ORTMANN: monograph of the naiades of PENNSYLVANIA. 



189 



Chemung River, South Waverly, Bradford Co., Pennsylvania. 



Tioughnioga River, Cortland, Cortland Co., New York (H. H. Smith) (drainage of upper North Branch 

 Susquehanna). 



Localities represented in the Philadelphia Academy of Natural Sciences: 



Juniata River, Tuscarora, Juniata Co. (S. N. Rhoads); Newton-Hamilton, Mifflin Co. (H. T. .Mather, 

 Jr.); Mount Union, Huntingdon Co., Pennsylvania (S. N. Rhoads). 



Distribution and Ecology (See figs. 18 & 19): Type locality, Susquehanna 

 River, Selinsgrove, Snyder Co., Pennsylvania. Ty/je set: Carnegie Museum Cat. 

 No. 61.4679. 



The above localities are all that are known, and they are restricted to the 

 Susquehanna-drainage in Pennsylvania and New York. The form goes up the 

 North Branch and its tributaries, reaching at least to Cortland, New York, and 

 down the Susquehanna as far as the vicinity of Harrisburg (Dimcannon). In 

 addition, it is found in Conodogtiinet Creek and the Juniata River. In the latter 

 it ascends rather far (Mt. Dallas, Bedford Co.). 



It should be noted, that it has not yet been found in the West Branch of the 

 Susquehanna; the few individuals at hand from the West Branch-drainage are 



Fig. 19. 

 + Alasmidonta marginata susquehannce. 

 • Alasmidonta varicosa. 



all A. varicosa. However, this section of the Susquehanna system is poorly knoA\Ti, 

 and most of it is badly polluted by mine-water and refuse from tanneries. Below 

 Harrisburg, in the part of the Susquehanna which traverses the Piedmont Plateau, 

 and in its tributaries in that region, this form has not been observed. 



The ecological habits of this variety are identical with those of the western 



