ORTMANN: THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 427 
Similar conditions seem to have played a part in the distribution of this species 
in the Potomac River. It has been reported from an old canal (Chesapeake and 
Ohio) four miles south of Cumberland, and I have found it in the Potomac at 
Cherry Run, West Virginia, and at South Cumberland. At both places it was scarce, 
and I am much inclined to believe that in this region (western Maryland and east- 
ern West Virginia) it got into the river from the canal. Originally its distribution 
in Maryland was very likely similar to that in Pennsylvania, belonging only to the 
Coastal Plain and the Piedmont Plateau.” 
Of the tributaries of the Potomac in southern Pennsylvania those which empty 
into the Potomac east of the Alleghany Mountain region also possess this species. 
It has been found in the drainage of the Monocacy River at Gettysburg, Adams 
County, and that of the Conococheague Creek in Franklin County, the latter local- 
ity again belonging to the Great Alleghany Valley. Further west, within the Alle- 
ghany Mountains, it seems to be absent. I did not find it in Big Cove Creek and 
Tonoloway Creek, Fulton County, and it is not in the collections made by Mr. H. 
A. Pilsbry for the Philadelphia Academy in Sideling and Town Creeks, Washington 
and Alleghany Counties, Maryland. This supports the view that the presence of 
this species in the Potomac as far up as Cumberland is due to the existence of the 
canal. Above Cumberland, where the canal ends, C. limosus is positively absent in 
the Potomac drainage in Pennsylvania as well asin Maryland and in West Virginia. 
Thus it seems that C. limosus belongs originally only to the larger rivers of the 
southeastern section of our state, and that its real center for Pennsylvania is the 
Delaware. It has spread, however, upstream, and has approached the Alleghany 
Mountain region, even entering the latter in the Susquehanna River. ‘This upstream 
dispersal is apparently not everywhere due to natural migration, but has been 
favored in recent times by canals. The present northwestern boundary, disregard- 
ing the Susquehanna River, is marked by a line (see Pl. XLIII) running from New 
Hope, Bucks County, to Maiden Creek and Reading, Berks County, thence to Bain- 
bridge, Lancaster County, Carlisle, Cumberland County, and to Williamson, Frank- 
lin County. This line, generally speaking, runs parallel to the Blue Mountain, and 
it is very likely that the differences in the physical features of the Piedmont Plateau 
and the Alleghany Mountains have something to do with the distribution of this 
species, although the real cause cannot any longer be clearly seen, the original con- 
ditions being apparently obscured by several factors. For it should not be forgotten 
that the streams from the Susquehanna to the Delaware, issuing through the Blue 
“The Chesapeake and Ohio Canal forms a continuous waterway from Washington to Cumberland, and was com- 
pleted in 1850, see Hulbert, 1904, p. 160, and map opposite p. 80. 
