ORTMANN: THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 443 
established. Thus we see that in the beginning Genessee Lake was connected 
repeatedly with the upper Ohio (Alleghany River) drainage, but it is not probable 
that C. obscurus immigrated at this time, for then it ought also to have reached the 
Susquehanna drainage, since the lake discharged its water into the Susquehanna 
(through the “ Burns outlet”’) subsequently to the last connection (‘‘ Cuba outlet’’) 
with the Alleghany River. (See Fairchild, 1896, map, Pl. 19.) 
After this a discharge toward the upper Ohio was never re-established. But we 
know that stream-piracy has taken place in this region (headwaters of the Genessee), 
and although in some cases the Alleghany River seems to have captured parts of 
the Genessee drainage (Oil Creek has captured the head of Black Creek ; see Ley- 
erett, 1902, p. 207), the opposite has positively also taken place, for instance, Knight 
Creek and Van Campen Creek have captured, according to Fairchild, small lakes 
that once discharged towards Oswayo Creek, a tributary of the Alleghany. This may 
have happened after the sixth stage of Lake Genessee, when there was no longer 
any connection with the Susquehanna system, and would explain the presence of C. 
obscurus in the Genessee River and its absence in the Susquehanna. 
The eastern boundary of C. obscwrus in Pennsylvania is formed, generally speak- 
ing, by the divide between the Ohio drainage in the west and that of the Susque- 
hanna and the Potomac in the east. This is most evident in the northern part of 
this line, in Potter, McKean, Elk, Clearfield, Jefferson, and Indiana Counties. This 
species goes up the Alleghany River probably into Potter County, for it has been 
found not far away from the county line at Larabee, McKean County. It has not 
been found in the drainage of Clarion River in Elk and Jefferson Counties, but this 
is very likely due to the excessive pollution of this river. There is hardly a water- 
course known to me in Pennsylvania which is in a worse condition than Clarion 
River in Elk County. The wood-pulp mills at Johnsonburg, the tanneries at Ridg- 
way, the chemical factory at St. Mary’s discharge refuse into it, and Toby Creek 
adds sulphur water from the mines above Brockwayville (Jefferson County). Simi- 
lar conditions prevailin Red Bank and Sandy Lick Creeks in Jefferson County, but 
I have been able to ascertain the presence of this species near the head of Sandy 
Lick Creek at Dubois, Clearfield County (about 10 miles from the divide).* In 
southern Jefferson County, C. obscwrus is not present in Mahoning Creek at Punx- 
sutawney (although C. bartoni was there), this creek being slightly polluted by mine- 
waters; but I found it here in a pond connected with the creek. In Indiana 
County it is present in all creeks running to the Alleghany and Conemaugh (Little 
58] found this species here on June 16, 1905. Only two living specimens were taken, but numerous dead ones were 
lying in the creek. Apparently some injurious substance had been quite recently introduced into the water. 
