OUTMANN: THE CRAWFISHES OF THE STATE OF PENNSYf-VANIA 467 



I 



congenial conditions in the lake. The specimens taken may have been accidentally 

 swept into the lake. Thus I do not believe that it will be discovered in the part of 

 the lake bordering upon Pennsylvania. 



C. immunis, however, besides being found in northern Ohio, reappears in New 

 York. Faxon (1898, p. 654) has recorded it from a tributary of Oneida Lake, and 

 recently 1 have seen specimens, belonging to the New York State Museum, col- 

 lected by Mr. V. (\ Paulmier in Rens.selaer Lake, Rens.selaer County. Thus its 

 presence in New York, upon which I cast some doubt ( 1905/>, p. 134), is to be 

 regarded as firmly established. However, the connection of these eastern localities 

 with the western range has not been discovered. If a connection is present at all, it 

 is to be looked for in the Erie-St. Lawrence basin, and thus would possibly include 

 the lake shores of Pennsylvania. Yet this connection may not exist, and C. immiinh 

 in New York may be a recent, artificial introduction, which is not altogether impos- 

 sible, since we know that the crawfishes used for food in the New York market come 

 in part from the lake regions (Milwaukee, see Ortmann, 1900, p. 1260), and thus 

 this species may have been introduced. But this question is by no means settled, 

 and we should try to obtain further facts. 



Finally we may observe that the conditions now existing in the case of the 

 Pennsylvania!! crawfishes may not be original, but may have been altered by human 

 agency. The possible influence of canals upon the dispersion of two species. C. 

 limosus in the east, and C. obscuru.s in ( 'rawford and Erie Counties, has been dis- 

 cussed in the foregoing pages, and the transplantation of C. uhscuru.s into Wills 

 Creek has been stated to liave apparently occurred, accidently or intentionall}', 

 tlirough human agen(;y. No other ca.ses of dispersion beyond the natural bountlaries 

 l)y artificial means are probable. Put on the other hand certain species may have 

 become extinct, at le;istin parts of their original range, through human agency. Of 

 this we have man}' instances, but in our state none has gone so far as to entirely 

 obscure the original conditions. \\'l' have pointed out above that the absence of C. 

 limosKs in the Delaware and Schuylkill Rivei-s in the region of the (ireat Alleghany 

 Valley may be due to the pollution of the streams issuing from the anthracite region. 

 That these rivers, as well as the Susquehanna are considerably polluted partly by 

 city sewage, partly by mine-water, is sure (see Leighton, 190:3. p. 112, and 1904. 

 p. 48), but whether the absence of C limmois in this region is due to this fact, or not, 

 cannot be settled. 



It is dilFerent in the western part of the state. Here C. o/wcv/r«.v originally occu- 

 piril all of the Monongahela and .Mlcghanv drainages west of the Chestnut Kidge, 

 but tin re are many streams in which it is now lacking, and in which we must assume 



