I9I3-] ORTMANN— THE ALLEGHENIAN DIVIDE. 331 



G. symmetrica Hald. The former is common all over the Delaware, 

 Susquehanna, Potomac and James river drainages, and has been 

 found practically everywhere, possibly with the exception of the 

 smallest streams in the headwaters. This species has no closely 

 allied or representative form in the upper Ohio drainage, but if 

 Tryon's arrangement of the species (1866, p. 39 f.) is natural, re- 

 lated forms are found in Tennessee and Alabama. It is unknown 

 how far this species ranges southward, but according to our present 

 knowledge, it seems that it belongs rather to that group of fresh- 

 water forms, which point in their affinities to a center lying on the 

 southern Atlantic slope. 



Specimens of a Goniobasis collected by myself in Mason Creek, 

 Salem, and Tinker Creek, Roanoke, Roanoke Co., Va. (Roanoke 

 drainage) have been identified by Hinkleyas G. symmetrica, a species 

 reported (Tryon, '66, p. 30) from West Virginia, East Tennessee, 

 South Carolina, North Georgia, and Alabama. But there is much 

 uncertainty about this, and West Virginia seems to be more than 

 doubtful. One fact, however, is sure : this species is not found 

 north of the Roanoke on the Atlantic side. Thus also this appears 

 as a southern type, and should be classed with the same group as 

 G. virginica. 



In addition there is a species of Anculosa on the Atlantic side: 

 A. carinata (Brug.). This is absent in the Delaware drainage, but 

 extremely abundant in the systems of the Susquehanna, Potomac, 

 James, and Roanoke, and goes far up in the mountain streams. 

 This species is very closely allied to A. dilatata of New River and 

 the headwaters of the Monongahela, and undoubtedly stands in 

 closest genetic relationship to it. In fact, these two species are so 

 intimately allied on the one hand and are so polymorphous on the 

 other, that it is extremely hard to distinguish them. It has been 

 mentioned that they also have an allied but more sharply distin- 

 guished species in the upper Tennessee (A. gibbosa). 



There is no doubt that we have to class this case with those of 

 the very closely allied or identical species of Najades on either side 



less than twenty miles from Hot Springs, but only Anculosa carinata was 

 there, in various forms, some of which resemble very much Lea's figure of 

 G. nickliniana. 



