82 Bryant Wai^ker 



Subgenus DYSNOMIA Agassiz, 1852. 



Shell of the male with a posterior and central radiating ridge, with a 

 wide flattened space between, that of the female with a greatly produced 



Fig. 220 



inflation a little behind the centre of the base, being a continuation of the 

 central ridge. 



Type : Unio foliatns Hild., fig. 220. 



Subgenus PILEA Simpson, 1900. 



Fig. 221 



Male shell with a wide, shallow, radiating depression in front cJf the 

 posterior ridge, that of the female with a rounded foliaceous swelling at 

 the posterior base. 



