ORTMANN: THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 457 
becomes rather probable. This is in keeping with the morphological characters, as 
compared with C. diogenes, for the latter, as we shall see below, is very likely also 
preglacial. 
We have no evidence as to the Preglacial history of ©. monongalensis. It may, 
however, be said, that it must have come from the original home of the subgenus 
Bartonius in the southern Appalachians. How far north it extended in Preglacial 
times we do not know, but the advancing ice cannot have driven it back very far. 
This is very probable because it is a form decidedly partial to cold water. With 
reference to its Glacial-Postglacial migration it belongs to the northeastern biota and 
the second wave of Adams; but its advance was apparently checked at an early date 
by the Ohio-Allegheny River. 
It will be remembered that with reference to C. carolimus another view has been 
expressed (p. 453). In the case of that species we do not possess any facts which 
enable us to fix its time of immigration into Pennsylvania with the same proba- 
bility as in the case of C. monongalensis. ‘The present extension of the range of C. 
carolinus in the southern mountains classes it rather with the southeastern biota. On 
the other hand, we know nothing about the southern range of C. monongalensis, and 
thus it is at present impossible to properly compare these two species. Their close 
affinity, however, and the identity of the ecological conditions under which they 
are found (aside from the difference in altitude) render it rather probable that the 
parallelism observed between them in some respects may reveal itself also in others. 
7. Cambarus diogenes. 
a. Summary of facts. (See pp. 405-407.) 
Aside from a narrow strip along the Delaware River, in Delaware, Philadelphia, 
and Bucks Counties in eastern Pennsylvania, this species covers a large area in 
southwestern Pennsylvania, namely all the region occupied by C. monongalensis, 
and, in addition, a belt of a certain width to the north of it (see Pl. XLIII). Here 
the eastern boundary is formed, as in the case of C. monongalensis, by the Chestnut 
Ridge, but it is continued beyond the Loyalhanna River, extending into Indiana 
County, and then it follows the divide between the Susquehanna and Allegheny 
drainages as far north as the southern extremity of Jefferson County. From this 
region the boundary runs in a westerly direction. 
In Jefferson County I found this species at Punxsutawney, and I have seen 
chimneys rather abundantly to the east of this place, when riding on the Buffalo, 
Rochester, and Pittsburgh Railroad, about as far as Big Run, Jefferson County. But 
