ORTMANN : THE CRAWFISHES OF THE STATE OF PENNSVLVAXIA 459 



Plain, not even entering the Piedmont Plateau. The western range begins in 

 southwestern Pennsylvania and northern West Mrginia, and we have seen that it 

 here belongs chiefly to the late Tertiary base-level of the rivers. l>ut 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, 

 Wiscon.sin, southern Minnesota, and Iowa. Its main range is here in tlie glaciated 

 region. But it also occupies localities south of tiie drift, in Indiana, Kentucky, 

 Illinois, Missouri. Kansns. Arkansas. Mississippi, and Louisiana, extending westward 

 to Colorado. 



b. Origin of the distribution of C. diogeiies. 



The first point to be ascertained is whether there is actual discontinuity between 

 the eastern and western range of tliis species. In western Penn.sylvania I have 

 positive!}' located an eastern boundary for this species. It is formed by tiie divide 

 between the Susquehanna and the Alleghany in the north, further south by the 

 Chestnut Ridge. In the northern parts of ^^'est \'irginia I am also positive that it 

 is not found east of the Chestnut Kidge in Preston and Tucker Countie.*. We have 

 the report of Faxon (1885«, 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 tliis whole region. 1 have searched for it in vain in Somei-set and 

 Fayette Counties (east of the Chestnut Ridge) in Pennsylvania, in Preston, Tucker, 

 and jMineral Counties, West Virginia, and in Garrett and Alleghany (.'ounties, Mary- 

 land. East of the Alleghany Front, in the Alleghany Mountain region, in the 

 Great Alleghany ^'alley, and the Piedmont Plateau it is positively absent. It has 

 never been recorded from anywhere within these physiograj)hical 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 favoiablo localities were discovered, but no chimney-buildere 

 were found. This is the more convincing since 1 succeeded with ease in demon- 

 strating the presence of this species on the alhivial flats of the Delaware River in 

 Pennsylvania. 



Although our knowledge of the distribution of ' '. '//(»/*/«>• in \'irginia 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 pliysio- 

 graphically by the Appalachian system and the Piedmont Plateau. 



Our knowledge of the distribution in tlie west is also very defective, and more 

 particularly we do not know anytliing about its southern boundary in West \'irginia 



