THE ALLEGHENIAN DIVIDE, AND ITS INFLUENCE 

 UPON THE FRESHWATER FAUNA. 



(Plates XII-XIV.) 



ARNOLD E. ORTMANN, Ph.D., Sc.D. 

 (Read April 18, 19 13.) 



Contents : 



PAGE. 



Introduction ". 287 



Chapter 1: Statement of Distributional Facts in Najades 290 



Chapter 2: Systematic Affinities of the Najades of the Interior Basin and 



of the Atlantic Slope 3 2 3 



Chapter 3 : Distributional Facts in other Freshwater Animals 326 



Chapter 4: Summary of Distributional Facts which call for an Explana- 

 tion 338 



Chapter 5 : Physiographical Facts. History of the Allegheny Mountain 



Region 341 



Chapter 6 : Explanation of Distributional Facts 350 



Summary of Conclusions 381 



INTRODUCTION. 



It is a well-known fact, noticed already by Rafinesque, in 1820 

 (Monogr. Coqu. Biv. et Fluv.), that the Appalachian Mountain sys- 

 tem forms, for many freshwater animals, a sharp faunistic division 

 line, which separates a fauna known as that of the Interior Basin 

 from that of the Atlantic Slope (Mississippian and Atlantic Region 



PROC. AMER. PHIL. SOC. , LH. 2IO A, PRINTED JULY II, I9I3. 



Reprinted from Proceedings American Philosophical Society, Vol. Hi., IQ13. 



