ORTMANN: THE CRAWFISHES OF THE STATE OF PENNSYLVANIA © 415 
stream is maintained ; after that it becomes scarce, but it does not disappear entirely, 
and in western Pennsylvania is frequently found associated with (. obscurus, in 
eastern Pennsylvania with C. /imosws. In the large rivers it is generally entirely 
absent, and, if found, it is at the mouth 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. bartoni, are 
characterized all the year round by a rather uniform, but comparatively low tem- 
perature. In 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 summer the maximum 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 80° or even more. (The temperature of the Ohio 
river at Baden, Beaver County, on August 26, 1905, was 78° F. on a compara- 
tively cool day.) That it is temperature which affects distribution is evident in 
summer, when in western Pennsylvania in the warm water of the rivers C. obscwrus 
is found, but where there are springs on the banks discharging perceptibly cooler 
water into the river, C. barton 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. diogenes. But I was unable to get any diogenes, every 
hole investigated being occupied by C. bartoni (about half a dozen were taken). 
This part of the meadow was close to a hillside, at the foot of which were numerous 
springs with a few stones, also sheltering specimens of C. bartoni. On the other 
side of the valley, which was about 1U0 to 200 feet wide, was a small stream with 
sandy and gravelly bottom, and a few stones, where also a few C. bartoni were 
present. The largest 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 C. barton’ robustus in general agrees with the typical form as con- 
cerns ecological conditions, especially in that it prefers rough, rocky streams.* How- 
ever, it was found preferably in streams of a larger size, avoiding the smaller head- 
’ 
waters. As Williamson (1901, p. 11) puts it: ‘cat the headwaters” (Squaw Run, 
Allegheny County, is taken as an instance) “ bartoni is found ; following down the 
stream robustus is noticed ; then an occasional obscwrus; till finally bartoni becomes 
rare and disappears; then robustus disappears; and further down C. obscurus is the 
only species.” 
