ORTMANN : THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 443 



establislied. Thus we see that in the beginning Genessee Lake was connected 

 repeatedly with the upper Ohio (Alleghany River) drainage, l)Ut it is not probable 

 that C. ohsciirus 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 coiniectiitn (" Cului outlet ") 

 will) the Alleghany Kiver. (See Fairchild, 1896, map. PI. 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 (headwatei-s of the Genessee), 

 and although in some cases the Alleghany River seems to have captured pails of 

 the Genessee drainage (Oil Creek has captured the head of Black ( 'reek ; see l^ev- 

 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 Genes.see, when there was no longer 

 an}' connection with the Susquehanna system, and would explain the presence of C 

 obf<ci(rn>> in the Genessee River and its absence in the Susquehanna. 



The eastern l)Oundar3'of C. obsairus in Pennsylvania is formed, generally speak- 

 ing, l)y the divide between the Ohio drainage in the west and that of the Susque- 

 luunui an<I the Potomac in the east. This is most evident in the northern part of 

 this line, in Potter, McKean, Elk, Clearfield, Jefferson, and Indiana ( 'ounties. This 

 species goes up the Alleghany River probably into Potter County, for it has been 

 found not far awa}' from the county line at Larabee, McKean County. It has not 

 been found in the drainage of Clarion River in Elk and Jefferson Counties, V>ut 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 ( 'larion 

 River in Elk County. The wood-pulp mills at Johnsonburg. the tanneries at Ridg- 

 way, the chemical fact(jry at St. Mary's discharge refuse into it, ami Toby ( 'reek 

 adds sulphur water from the mines above Brockwayville (Jefferson County). Simi- 

 lar conditions prevail in Red Bank and Sandy Lick Creeks in Jetlei-son ( 'ounty. 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, ('. ohscurus is not present in Mahoning Creek at Punx- 

 sutawney (although C. barUnii was there), this creek being slightly polluted by mine- 

 waters; but I found it here in a pond connectetl with tlu- creek, in Indiana 

 County it is present in all creeks running to the Alleghany and ( 'onemaugh ( Little 



"I found this species here on June IB. 190,5. Only two livinR specimens were taken, but nnnierous dead ones were 

 lying in the creek. Apparently some injurious substance had been quite recently introduced into the water. 



