500 NEW SPECIES OF UNIO. 



AVliile the males sustain a general resemblance to Unio clarJcia7ius,hG?i,, 

 and Unio gcrhardtii Lea, the emarginate character of the female form 

 is utterly unlike anything exhibited by the females of Lea's types. 



This form occurs abundantly in the same streams as the preceding, 

 outnumbering the other forms found combined. The specimens fig- 

 ured, while not the largest, are of average dimensions. Specimens of 

 both species may be seen in the Uuited States National Museum. 



Des Moines, Iowa, October 12, 1887. 



