PROCEEDI 



OF THE 



AMERICAN PHILOSOPHICAL SOCIETY 



HELD AT PHILADELPHIA 

 FOR PROMOTING USEFUL KNOWLEDGE 



Vol. LII May-August, 1913 No. 210 



THE ALLEGHENIAN DIVIDE, AND ITS INFLUENCE 

 UPON THE FRESHWATER FAUNA. 



(Plates XII-XIV.) 



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

 {Read April i8, 1913.) 



Contents : 



PAGE. 



Introduction 287 



Chapter i: Statement of Distributional Facts in Najades 290 



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



of the Atlantic Slope 323 



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 FIuv.), 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. 210 A, PRINTED JULY II, I9I3. 



