OKTMANN : THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 453 



by sucli minor barriei"s as an insignificant divide and a deepl}' eroded system of 

 valleys, renders it very probable tliat these obstructions are only temporary, and 

 may be overcome in time, and, on the other hand, that tlic immigration of tills 

 species is rather recent, its northward migration being not yet finished, but only 

 temporarily stopped. 



The fact that this species is restricted to a narrow strip within the mountains 

 is clearly due to its ecological habits. It prefers a certain altitude and clay bottoms. 

 'riic lattur are found in Pennsylvania chiefly on the Old Tertiary base-level, and this 

 is represented to a large degree only within the mountains. East of the Alleghany 

 Front and west of the Chestnut Ridge only insignificant renuiants of this base-level 

 are found, and thus this species is missing. 



AVe do not know anything about the Preglacial history of this species, and the 

 facts at hand furnish no evidence with regard to this question. According to the 

 mor{)hological characters, and compared with C. diogcncs and C. monoiKjahusis, we 

 must assume Preglacial age for it. Its immigration into Pennsylvania probably is 

 Postglacial, and thus it po.ssibly belongs to Adams' third wave of migration, starting 

 from the southeastern center (Adams, 1905, p. 62). However, in analogy to C. 

 monongalensis it may belong to the second wave, and the northeastern biota (see below 

 under C. monongalensis). 



6. Camhanis monongalensis. 

 a. Summari/ of FactJi. (See pp. 400-401.) 



Cambarrcs monongalcnisis occupies in Pennsylvania (.see PI. XLllI) a continuous 

 area in the southwestern part of the state. Toward the east, beginning at the south- 

 ern state-line, the limit of the distribution is formed by the Chestnut Ridge as far as 

 the point where the Loyalhanna River cuts through this ridge in Westmoreland 

 County. From this point the lioundary follows the Foyalhanna to the north, and 

 continues northwestward along the Kiskiminetas River. From the point where the 

 Kiskiminetas empties into the Alleghany, the latter river, ami further down the 

 r»hio, form the northern boundary of this species, until the Ohio leaves the state in 

 Reaver ( 'ount}'. 



Within this area this species has been found wherever it has been .searched for, 

 namely: ni (ireene, Washington, and southern Heaver Counties ; in the northwest- 

 ern section of P^'ayette County ; in the larger part of Westmoreland < "ounty. and in 

 southern .Mlegheny County. It has also been traced beyond the boundaries of the 

 state in a western and southern direction : it is found all over the Panhandle of 

 West Virginia (Hancock, I'rooke, Ohio, and Marshall ( 'ountii'sK and has also been 



