ORTMANN: THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 459 
Plain, not even entering the Piedmont Plateau. The western range begins in 
southwestern Pennsylvania and northern West Virginia, and we have seen that it 
here belongs chiefly to the late Tertiary base-level of the rivers. But in Pennsyl- 
vania it has entered the glaciated area (Lawrence and Mercer Counties), and thence 
has spread westward over the states of Ohio, southern Michigan, Indiana, Illinois, 
Wisconsin, southern Minnesota, and Iowa. Its main range is here in the glaciated 
region. But it also occupies localities south of the drift, in Indiana, Kentucky, 
Illinois, Missouri, Kansas, Arkansas, Mississippi, and Louisiana, extending westward 
to Colorado. 
b. Origin of the distribution of C. diogenes. 
The first point to be ascertained is whether there is actual discontinuity between 
the eastern and western range of this species. In western Pennsylvania I have 
positively located an eastern boundary for this species. It is formed by the divide 
between the Susquehanna and the Alleghany in the north, further south by the 
Chestnut Ridge. In the northern parts of West Virginia I am also positive that it 
is not found east of the Chestnut Ridge in Preston and Tucker Counties. We have 
the report of Faxon (1885a, p. 71) that this species is found at Deer Park, in western 
Maryland, but, as we have seen, this is erroneous (p. 406, footnote 27), and the species 
is absent in this whole region. [| have searched for it in vain in Somerset and 
Fayette Counties (east of the Chestnut Ridge) in Pennsylvania, in Preston, Tucker, 
and Mineral Counties, West Virginia, and in Garrett and Alleghany Counties, Mary- 
land. Hast of the Alleghany Front, in the Alleghany Mountain region, in the 
Great Alleghany Valley, and the Piedmont Plateau it is positively absent. It has 
never been recorded from anywhere within these physiographical divisions, and I 
myself made special search for it in Bedford, Blair, Fulton, and Franklin Counties, 
and in the eastern section of Pennsylvania, and further in the Potomac valley at 
Cumberland and Hancock, Maryland, and Cherry Run, West Virginia. At many 
of these places highly favorable localities were discovered, but no chimney-builders 
were found. ‘This is the more convincing since I succeeded with ease in demon- 
strating the presence of this species on the alluvial flats of the Delaware River in 
Pennsylvania. 
Although our knowledge of the distribution of C. diogenes in Virginia and North 
Carolina is far from being complete, all known localities are on the Coastal Plain, 
and thus it appears that there is actually a gap in the distribution formed physio- 
graphically by the Appalachian system and the Piedmont Plateau. 
Our knowledge of the distribution in the west is also very defective, and more 
particularly we do not know anything about its southern boundary in West Virginia 
