I9I3-] ORTMANN— THE ALLEGHENIAN DIVIDE. 339 



gahela it goes only up to a point at the lozver end of the canyon of 

 the mountain tributaries. This latter feature is expressed in the 

 Najades, and also in the genera Pleurocera and Goniobasis in the 

 Pleuroceridce. Also the crayfishes of the propinquus-group {Cam- 

 barus propinquus sanborni and C. obscurus) show it distinctly. 



(c) A third part is the region of the headwaters of the mountain 

 streams, tributary to Kanawha (New and Greenbrier) and Monon- 

 gahela (Buckhannon, Tygart, Cheat, Youghiogheny). This fauna 

 is chiefly characterized by 'negative features, by the absence of the 

 typical forms of the upper Ohio (2b). But it also has some positive 

 characters ; for instance, the presence of Symphynota tappaniana in 

 the upper Kanawha ; of Anculosa dilatata in the upper Kanawha, 

 Tygart, and Cheat ; and of Cambarus longuhts in the upper Kan- 

 awha. Of the various streams belonging to this region, each has 

 some features of its own, and the elements have various relations 

 to each other. It is very important to notice that most of the forms 

 found in these streams are represented, on the Atlantic side, by 

 identical or very closely allied forms {Symphynota tappaniana, 

 Strophitus edentulus, Anculosa dilatata, Cambarus longuhts) . Other 

 elements of this fauna belong to the general Ohio fauna {Symphy- 

 nota costata, Elliptio dilatatus, Alasmidonta marginata), and just 

 these have no closely allied forms on the Atlantic side {Alasmidonta 

 varicosa is indeed allied to A. marginata, but as we shall see, it is 

 not closely connected with the New River form). 



It further should be noted that the New River shows relations 

 to the upper Tennessee in Cambarus longidus, and possibly also in 

 Anculosa. Further, the upper Kiskiminetas-Conemaugh drainage 

 in Pennsylvania shows an intermediate condition between the more 

 southern mountain streams and the more northern tributaries of the 

 Allegheny; with regard to the Najades it conforms to the latter, 

 with regard to the crayfishes to the former (excepting again the 

 Loyalhanna). 



II. Eastern Side. 



1. The fauna of the Atlantic slope shows little evidence that it 

 ever was an important, independent center of radiation. All forms 

 belonging to it have more or less close relations to forms of the 



