76 



Bryant Walker 

 Genus CARUNCULINA Simpson, 1898. 



Shell small, inflated, obovate, rather solid, with a thick dark epidermis, 

 which is rayless or only feebly rayed; beak sculpture consisting of rather 

 strong, concentric ridges, which form, as a general thing, only a single 

 rounded loop in front and are strongly curved upward behind. Pseudo- 



Fisf. 208 



Fig. 209 



cardinals compressed, smooth on the inside, generally reflected upward, 

 somewhat torn on the edges. Shell quite commonly pointed posteriorly, that 

 of the female truncated obliquely on the post-base. Marsupium kidney- 

 shaped, formed by a few large ovisacs, projecting beyond the gill; female 

 having a well developed caruncle on the inner edge of the mantle in front 

 of the branchial opening. 



Type : Unio parvus Bar., fig. 208. Animal, fig. 209. 



Genus EURYNIA Rafinesque, 1820. 



Shell oval to oblong; surface smooth; beak sculpture delicate, double- 

 looped; female shell more or less expanded or swollen in the post-basal re- 

 gion. 



Inner edge of the mantle in the female distinctly papillate. Marsupium 

 kidney-shaped, ocupying the posterior part of the outer gill. 



Key to the subgenera of Eurynia. 



Shell elongate, more or less pointed behind. 



Papillae on inner edge of mantle regular, uniform, reaching to 



middle of lower margin Bnrynia s. s. 



Shell subovate or subelliptical, not much pointed behind. 

 Papillse on inner edge of mantle irregular, not reaching to mid- 

 dle of lower margin Micromya. 



