498 The American Naturalist. [June, 



U. luteolus Lamarck. 



This almost universally distributed species, is not without its 

 representation in the rivers of Illinois. 

 U. tuberculatum Barnes. 



" Very common and fine ; growing to a length of six and a 

 half to seven inches. A characteristic species, totally unlike 

 any other Unio. Found in many parts of the United States, 

 and in all waters and localities maintaining its distinct in- 

 dividuality. In northern waters, nacre white. In the far 

 south a few specimens are found in which it is purple. 

 U. alatus Say. 



Not numerous, but found sparingly all along the river. One 

 was found two years ago, nine inches long. 

 U. lasvissimus Lea. 



Very plentiful and fine ; a beautiful glossy epidermis and 

 purple nacre. 

 U. gracilis Barnes. 



Quite common in certain localities ; grows quite large, but 

 the older shells show much erosion and are apt to be indented 

 or otherwise injured. This Unio and the two preceding it, are 

 a family group, and present many characteristics in common. 



, but a few fine large ones are found, always pre- 

 senting the peculiar liver colored nacre of this species. The 

 young ones I have not yet met with. Have received this shell 

 from Iowa under the name of U. graniferus Lea. 

 LI pustulosis Lea. 



One of the most numerous of all the unios found in Illinois. 

 In Spoon river all sizes from the small young shells to the 

 largest adults are easily found. 

 U.pustulotus Lea. 



Not so common as the preceding but distinguished from it 

 by the lesser number and larger size of the pustule. 

 U. lacrymosus Lea. Synonym asperrimus Lea. 



Plentiful, and beautifully marked ; does not grow so large 

 in Spoon river, as in the rivers of Indiana; some shells 



