ORTMANN: THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 447 



liowover, C. ohscurus has advanced north in the (Jenessee basin to a considerable 

 distance. 



3. ('ambarus hartoni. 



a. Sammar;/ of Fads. (See pp. 381-38G.) 



Cmahanis hartoni is very uniformly distributed all over the state, being, how- 

 ever, rather scarce in the extreme northwest in Erie ( 'ounty, where it is replaced 

 by the form C. bartani rohishis. 'We shall discuss this later. 



The species extends considerably beyond the limits of this state, chiefly toward 

 the southwest and northeast. In these directions it ranges from Tennessee and 

 North Carolina to New Brunswick and Quel)ec. Westward it reaches central Ken- 

 tucky and southern Indiana. The Atlantic Coastal Plain is apparently not invaded 

 by it to any considerable degree. 



We clearly see that its range follows the main strike of the Appalachian system, 

 and knowing that ecologically this species is a form of the rapid and cool waters 

 of the uplands and mountains, living preferably in small streams and even springs, 

 we understand that the distribution must be entirely different from what we have 

 learned with reference to the river-species already discussed. 



In Pennsylvania conditions seem to be favorable for this species everywhere, 

 possibly with the exception of a very narrow strip on the eastern border, along the 

 Delaware River (coastal plain); but even here it approaches the lowlands very 

 closely, the Piedmont Plateau reaching the river at many places. 



In the mountains elevation is no barrier for it, I found it mv-self at 2.G00 feet on 

 Laurel Hill Ridge, west of Jennerstown, and at 2,300 feet near Sandpatch, Somerset 

 County, and at other places at elevations not much less (Chestnut Ridge in West- 

 moreland County ; near Cresson. ( 'anibria ( ounty ; Keating Summit, Potter ( 'ounty). 

 At Davis, Tucker (bounty, WestMrginia, I collected it in Ijlackwater River at 3.050 

 feet, and Faxon, ISOS, p. (MD. records it from Roan Mountain, North Carolina, 



6,000 feet. 



b. Origin of the dintribiition of C. hartoni. 



The first point is to ascertain the center of radiation of this species. As I have 

 pointed out in a previous paper (1905, p. 121). we must regard the southern section 

 of the Appalachian system as the original home of the subgenus liartitniu.f. to which 

 this species belongs, and (/. c, p. 122) the advance and dispei-sal of the subgeiuis 

 took place over the eastern mountains of the T'nited States, the axis of the dispei^sal 

 being directed from southwest to northeast. 



We have reason to believe that the origin of this species falls into Preglacial 

 times, it being rather primitive within the subgenus (at least in comparison with the 



