ORTMANN: monograph of the naiades of PENNSYLVANIA. 93 



Breeding season: Gravid females have been found only once by myself, on 

 June 22, 1909 (with eggs and young glochidia). Surber secured them on July 14, 

 1911. Thus the duration of the breeding season remains uncertain, but probably 

 is short, and ends in July. 



Remarks: A verj' characteristic species, which cannot be confused with any 

 other form. In fact Rafinesque's definition of U. nigra as a "large, heavy shell, 



Fig. 10. 



■ Elliptiu niger. 



D do. do. (Indian garbage heap.) 



• Elliptio dilatatus. 

 + Elliptio dilatatus sterkii. 



with red nacre, from the Ohio," is entirely satisfactory. The shell varies greatly 

 in shape, and may be shorter or longer in proportion to height, but is always recog- 

 nized by its subovate outline, the distinct posterior ridge, and the color of the 

 nacre. The peculiar sculpture of the posterior slope is well-developed only in 

 young shells. 



Localities in Pennsylvania represented in the Carnegie Museum: 



Ohio River, Smiths Ferry (W. F. Graham), Shippingjiort, Cooks Ferry, Inchistry, and Beaver, Beaver 

 Co.; Shoustown (R. Fcerster), Coraopolis (S. N. Rhoads), and Neville Island, Allegheny Co. 



Allegheny River, Harmarville and Natrona, Allegheny Co.; Braeburn, Westmoreland Co.; Aladdin, 

 Godfrey, Johnetta, Kelly, and Templeton, Armstrong Co. 



Monongahela River, Charleroi, Washington Co. (G. A. Ehrmann). 



