ORTMANN: monograph of the naiades of PENNSYLVANIA. 



175 



mistakable aspect of an Alasmidunta. If attention is paid to the tiinge, there can 

 be no mistaking this shell, for the teeth are unique, at least among Pennsylvanian 

 shells. 



There are no species related to this in western Pennsylvania, and this species 

 has altogether a rather isolated position in the system (See Ortmann, 1913a, pp. 

 324, 361). 



Localities represented in the Carnegie Museum: 



Delaware River, Shawnee, Monroe Co., Pennsylvania. 



Princess Creek, Kunkletown, Monroe Co., Pennsylvania. 



Schuylkill Canal, Manayunk, Philadelphia Co., Pennsylvania. 



Marsh Run, three miles S. E. of Remington, Fauquier Co., Virginia (Rappahannock-drainage). 



Mountain Run, Culpeper, Culpeper Co., Virginia (Rappahannock-drainage). 



Locality represented in the Philadelphia Academy of Natural Sciences: 



Big Neshaminy Creek, " Edderton," '-'' Bucks Co., Pennsylvania (H. W. Fowler). 



Distribution and Ecology (See fig. 17) : Type locality, SchuylkiU River, Penn- 

 sylvania (Lea). 



In Pennsylvania this species is decidedly rare. I have found it in large numbers 

 only in the Schuylkill Canal; at other localities only a few were obtained. It is 



Fig. 17. 



+ Alasmidonta heterodon. 



• Alasmidonla undulata. 



known from a number of localities in the Delaware-drainage in the vicinity of 

 Philadelphia, and chiefly from streams on the Piedmont Plateau. But in the 



'" Probably = Eddingtou. 



