100 MEMOIRS OF THE CARNEGIE MUSEUM. 



Cahaha Kivcr, (jurnee, Shelbj' Co., Alabama (H. H. Smitli). ' 



Distribution and Ecology in Pennsylvania (See fig. 10) : In the Ohio and Lake- 

 drainage of western Pennsylvania this is, next to Strophitus edentulus, the most 

 abundant species. It is practically ubiquitous, and there are few streams, which 

 contain any shells, in which it has not been found. It is moreover common in 

 the large rivers as well as in small creeks, and in some of the latter it is the leading 

 form. 



This wide and universal distribution undoubtedly is due to the fact, that 

 this species is not very particular with regard to its station, and it is hardly possible 

 to say that it prefers any definite ecological conditions. It is found in riffles in 

 small streams, as well as among heavy rocks in the larger rivers; it is upon the 

 shell-banks of the Ohio, as well as in quiet pools and eddies with muddy bottom; 

 it is in lakes upon sandy, gravelly, and muddy bottoms. Nevertheless the uni- 

 formity of its characters is quite remarkable, and even beyond the limits of Penn- 

 sylvania there is hardly any change. 



General distribution: Type locality, not specifically given by Rafinesque, but 

 Vanatta gives "Kentucky River." 



According to Simpson (1900), this species has the following range: "Entire 

 Mississippi-drainage; St. Lawrence and its tributaries; Alabama River system; 

 southeast into Florida; southwest to Guadeloupe River, Texas." However, this 

 includes several varieties. 



Typical E. dilatatus is certainly found in western New York, occurs in the 

 Kanawha system up to the Bluestone River in West Virginia, and in New River 

 to Virginia (See Call, 1885, and Carnegie Museum). In the Tennessee it extends 

 to northern Alabama, and in the headwaters to southwestern Virginia. North- 

 ward it is found in Canada, Michigan, Wisconsin, and Minnesota. Westward it 

 extends to Iowa, Kansas, Oklahoma, and northern Louisiana. In the Alabama 

 system and in southern Arkansas it is largely represented by the form snbgibbosus 

 (Lea) (See Lewis, 1877). But some specimens from the Cahaba, Black Warrior, 

 and Tombigbee-drainages in the Carnegie Museum, represent the typical phase, 

 while specimens from the Coosa are all subgibbosxis. Likewise in Arkansas the 

 two forms seem to pass into each other (See Wheeler, 1918). 



E. dilatatus passes over into the drainage of Lake Michigan and Lake Erie, 

 but, as we shall see below, in Lake Erie proper, it assumes a peculiar form, which 

 is entitled to subspecific rank. In the tributaries of the lake, the typical form is 

 always present. 



In western New York, it has been reported from the St. Lawrence-drainage as 



