ORTMANN: TIIK CRAWFISHES OF THE STATE OF PENNSYLVANIA 415 



stream is inaiiitained ; after that it becomes scarce, but it does not disappear entirely, 

 and ill western Pennsylvania is frequently found associated with (\ ohsaini-^ in 

 eastern rcimsylvania with (!. limosns. In the large rivers it is generally entirely 

 absent, and, if louiid. it is at the inoutli of small streams, or at places where there are 

 springs on the banks. Here it becomes evident that temperature plays an impor- 

 tant part. The mountain streams, which are the favorite haunts of C. hartoni, are 

 characterized all the year round by a rather uniform, but comparatively low tem- 

 perature. Ill winter the temperature of the water goes down to just above the 

 freezing point, but generally remains slightly higher (in running water about 35°- 

 40° F.); in sunnner the ma.\imuin of these streams rarely goes above 60°, and does 

 so only temporarily for a few days, while in the larger streams it remains for weeks 

 above 70°, and may go up to H()° or even more. (The temperature of the Ohio 

 River at JJaden, Ik-aver County, on August 26, 1905, was 78° F. on a compara- 

 tivel}' cool day.) That it is tem[)erature which affects distribution is evident in 

 summer, when in western I'eniisylvania in the warm water of the rivers C obscums 

 is found, but where there are springs on the banks discharging perceptibly cooler 

 water into the river, C. hartoni suddenly appears. 



It may be mentioned that I once found this species under very peculiar condi- 

 tions. At New Hagerstown, Carroll County, Ohio, I discovered numerous burrows 

 in the black muck of a swampy meadow at the bottom of a small valley, which I 

 took first for burrows of C. diogeiies. But I was unable to get any diogaies, every 

 hole investigated being occupied l>v C. Ixirtoni (about half a dozen were taken). 

 This part of the meadow was clo.se to a hillside, at the foot of which were numerous 

 .springs with a lew stones, also sheltering specimens of ('. Inirtoui. < >n the other 

 side of the valley, which was al)out 100 to 200 feet wide, was a small stream with 

 sandy and gravelly bottom, and a few stones, where also a few C. hartoni were 

 present. The laigest number of specimens was present in the swampy meadow, 

 which is rather exceptional, but finds its explanation in the scarcity of stones in 

 this locality. 



The variety <'. hartoni rohiu^tus in general agrees with the typical form as con- 

 cerns ecological t-oiiditions, especially in tliat it prefers rough, rocky streams. How- 

 ever, it was found preferably in streams of a larger size, avoiding the smaller head- 

 waters. As Williamson (HXH.p. 11) puts it: "at the headwatei-s" (Sjuaw Run, 

 Allegheny County, is taken as an instance) "hartoni is found : following down the 

 stream roh n si u.'i is noticed; then an occasional ohscurun; till linally hartoni becomes 

 rare antl disappears; then rohudus disappears; and further down ('. oh.scurus is the 

 only species." 



