Synoptical list of the families and genera noticed in the -present volume, torjether loith the 



respective type-sp)ecies. 



Sub-kingdom, 

 Class, 



MOLLUSCA. 

 PELECYPODA. 



• Shell resembling Cortif^o, thin, smooth, or concentrically striated, inequivalve, inequilateral; anterior side short, rounded, posterior produced, obliquely truncate, {raping; left 

 valve with a rid^e from the umlio to the postero-iuferior end. Hinge unknown. Type, l^t. Croncombtia, Jloore, from Ilhaetic beds at Beer-Croweonibe. Except by its thin structure, 

 this shell docs not appear to diller from Corbula. It is not stated which of the valves is the larger one, but the figure appears to indicate that the right valve is the larger one, which 

 is also usually the case in Corbula. 



d 



