ORTMANN: monograph of the naiades of PENNSYLVANIA. 249 



Soft parts (See Ortmann, 1912, p. 331). Glochidia (See Lefcvre & Curtis, 

 1910, p. 97, fig. K, and 1912, p. 146, fig. K; Ortmann, 19116, PI. 89, fig. 19; Coker 

 & Surber, 1911, PI. 1, fig. 2; Surber, 1912, PI. 2, fig. 28). My measurements are: 

 0.08 X 0.09; those of Lefevre & Curtis: 0.07 X 0.09; those of Surber: 0.070 X 

 0.095 mm. 



Breeding season: I have the following records for gravid females: Aug. 30, 

 1909 (beginning to have eggs); Sept. 8, 1908; Sept. 10, 1908; Sept. 11, 1913; 

 Sept. 17, 1913; Sept. 22, 1910; Sept. 25, 1908; Oct. 5, 1909. Then again in 

 spring: May 9, 1913; May 19, 1911; May 22, 1909; May 24, 1911; May 25, 

 1914; July 7, 1910; July 8, 1910; July 11, 1909. This is a bradytictic form, the 

 breeding season beginning in September. A specimen partly charged with eggs 

 was found as early as August 30. Toward the end of September glochidia are 

 found, but eggs have been observed as late as October 5. In spring, in May, 

 glochidia are present, and discharge has been observed on May 22 (in Lake Erie). 

 In the beginning of July the same has been found to be the case, and the latest 

 date for a discharging female, Julj^ 11, refers to a specimen from the Ohio River. 

 Thus part of July and August should be regarded as the "interim." There does 

 not seem to be any difference between Lake Erie and the Ohio-drainage. 



Surber found glochidia in October, November, January, June, July, and 

 August, and thus it appears that under certain conditions the seasons may overlap 

 in August. 



Remarks: A species easily recognized by its subovate, compressed shape and 

 high posterior wing, and, if the latter is reduced, by its yellowish color, thin shell, 

 generally pink nacre, and weak or imperfect hinge-teeth. With regard to the 

 development of the wings there is great variability. Young specimens generally 

 have a well-developed, elevated, posterior wing, and a small anterior wing. But 

 in old specimens the wings may become lower, and are sometimes absent (in manj'' 

 cases evidently broken off). This is chiefly true of specimens from the rivers 

 (Ohio), while the shells from Lake Erie preserve the wings better, even in large 

 individuals. This is undoubtedly due to the enviromnent. The outline of the 

 shell varies greatly with the absence or presence of the wings being more regularly 

 elliptical, or subovate, or even subtriangular. There is also great variability m the 

 hinge, the pseudocardinals being sometimes distinct, sometimes very poorly 

 developed, knob-like, or like low ridges. 



Contrary to what has been noted in other cases, the form from Lake Erie is 

 larger and finer than the Ohio form. This is undoubtedly due to the fact, that the 

 river-environment, as developed in western Pennsylvania, is not favorable to this 



