jEtiieriid.e. 509 



Ex. C. cordata, Humphrey, pi. 120, fig. 2, 2, a. 



The three undisputed species we have given, are from the 

 rivers of South America ; many others have been described, 

 but are only considered varieties. 



Species of Castalia. 



cordata, Humph. nodulosa, Wood. 



Duprei, Recluz. 



Fain. ^THEEIIDiE. 



Animal with the body large, thick, oblong, projecting 

 backwards into the mantle-cavity. Labial palps very large, 

 semi-oval, attached by the straight side, without any free 

 points. Mantle-lobes bearded, disunited in their entire 

 length ; gills two on each side, unequal, dependent, united 

 behind and to the body and mantle. Foot none. 



Shell, when young, regular and free ; when adult, irregular, 

 attached by the surface of one valve ; valves covered with a 

 thick, olivaceous epidermis, pearly within. Hinge without 

 teeth ; ligament sub-internal. Muscular scars two, the 

 anterior small and linear (united in the adult state in 

 Mulleria). 



Fluviatile. 



Genus .ETHERIA, Lamarck. 



Shell irregular, inequivalve, adherent by the beak and by 

 tubular prolongations of one of the valves; surface of 

 valves foliaceous, covered with a thick, olivaceous epi- 

 dermis ; pearly within, the nacre vesicular or appearing as 

 if blistered. Hinge-margin curved, toothless ; ligament 

 external, tortuous, partially sunk in a groove of the area 



vol. ir. 3 u 



