ORTMANN: monograph of the naiades of PENNSYLVANIA. 45 



The sexual differences are sometimes quite striking, but not always so. It 

 is by no means "one of the easiest species in which to distinguish the sexes," as 

 Scammon (1906, p. 314) says. In the largest specimen, mentioned above, I am 

 in fact in doubt whether it is a male or a female, and it is true that sometimes m 

 large males (determined by the soft parts), the posterior end of the shell is some- 

 what expanded, with less developed ribs. But, as a rule, in individuals of medium 

 and large size, the sex may be easily told from the shape of the shell. In young 

 shells this is very hard, or even impossible to do. 



It should be mentioned that the fem.ale shell is on the average more flattened 

 and compressed than that of the male. This also is a rather unusual feature. 



Localities in Pennsylvania, represented in the Carnegie Museum: 



Ohio River, Industry, Beaver Co. 



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



Mahoning River, Mahoningtown, Coverts, and Edinburg, Lawrence Co. 



Shenango River, Harbor Bridge and Pulaski, Lawrence Co.; Sharpsville, Mercer Co. 



Pymatuiiing Creek, Pymatuning Township, Mercer Co. 



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



Dunkard Creek, Wiley and Mount Morris, Greene Co. 



Allegheny River, Kelly, Armstrong Co. 



Locality in Pennsylvania, represented in the Philadelphia Academy of Natural 

 Sciences: 



Ohio River, Coraopolis, Allegheny Co. (S. N. Rhoads). 



Other localities represented in the Carnegie Museum: 



Ohio-drainage: 

 Tuscarawas River, Ohio (Holland collection). 

 Wolfe Creek, Washington Co., Ohio (W. F. Graham). 

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

 West Fork River, Lynch Mines, Harrison Co.; West Milford, Harrison Co. (W. F. Graham); Lightburn, 



Lewis Co., West Virginia. 

 Little Kanawha River, Bui-nsville, Bra.xton Co., West Virginia. 

 Pocatalico River, Raymond City, Putnam Co., West Virginia. 

 Elk River, Sutton and Gassaway, Braxton Co., West Virginia. 

 New River, Hinton, Summers Co., West Virginia. 

 Levisa Fork Big Sandy River, Prestonsburg, Floyd Co., Kentucky. 

 Licking River, Farmer, Rowan Co., Kentucky. 



Tennessee-drainage: 

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

 Shoals Creek, Lauderdale Co., Alabama (H. H. Smith); Elk River, Fayctteville, Lincoln Co., Tenncs-^^ee 



(H. H. Smith); Hurricane Creek, Gurley, Madison Co., Alabama (H. E. Wheeler); Paint Rock 



River, Trenton and Princeton, Jackson Co., Alabama (H. H. Smith); Bear Creek, Burleson, 



Franklin Co., .Alabama (H. H. Smith). 



