. s. vert, tome 6. Etlicria, No. 1. 



Etheria semilunaris, Lamarck. 



Etheria trigonula, Lamarck. 



Etheria Carteroni, Michelin. 



Etheria Lamarckii, Ferrussac. 



Etheria plumbea, Ferrussac. 



Etheria transversa, Lamarck. 



Hob. The River Senegal and the River Nile. 



The above specific synonyms result from those 

 endless variations to which all attached shells of 

 foliaceous structure, whether marine or freshwater, 

 are liable. From the Lamarckian names we select the 

 first in numerical order. 



