OKTMANN : THE CKAWFISHES OF THE STATE OK PENNSYLVANIA 463 



County, a small part of the At/antic Coastal Plaiv enters the state. 'J'lie Delaware 

 River runs along tlie escarpment of the I'iedmont Plateau ("f;\ll line," See McGee, 

 1888, p. 122), hut at several places a narnnv space is left, chiefly opposite Trenton, 

 in Bucks County, and helow Philadelphia, where alluvial Hats are found. These 

 we may include in the coastal plain, and they are characterized h\' the presence of 

 C. dioyenes (together with C. limos-iis). 



The next physiographic-al divisions of Pennsylvania are the Piedmont Plateau 

 and the Great Alhghainj I'allci/, reaching from the eastern escarpment of the former 

 to the Blue Mountain. These divisions form a unit in Pennsylvania. The divid- 

 ing line between them, South jNIountain, being rather insignificant and obliterated, 

 chiefly toward the northeast."'"' This fact is also expressed to a certain degree in 

 the distribution of the crawfishes. Aside from the generally distributed C. bartoni, 

 we have here C. limoaus, which has invaded this region, coming from the lower 

 Delaware, Susquehanna, and Potomac. It seems to have spread all over the Pied- 

 mont Plateau, and also into parts of the Great Alleghany Valley, for in.stance, into 

 the Cumberland Valley (between South Mountain and the Blue Mountain, called 

 here the North Mountain, in Franklin and Cumberland Counties). It has also 

 been found in the Schuylkill and its tributaries in Berks County, but not as yet in 

 the Lebanon and Lehigh Valleys (northeastern continuations of the Great Alleghany 

 Valley). Whether the conditions presented here are original or not seems doubtful. 

 On the one hand it may be that the canals have served to distribute this species ; 

 on the other hand, pollution of streams may have restricted it. IV this as it 

 may, the fact remains that the physiographical divisions distinguished as the Pied- 

 mont Plateau and the Great Alleghany Valley possess a species of crawfish which 

 is not found elsewhere, except in the Coastal Plain and the Susquehanna Valley. 



Then follows the Alleghani/ Mountain region, between the Blue Mountain and 

 the Alleghany Front (see Willis, 1. c). In the southern and central parts of the 

 state this section is well marked. In the northern part its western boundary is 

 obliterated, the Alleghany Front losing its identity. But all the areas which 

 undoubtedly belong to the mountain region are uniformly characterized by the 

 presence of only the one species, Cambarvs bartoni, with the exception that C. 

 limosus is found in the middle Susquehanna valley from Harrisburg upward to 

 Columbia and Center Counties, and in the Juniata valley up to Ik-dford County ; 

 and further, C. ofc.scun/.s- exists in Wills ("reek, Bedford ('ounty. I'oth these ex- 



"See Willis, 1896, p. 172, and map p. 170-171. Soutli Monntnin is the continuation of the Blue Kiilgc of \ ir- 

 (;inia, while the Blue Mountain of Peiinsylvania is not identical with the Blue Kid(;r, but is to the we»t (northwest) 

 of it. 



