ORTMANN: monograph of the naiades of PENNSYLVANIA. 231 



that this is a bradytictic form, breeding from August to June. Surbcr's records also 

 confirm this (1912, p. 7): February, May, June, and August, September, October, 

 November, December. 



Remarks: A species easily recognized by the short-elliptical or ovate outline, 

 with the margins more regularly rounded (without angles) than in any other species, 

 by its oblique shape, with much anterior beaks, convex shell, and greenish-olive 

 color. The hinge-teeth are also quite peculiar. 



In the outline and convexity of the shell there is much variability, the posterior 

 end being more broadly or more narrowly rounded, and the beaks being more or 

 less anterior. In old shells the beaks are generally more anterior, sometimes 

 even being at the anterior end. The color also is somewhat variable, and old 

 shells are often discolored and dull brown, but not dark brown. In young shells 

 the pseudocardinals are somewhat divergent and not so distinctly parallel to the 

 laterals. 



Localities represented in the Carnegie Museum: 



Ohio River, Industry and Cooks Ferry, Beaver Co., Pennsylvania. 



Ohio River, Toronto, Jefferson Co., Ohio; St. Marys, Pleasants Co., West Virginia; Portland, Meigs Co., 



Ohio; Portsmouth, Scioto Co., Ohio. 

 West Fork White River, Riverside, Greene Co., Indiana (J. D. Haseman). 

 Tennessee River, Florence, Lauderdale Co., Alabama (H. H. Smith). 

 Mississippi River, Moline, Rock Island Co., Illinois (P. E. Nordgren). 

 Kansas River, Lawrence, Douglas Co., Kansas (R. L. Moodie). 

 Black River, Black Rock, Lawrence Co., Arkansas (H. E. Wheeler). 



Distribution and Ecology (See fig. 23) : Type locality, Kentucky River (Rafin- 

 esque) . 



One of the rarest species in Pennsylvania. It reaches the state only in the 

 Ohio River in Beaver and Allegheny Counties, and does not extend upstream 

 beyond Pittsburgh. 



Farther down the Ohio, it is found only in this river, and does not go into the 

 tributaries in the state of Ohio (Sterki, 1907a), but it is rather common here. It 

 has a wider distribution in Indiana and Illinois. In Indiana (Call, 1896a and 1900) 

 it is practically all over the state, and crosses over into the lake-drainage (Maumee) , 

 and goes even farther north into southern Michigan (Detroit, Grand, and Saginaw 

 Rivers, according to Walker, 1892, 1894, and 1898). It has been reported from 

 Lake Erie (Walker, 1913), and also from western New York, Niagara River and 

 Cayuga Lake (Marshall, 1895), and from the lower St. Lawrence in Canada (Ottawa, 

 Montreal, and Quebec, see Marshall, 1895; Bell, 1859; Whiteaves, 1863). How- 

 ever this northeastward expansion of the range is peculiar in its detail, and should 



