ORTMANN : THE CRAWFISHES OF THE STATE’ OF PENNSYLVANIA 44] 
of the Susquehanna. If transport were at all probable we should expect to find 
that it had taken place here, as well as in the region of Lake Erie. 
Further, and this is the most important objection to the transport theory, while 
C. obscurus has invaded the Lake drainage, not only in Pennsylvania, but also in 
New York (Genessee River), in no case has the opposite taken place namely, that 
C. propinquus has invaded the Ohio drainage. If the crossing of the divide were 
due to passive transport, the same cause should have acted in both directions; but 
C. propinquus is entirely absent from the Ohio system. 
The latter objection holds good also with reference to another assumption, that 
C. obscurus may have crossed into the lake drainage by the aid of the old canal 
which connected the Beaver River with Lake Erie (Erie extension of Beaver canal). 
This canal (see Jenkins, 1903, p. 288, 289) was in part used as early as 1834, and 
was completed in 1844; it was abandoned in 1871, and it cannot be denied that by 
it C. obscwrus might have been able to reach the Erie drainage. I would not hesi- 
tate to accept this as correct if it were not for the fact that C. propinquus has not gone 
in the opposite direction. Precisely in the region of this old canal my collections 
are very complete, and are supplemented by those of others (Messrs. O. E. Jennings, 
D. C. Hughes, and W. R. McConnell), so that I am positive about the absence of 
C. propinquus. 
On the other hand, we have seen that the specimens of C. obscwrus from the 
tributaries of the lake seem to approach more closely those of Beaver River than 
those of French Creek. This would be in favor of the canal-theory, the canal run- 
ning from Newcastle by the way of Shenango River to Conneaut Creek (Jenkins, 
/. c.), While French Creek was not so closely connected with it (although there was 
a “French Creek feeder”). The absence of C. propinquus in the Beaver drainage 
may be due to the fact that in Erie County, the canal was not so closely connected 
with the streams running to the lake, and that thus the lake species could not get 
into the canal; or else C. propinquus being the weaker species of the two could not 
make any headway against the more vigorous C. obscwrus. 
There remains another theory, namely, that the migration of C. obscwrus into 
Conneaut and Elk Creeks is due to stream-piracy. The latter has undoubtedly 
taken place in this region in Postglacial times. The Postglacial divide between 
Lake Erie and the Ohio was formed originally by moraines of the late Wisconsin 
stage (Lake escarpment morainic system. See Leverett, 1902, Pl. 18; also Carll, 
1880, Pl. 1) or by higher elevated parts of the non-morainic drift lying immediately 
5a Tt should, however, be borne in mind that the discharge of the water from the canal was downward toward the 
lake and thus that migration might in that direction have been easier than in the opposite. — EpITor. 
