OKTMANN: THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 461 



it should liave Ijeen able to cross the latter. Consequentl}' its range extends 

 beyond tliat of C. mononyalensis. 



It is doulitful wliat physical feature constitutes the northern boundary of this 

 species. In Jefferson, Armstrong, and northern Butler Counties, where the boun- 

 dary is apparently located, the late Tertiary base-level, to which this species 

 belongs, loses its identity. Possibly it was not developed at all, and tliis region was 

 not reduced to base level. .So it might be possible that the roughness of the coun- 

 try constitutes a barriei' here, and this is supported l)y the fact that the boundary is 

 located further south in the .Mleghany vt-lle}' than to the east and west of it. On 

 the plateau-like regions in Indiana and Butler Counties, favorable localities are 

 abundant, while the narrow Alleghany valley, with tlie deeply cut valleys tributary 

 to it, do not offer congenial conditions. 



It is different further west. In Lawrence and Mercer Counties this .species has 

 invaded the glaciated area, and is found to the north of the terminal moraine 

 (see Lewis, 1884, p. 183 and 193, PI. 1 1 and 12), and here prefei-s the swampy depres- 

 sions formed by kettleholes. But a northern barrier at this point is not evident, 

 altliough a tendency to a northward extension seems to be indicated. 



Having thus invaded the area of the drift, it is not astonishing that this species 

 spread over large tracts of the latter in Ohio, Indiana, and Illinois. Its presence to 

 the south of the drift in the Mississippi Valley would then be a continuation of tins 

 westward migration, which finally varied toward the southwest and the south. 1 

 have represented it as such (Ortmann, 1905/;, p. 1 23, PI. 3) in a previous paper. Nev- 

 ertheless this question needs further investigation. 



There remains the eastern area of this species on the Atlantic Coa.-^tal Plain. In 

 the paper just referred to 1 have expressed the opinion (/. c, p. 123) that it ••de- 

 scended from the mountains" toward tbeea.st, but this apparently needs correction. 

 Of course the direct way from its supposed center to the Atlantic plain is from south- 

 western Pennsylvania and iioi-tliern Wi-st N'irginia across the .\ppalachian .-system 

 and the Piedmont Plateau to Maryland and \'irginia. I!ut the total ;d>sence of this 

 species from this region is against this assumption. Thoa"e is no possibU' reason whv 

 it should have disappearefl from the Potomac valley, if it had once been present 

 there, favorable localities being abundant. 



Comparing, however, the present eastern range of < '. <li();ifii(s \y\\\\ tiiat of ('. 

 liraoiius, we are struck at once by the general similarity. Hotli species lielong to 

 the ('oastal Plain from New Jensey southwanl, C illni/cueK g»)ing a little further 

 south, and not (juite .so far nortii, wliik- <'. limusit.t ha.s ent<?red the Piedmont 

 Plateau, and C. diogenci has not. This similarity induces us to assunu' a similar 



