ORTMANN: monograph of the naiades of PENNSYLVANIA. 109 



Barton Run, bcluw Tomlisons Mill (= Jeiiningt; ^lill), ^larlton, Burlington Co., New Jersey (C. H. 



Conner)."" 



Poto m ac-(Ira inage : 

 Potomac River, Cabin John, JNIontgomery Co., Maryland (J. D. Ilascman); Hancock, Washington Co., 



JNIaryland; Cherry Run, Morgan Co., West ^'irginia. 

 Wills Creek, EUerslie, Allegheny Co., Maryland. 



South Branch Potomac River, Southbranch and Romney, Hampshire Co., West Virginia. 

 Shenandoah River, Harpers Ferry, Jefferson Co., W'est Virginia. 

 North Fork Shenandoah River, Broadway, Rockingham Co., Virginia. 

 South Fork Shenandoah River, Elkton, Rockingham Co., Virginia. 

 South River,Waynesboro, Augusta Co., Virginia. 



Soxithcrn localities: 

 Rappahannock River and jNIarsh Run, Remington, Fauquier Co., Virginia. 

 IMountain Run, ('ulpei)cr, Culpeper Co., Virginia. 

 Rapidan River, Rapidan, Culjicper Co., Virginia. 

 North River, Lexington, Rockbridge Co., Virginia. 

 Calf Pasture River, Goshen, Rockbridge Co., Virginia. 

 Jackson River, Covington, Allegheny Co., Virginia. 

 Roanoke River, Salem, Roanoke Co., Virginia. 

 Tinker Creek, Roanoke, Roanoke Co., ^'irginia. 

 Mason Creek, Salem, Roanoke Co., Virginia. 



Distribution and Ecology in Pennsylvania (See fig. 11): This i.s the commonest 

 form of Naiades in the Atlantic-drainage in Penns3'lvania, and is as characteristic 

 and as abundant on the eastern side of the Alleghenian divide, as is E. dilaiatus 

 on the western, in fact, it is even more universally distributed than the latter. 

 (Ortmann, 1913a, pp. 361, 362). It apparently has no ecological preferences, 

 being found practically in any permanent body of water; in canals and reservoirs 

 with quiet water and muddy bottom, as well as in large rivers with strong current 

 and heavy gravel and rocks. In the small creeks it goes up very far into the head- 

 waters, and is found, for instance, in the small tributaries of the West Branch of 

 the Susquehanna, close to the divide as in Cush Cushion Creek in Indiana County. 

 Here it is only about twenty miles away from the nearest locality of E. dilatatus 

 in the Allegheny-drainage in Indiana County. (Yellow and Little JMahoning 

 Creeks.) Also in Mrginia, similar observations have been made (See Ortmann, 

 1913a). In the region, where the headwaters of New River and those of the 

 James and Roanoke Rivers come together, the two species are found immediately' 

 west and east of the divide. 



The abiUty of E. violaceus to live everywhere under a great variet}^ of environ- 

 mental conditions undoubtedly' accounts for its great variability, as well as its 



'" Qui,te a peculiar form, unusuallj" swollen, with white nacre, which requires further investigation. 



