CONCHIFERA. 2?5 



CAST ALIA, Lamarck. 



Type, C. ambigua, PI. XVIII. fig. 4. Syn. Tetraplodon, Spix. 



Shell ventricose; trigonal; umbones prominent, farrowed; hinge-teeth 

 striated; anterior 2.1, short; posterior 1.2, elongated. 



Animal with mantle-lobes united behind, forming two distinct siphonal 

 orifices, the branchial cirrated. 



Distr. Rivers of S. America, Guiana, Brazil. 



