ORTMANN: monograph of the naiades of PENNSYLVANIA. 217 



is chiefly found in the larger rivers (Ohio, White, Wabash, Kankakee, according to 

 CaU, 1896a & 1900). It is more abundant in Illinois (Baker, 190G; Forbes & 

 Richardson, 1913), and here it crosses over into the drainage of Lake jMichigan 

 (Calumet River, Baker, 1898a). It goes up the Mississippi in Illinois and Iowa, 

 and reaches Wisconsin in the Fox River (Barnes, 1823), and southern Minnesota 

 (Grant, 1886; Holzinger, 1888). 



Southward it is found in the western tributaries of the Mississippi in eastern 

 Kansas (Scammon, 1906), Arkansas (Call, 1895; Wheeler, 1918), Oklahoma and 

 Louisiana (Vaughan, 1893; Frierson, 1899) and also in eastern Texas (Singley, 

 1893). 



In the southern tributaries of the Ohio it has been reported from the Ken- 

 tucky River (Rafinesque). It is common in the Cumberland (Wilson & Clark, 

 1914) ; and, in the Tennessee, it ascends in the region of Knoxville into the lower 

 Clinch River (Carnegie Museum). 



It turns up in the Alabama-drainage (Lewis, 1870 and 1877; Call, 1885; 

 Carnegie Museum) , and there goes as far as the Etowah River in northern Georgia 

 (Call, 1885). 



In the north it has been reported in Michigan from the Grand and Saginaw 

 Rivers (Walker, 1894 & 1898), and it is also found in Lake Erie in Michigan and 

 Ohio (Sterki, 1907a, and W^alker, 1913). It has not been found in Pennsylvania, 

 and Call's record (1895, p. 12) from western New York has not been substantiated 

 by positive information. (It does not occur in the list of Marshall, 1895.) 



It is clear that the species has crossed over into the lake-drainage from the 

 upper Ohio system; but how it reached the Alabama-drainage remans to be 

 investigated. 



It is evident that it prefers large rivers, and it reaches Pennsylvania only 

 in the large streams. According to my observations, it is found chiefly in the 

 deep channel of the Ohio, upon the shell-banks, and is regularly taken by the 

 clam-diggers. Scammon (1906) gives gravel-beds as the favorite habitat. But 

 it seems to be also found on muddy bottoms (Baker, 1898a), and CaU (1900) says, 

 that it is almost ubiquitous with regard to its habitat. In Pocatalico River I 

 found it in pm"e, shifting sand. 



Genus Cyprogenia Agassiz (1852). 

 Ortmann, 1912, p. 212; Simpson, 1914, p. 326. 



Type Obovaria stegaria Rafinesque. 

 Only one species known from Pennsylvania. 



