ORTMANN: monograph of the naiades of PENNSYLVANIA. 317 



branch. It is generally restricted to the main river, and only enters some of the 

 larger tributaries, for instance the Schuylkill, Juniata, and Chemung Rivers. 

 In the smaller tributaries it is absent, and the only specimen found by myself in 

 Conewago Creek, was in its lowermost part, which, during high water forms a 

 branch of the Susquehaima. 



Where found this species is generally abundant, even in smaller streams like 

 the Juniata in Huntingdon County, where it reaches its farthest advance in the 

 mountains. It is always found in lively currents, on shoals and riffles, in finer or 

 coarser gravel, and very often in bars of pure sand. Although it has been reported 

 from the tidewater region of the lower Delaware, it does not seem to be abundant 

 there (I did not find it near Fish House, Camden Co., New Jersey). 



In Pennsylvania its metropolis is apparently the Delaware from Trenton 

 upward, and the Susquehanna from the region of York Haven to the point where 

 the West and North branches unite. 



General distribution: Type locality, Delaware River, Philadelphia (Saj'). 



According to Simpson (1900) this species is found in the "Atlantic-drainage 

 from Georgia to the lower St. Lawrence," but this possibly requires some restric- 

 tion. Its occurrence in the lower St. Lawrence is extremely questionable, and 

 rests chiefly upon the statement of MarshaU (1895), who also gives it from Maine 

 (confirmed by Lermond, 1909, and Johnson, 1915). It is undoubtedly foimd in 

 Massachusetts and Connecticut (Gould-Binney, 1870, MarshaU, 1895, Linsley, 

 1848, Johnson, 1915). From New York it has been reported (Marshall, 1895) 

 from the Hudson-drainage up to, and even above, Albany, and there seems to be 

 even a western extension of the range through the Erie canal to Onondago and 

 Ontario Counties, but this should be investigated again, since it is not quite sure 

 that Marshall imderstood this species correctly. De Kay (1843) reports it from 

 the Passaic River, BelleviUe, Essex Co., New Jersey, and the species should exist 

 there: however, De Kay's figures represent, as has been said, L. ovata ventricosa. 

 Marshall (1895) gives it from the Raritan River, SomerviUe, Somerset Co., New 

 Jersey. Its distribution in Pennsylvania has been discussed above. From Dela- 

 ware it is known from Seaford, Sussex Co. (Rhoads, 1904). From the Potomac 

 River it has been reported from the District of Columbia and from the canal at 

 Alexandria, Fairfax Co., Virginia (Marshall, 1895), and it is found in Maryland 

 above Washington. However, it does not ascend far up in this river, and is surely 

 absent in the whole Potomac-drainage West of the Blue Ridge. 



To the South of the Potomac, records become verj^ scarce. Conrad (1836) 

 says that it is rare m the Potomac as weU as in the James River, and since Conrad 



