ORTMANN: THE CRAWFISHESSOF THE STATE OF PENNSYLVANIA 463 
County, asmall part of the Atlantic Coastal Plain enters the state. The Delaware 
River runs along the escarpment of the Piedmont Plateau (‘fall line,’ See McGee, 
1888, p. 122), but at several places a narrow space is left, chiefly opposite Trenton, 
in Bucks County, and below Philadelphia, where alluvial flats are found. These 
we may include in the coastal plain, and they are characterized by the presence of 
C. diogenes (together with C. limosus). 
The next physiographical divisions of Pennsylvania are the Piedmont Plateaw 
and the Great Alleghany Valley, reaching from the eastern escarpment of the former 
to the Blue Mountain. These divisions form a unit in Pennsylvania. he divid- 
ing line between them, South Mountain, 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 haye here C. limosus, 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 instance, 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. Be 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 Alleghany 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, Cambarus 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 Bedford County ; 
and further, C. obscwrus exists in Wills Creek, Bedford County. Both these ex- 
See Willis, 1896, p. 172, and map p. 170-171. South Mountain is the continuation of the Blue Ridge of Vir- 
ginia, while the Blue Mountain of Pennsylvania is not identical with the Blue Ridge, but is to the west (northwest) 
of it. 
