70 



Bryant Wai^kEr 



delicate ; pseudo-cardinals rather compressed, high and ragged ; hinge plate 

 narrow; female shell very slightly swollen at the post-base. Marsupium 

 consisting of numerous, distinct ovisacs and having a well marked sulcus 

 extending around it at some distance above its base. 



Type: Unio cognatns Lea. 

 Example: P. elegans (Lea), fig. 196. 



Genus MEDIONIDUS Simpson, 1900. 



..sa 



Fig. 197 



Shell elongated, rather inflated, often arcuate when adult, sometimes 

 having a posterior ridge ; dorsal slope and occasionally the posterior portion 

 of the shell pHcately or nodulously wrinkled ; epidermis smooth and bright, 

 variagated with broken green rays and blotches; beak sculpture consisting 

 of rather fine, subparallel, often broken ridges in two loops, the anterior 

 rounded, the posterior somewhat angled, occasionally broken into zigzags; 

 pseudo-cardinals small, stumpy and somewhat roughened ; laterals rather 

 short, slightly curved and club-shaped; female shell shghtly swollen behind 

 the middle of the base. 'Marsupium occupying the central posterior part of 

 the outer gills, sometimes extending nearly their whole length. 



Type: Unio conradicus Lea, fig. 197. Animal, fig. 198. 

 Genus GLEBULA Conrad, 1853. 



Fig. 199 



Shell sohd, much inflated, short, elliptical, bluntly pointed and slightly 

 biangulate behind, with a low, posterior ridge ; female shell swollen at the 



