270 MEMOIRS OF THE CARNEGIE MUSEUM. 



Distribution and Ecology (See fig. 27) : Type locality, Oak Orchard Creek, 

 Orleans Co., New York (Lea). 



This form apparently is a northern race of E. iris, and is found along the 

 northern edge of the range of the latter in the lake-drainage. Most of the localities 

 known are in the St. Lawrence-drainage in New York (Marshall, 1895, but quoted 

 generally as iris). It is known from the Erie Canal, in Onondaga Co., and from 

 Oneida Co., and by this route it may have crossed over into the Mohawk River 

 (Carnegie Museum). 



Our records show that it is in Lake Erie and some of its tributaries in Canada, 

 Pennsylvania, Ohio, and Michigan, and very likely the records from this region 

 given by Sterki (1907a) and Walker (1913) are to be referred to this variety. In 

 Michigan it is generally distributed, and since Walker (1898) calls it novi-eboraci 

 there is no doubt about it. 



Farther west its presence is doubtful. It occurs in Winona Lake (Wabash- 

 drainage !) , and Baker's figures make it probable that it is found also in the Chicago 

 area, but particulars are lacking. 



From Illinois the range certainly extends farther northwestward, as is shown 

 by our specimens from the drainage of the Red River of the North in North Dakota. 

 This localitj' is altogether new, for even the typical form has been only doubtfully 

 reported from Wisconsin, without exact locality, and has never been found beyond 

 this state. 



I found this variety only once in a creek (Conneaut Creek), and here it was 

 abundant in riffles in fine gravel and sand. In Lake Erie it lives in from one to two 

 feet of water on sandy bottom, and often among a scanty growth of rushes (Juncus 

 americanus) . 



Subgenus Eurynia Ortmann (1912). 

 Ortmann, 1912, p. 338."^ 



Type Unio recta Lamarck. 



Two species exist in Pennsylvania. 



Key to the Species of the Subgenus Eukynia. 

 «]. Shell of medium size, rather thin, more or less compressed, with a rather distinct, but rounded posterior 



ridge. Color of epidermis olive-green to olive-brown E. (E.) nasula. 



a 2. Shell large, thick, rather swollen, with the posterior ridge obliterated. Color of epidermis dark 



green to black, rarely brownish E. (E.) recta. 



"^ Simpson's (1914, p. 60) conception of the " subgenus " Eurynia differs entirely from ours. 



