ORTMANN: monograph of the naiades of PENNSYLVANIA. 225 



Soft parts (See Ortmann, 1912, p. 323). Glochidia identical with tliose of var. 

 levigata, 0.20 X 0.23 mm., while Surber (1915, p. 7, fig. 8) gives: 0.170 X 0.215 mm. 



Breeding season: I fomid the typical suhrotunda gravid with glochidia on 

 Sept. 22, 1910, and gravid and discharging on May 25, 1911. A female with eggs 

 was found on Sept. 6, 1914. Surber gives June 9, 1913 for glochidia. This would 

 agree with the bradytictic character of the species. A single individual, however, 

 discharging glochidia, was received from A. A. Hinkley, collected on Aug. 9, 1912 

 in the Wabash River. Probably this specimen was exceptionally belated. 



Remarks: The more or less circular outline and subglobular shape, the almost 

 central beaks, and the light color of the posterior slope, serve to distinguish this 

 species. But there is great variability in the outline, and also in the convexity of 

 the valves, and, according to the latter, a variety (levigata) must be distinguished 

 from the main species, which will be treated below, and it should be pointed out, 

 that the latter is closely connected with the normal form by intergrades. 



Another "species," distinguished by Lea (and Simpson), 0. leibi (Lea), is 

 nothing but the form from Lake Erie of 0. subroturida. It differs merely in its 

 smaller size (largest at hand: L. 42, H. 38, D. 26 mm.), and has, like many lake- 

 forms, more regular and more distinct growth-rests. It is also sometimes lighter 

 in color. I shall not treat of it here in detail, since I have not yet found it on the 

 Pennsylvanian shores of the lake. 



Localities in Pennsylvania represented in the Carnegie Museum: 



Ohio River, Neville Island, Allegheny Co. 



Monongahela River, C'harleroi, Washington Co. (G. A. Ehrmann). 



Beaver River, Wampum, Lawrence Co. (G. H. Clapp & H. H. Smith). 



Other localities represented in the Carnegie Museum: 



Oliio River, St. Marys, Pleasants Co., West Virginia; Parkersburg, Wood Co., West Virginia; Portland, 



Meigs Co., Ohio. 

 Wabash River, New Harmony, Posey Co., Indiana (A. A. Hinkley). 

 West Fork Wliite River, Riverside, Greene Co., Indiana (J. D. Hasemau). 

 Little Kanawha River, Grantsville, Calhoun Co., West Virginia (W. F. Graham). 

 Elk River, Shelton and Clay, Clay Co.; Gassaway and Sutton, Braxton Co., West Virginia. 

 Holston River, Mascot, Kno.x Co., Tennessee. 



Distribution and Ecology (See fig. 23): Type locality, Ohio River (Rafinesque). 

 (Vanatta says: "Kentucky River".) 



In Pennsylvania the typical 0. subrotnnda is restricted to the Ohio, the Beaver, 

 and the lower Monongahela, and it should be kept in mind, that just in this region 

 more compressed specimens turn up, which establish the transition toward the 



