296 MEMOIRS OF THE CARNEGIE MUSEUM. 



in the tidewaters of the Delaware. According to the older records, its metropolis 

 seems to be in the lower Delaware near Philadelphia. It ascends the larger rivers 

 (Delaware and Schuylkill), but the upper boundary has not been ascertained. 



In the Susquehanna-drainage it is distinctly a rare shell. It has been found 

 in the lower part (York Haven, Pilsbry) , but otherwise it is restricted to its larger 

 branches. In the West Branch it has been traced up to WiUiamsport, in the 

 North Branch to the New York state line."^ 



Although present in the lower Potomac, it has never been found in the drainage 

 of this river in Pennsylvania, and it seems to be absent in the whole upper Potomac 

 system West of the Blue Ridge Mountain. 



Having found this species only at a few places, and probably not in the most 

 favorable environment, I am unable to say what are the ecological conditions, 

 which it prefers. In the Delaware above Trenton and in the Susquehanna I found 

 it in strongly flowing water in gravel. But here it was unquestionably rare. 

 If its metropolis is in the lower parts of the large rivers, it might be a tidewater 

 species, prefering quiet water, and sandy or muddy bottom. At any rate, I found 

 it on sandy bottom in the lake-like part of the Delaware at Fish House, New 

 Jersey. 



General distribution: Type locality, Given by Gmelin from Malabar, which, 

 of course, is incorrect. Lamarck (1819) reports it from Saratoga Lake in New 

 York, and if there should not be any other earlier record, we might select this as 

 the type localitj'. Simpson (1914) gives Virginia as type locality. 



This species belongs to the Atlantic-drainage from Virginia to Maine. In 

 Virginia it is chiefly present according to Conrad (1836) in the tidewaters,^^'' and 

 farther South it assumes a different shape, and has been called conspicua. Its 

 presence in the lower Potomac in Virginia and the District of Columbia is well 

 estabhshed (Dewey, 1856; Marshall, 1895). It is knowTi from the state of Delaware 

 (Rhoads, 1904), Pennsylvania, New Jersey (lower Delaware River, and Second 

 River, Belleville, Essex Co., as ochrace%s De Kay, 1843), from New York, Con- 

 necticut, Rhode Island, Massachusetts and Maine (See Linsley, 1845; Perkins, 

 1869; Gould-Binney, 1870; Carpenter, 1890; Lermond, 1909; Johnson, 1915). 

 In New York (Marshall, 1895) it ascends th6 Atlantic rivers (Upper Susquehanna 

 and Hudson) reaching the Mohawk, and crossing over into the St. Lawrence- 

 drainage, where it is found in Lake Ontario and its tributaries, and down the 



'^^ It goes farther up in New York state, since it occurs in Little Lakes and Schuyler's Lake in the 

 region of the headwaters, and has been reported from Chenango and Tioga Rivers. 



''° It is positively absent in the mountains west of the Blue Ridge, and also seems to be absent or 

 rare on the Piedmont Plateau. 



