ORTMANN: monograph of the naiades of PENNSYLVANIA. 275 



water is subject to the tides. At Penn's Manor I found it in the deep water of a 

 protected cove, on a bottom consisting of mud and vegetable debris. The single 

 specimen from the Schu.vlkill Canal was in deep black muck, the only one found at 

 Yardley lived in gravel in an eddy in a riffle. 



In Lake Erie it is a very common species in Presque Isle Bay, where it is 

 present in all parts on sandy, gravelly, and muddy bottom, in from one to fifteen 

 feet of water, and it is also abundant in certain beach-pools of Presque Isle, on 

 sandy and sandy-muddy bottom. 



Sandy bottom of great, quiet bodies of water (tidewaters, lakes and probably 

 also canals) seem to furnish the conditions most favorable to this species. 



General distribution: Type locality, Schuylkill and Delaware Rivers, Phila- 

 delphia (SajO- 



The distribution of this species is unique: only Elliptio violaceus can be com- 

 pared with it, but even this is by no means identical (See under E. violaceus, p. 110, 

 and Walker, 1913). It is found on the Atlantic coastal plain, but does not go 

 far up into the rivers, at least in the southern part of its range. Although Simpson 

 (1900) reports it as far South as North Carohna, I have been able to find as its 

 most southern record only that of Conrad (1836) from James River, Virginia (the 

 figured specimen is from this place). Conrad also gives the Potomac river at 

 Washington, and this is confirmed by other writers (Dewey, 1856; Marshall, 

 1895) and by specimens in the Philadelphia Academy. It is not known from 

 anywhere in the headwaters of the Atlantic streams in Virginia and Maryland, 

 and I myself never found it in the upper James, the upper Rappahannock, and the 

 Potomac, on the Piedmont Plateau and W^est of the Blue Ridge. It has been 

 reported from the lowlands in Delaware (Rhoads, 1904). In Pennsylvania its 

 distribution is restricted chiefly to the lowlands, and it is absent in the upper 

 Susquehanna. In New Jersey it is known from the Delaware River and from the 

 coastal plain (Philadelphia Academy). I found it in the Delaware-Raritan Canal, 

 and in addition there is a locality (given above) in Sussex Co., northern New Jersey, 

 belonging to the upper Delaware-drainage, which is higlily interestmg. It is 

 found in New York in the Hudson River as far up as Troy and Albany (Aldrich, 

 1869; Marshall, 1895"^), and a number of localities are known from Connecticut, 

 Rhode Island, and Massachusetts (Linsley, 1845; Perkins, 1869; Carpenter, 1890; 

 Earle, 1835; Gould-Binney, 1870; Marshall, 1895; Johnson, 1915). It goes 

 northward to Keene, Cheshire Co., New Hampshire (Walker & Coolidge, 1908). 



From the Hudson-drainage in New York, this species ranges westward through 

 the Mohawk basin and the Erie canal, and enters the St. Lawi-ence-drainage. 



>" Marshall also gives Delaware River, but no exact locality. 



