220 MEMOIRS OF THE CARNEGIE MUSEUM. 



tributaries. Thus, for instance, it occurs in Ohio, in the Muskingum at Marietta 

 (Hildreth, 1828), in the Tuscarawas (Dean, 1890; Sterki, 1907a), and in the 

 Scioto and Great Miami (Sterki). Sterki reports it also from the Mahoning 

 River, but it has never been found in the Pennsylvanian part of it, and never 

 anywhere else in the Beaver-drainage. In Indiana it is found besides the Ohio, in 

 the White and Wabash Rivers (Call, 1896a and 1900). In Illinois it occurs only 

 in the Wabash (Baker, 1906). A number of localities are known in Kentucky, 

 Tennessee, and northern Alabama in the Cumberland and Tennessee systems 

 (See Wilson & Clark, 1914). 



West of the Mississippi it has been reported only by CaU (1895) from the St. 

 Francis River, Wittsburg, Cross Co., and Saline River, Benton, Saline Co., Ar- 

 kansas, but this is questioned by Simpson, and correctly, as I think. I know that 

 this species is represented in this region (Missouri, Kansas, Arkansas, Oklahoma) 

 by another, C. aberti (Conrad), which has apparently been mistaken for the one 

 under consideration. 



In the Ohio between Pittsburgh and Cincmnati this species is found in the 

 mussel-beds in the deep channel of the river, on gravelly bottoms with steady 

 currents. In the Tennessee-drainage I found it frequently in firmly packed gravel, 

 in strong!}' flowing water, in rivers of medium size (Clinch, Holston). 



Genus Obovaria Rafinesque (1820).^*^ 

 Ortmann, 1912, p. 320; Simpson, 1914, p. 289. 



Type Unto retusa Lamarck. 

 The genus is divided into two subgenera. 



Key to the Subgenera, of Obovaria. \ 



at. Shell rounded or subovate, upright, vnth nearly central, or anteriorly incurved beaks. Pseudo- 

 cardinals divergent, not parallel to the laterals. Epidermis more or less brown. Nacre often red 



or purplish Subgenus Obovaria. 



02. Shell ovate or eUiptical, oblique; beaks quite anterior. Pseudocardinals in adult specimens sub- 

 parallel to the laterals. Epidermis greenish. Nacre white Subgenus Pseudoon. 



Subgenus Obovaria Simpson (1900). 

 Ortmann, 1912, p. 321; Simpson, 1914, p. 290. 



Type Obovaria (Unio) retusa Lamarck. 

 Two species and one variety are found in Pennsylvania. 



Key to the Forms of Obovaria. 

 Oi. Shell as high as, or higher than, long. Beaks much elevated and much incurved. Nacre deep purple 

 with white margin 0. retusa. 



^^ Not " 1819," as Simpson gives the date. In 1819 Rafinesque published this name, but as " uomen 

 nudum." 



