ORTMAXN' : THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 449 



markedly in the eastern section of the state. This fact is significant, in so fai- as it 

 points out that the center of radiation for the state of Pennsylvania is rather on the 

 western side of the mountains than on tlie eastern (see Adams, 19M2, p. 122. "fnitrth 

 criterion for the detenu inat ion of centers of dispersaV). 



4. Canibarus hartoui robustus. 

 a. Siuiiiiiarij of Facts. (See pp. 390-391.) 



This form is found in Pennsylvania in a rather continuous area in the extreme 

 northwest, in McKean, Warren, Erie, and Crawford Counties, hoth in the Alleghany 

 River and the Lake l^rie drainages. It is often associated with the typical C. hartoui, 

 but has been found at different localities in Erie County without the latter. In 

 addition it is not rare in the northeastern part of Allegheny County in the Alle- 

 ghany River, and its tributaries, and has also been found in Chartiei-s Creek, in 

 southwestern Allegheny County. Here it is always associated with the typical form. 



In no other part of the state has this variety been discovered, and it is very im- 

 portant to note that no trace of it has been found in southwestern, central, southern, 

 and eastern Pennsylvania. Although C. hartoui is abundant in these parts, and 

 particular attention has been jjaid to the possible presence of C. hartoui rohnstus, 

 all attempts to find it have failed, and I feel justified in asserting that it is ab.sent here. 



I am not so sure of this with reference to the region lietween Crawford and ^^'arren 

 Counties on the one side, and Allegheny County on the other. 1 have searched in 

 this section for C. hartoni rohustiis, for instance near Tionesta, Forest County, at Oil 

 City, Venango County, in Mercer and northern and central Butler Counties, and near 

 Kittanning and Mosgrove, Armstrong County, l)Ut did not discover it. However, it 

 is possible that it is present along the course of the Alleghany River, in the river itself, 

 and some of its tributaries, in Forest, \'enango, and Armstrong Counties. In .some of 

 the places mentioned 1 did not strike streams which looked very favoralde, Ijcing gen- 

 erally not large enough. Yet in Erie and Crawford Counties I sometimes found this 

 species in rather small streams. Conditions in Otter Creek, Mercer County, Slip- 

 pery Rock (Jreek ami Tiioni (icek, Butler County, were apparently identical with 

 those under which it is generally found in Ij-ie County, but this form was not found. 



h. Origin of the distrihutioti <f C. hartoni robustus. 



Considering that the true C. barlotii roliu.'<tiis is a iiorthern form, being found 



outside of Pennsylvania in northern Ohio, western New York, and Canada (St. 



Lawrence Basin), its center of distril>ution .seems to be at tlie nortliwestern edge of 



the range of C hartoui, in the St. Lawreiuv drainage. In Peim.sylvania, however. 



