ORTMANN: THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 413 
conditions. In the mountain streams the rocks are rolled over very frequently, not 
only at high stages of water, but also under ordinary conditions, and this apparently 
does not suit the tastes of this species, and may be even directly dangerous. Since 
the general direction of the migration of this species in western Pennsylvania was 
and is upstream, it is evident that falls and rapids in the mountain regions present 
effective barriers, In the ponds and lakes of western Pennsylvania, connected with 
the Ohio drainage, this species is very abundant, but here also it always selects 
stones under which to hide. 
Cambarus propinquus is restricted to Lake Erie and the lake drainage. It lives 
in the tributaries of the lake, exactly under the same conditions as C. obscwrws. In 
the lake itself it has been found on two occasions. Dr. D. A. Atkinson collected a 
number at Presque Isle in the bay, but particulars as to their habitat were not 
recorded. The only other specimen from the lake was collected by myself on the 
sandy and gravelly beach near Miles Grove, thrown out by the surf, but alive. It 
does not seem to be very abundant in the lake, or at any rate seems to favor 
only certain places, and we may presume that places with stones and rocks on 
the beach and not too much exposed to the surf are the proper localities in which 
to look for it. 
Cambarus propinquus sanborni in Ohio and West Virginia is found under exactly 
the same ecological conditions as its representative forms in Pennsylvania. 
Nothing was known hitherto as to the ecological habits of C. obscwrus and pro- 
pinquus, except the short notice of Hay (1896, p. 498), that in Indiana C. propin- 
quus lives “in the smaller streams hiding under stones, concealed in short burrows 
along the banks, or resting quietly on the bottom.” 
2. The Mountain Stream Species: Cambarus bartont. 
Conspicuously differing from “the River Species,” Cambarus bartoni favors the 
rough streams of the mountains, hills, and the uplands generally, and is absent from 
the large rivers. The size of the stream may vary. In fact it goes up to the very 
sources and is found in the springs. ‘The amount of water may be very small. In- 
deed it is frequently found in streams which dry out superficially during the hot 
season. But in such cases water is always present at a certain depth. The varying 
and often scanty supply of water forces this species to accommodate itself to these 
conditions, and thus it has become to a certain extent a burrowing species. It 
always selects stones to hide under, and in larger streams with a permanent supply 
of water is satisfied to scoop out a hollow under the stone after the fashion of C. 
obscurus. But very often the burrows are more complex, consisting of a hole going 
