ORTMANN: THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 417 
by them, and thus they are found at places where the groundwater is near the sur- 
face, in springs and swamps. In order to reach the water these species have to dig 
a hole in the ground, which often goes down through a considerable amount of dry 
soil, but it is always filled with water at the bottom. 
The three species belonging to this class differ slightly with regard to the selec- 
tion of their localities. C. carolinus chooses the mountains, and is found in springy 
places on the highest parts of the Alleghany plateau. The most favored localities 
are high valleys with a “hard pan,” that is to say a layer of stiff clay below, which 
serves to keep the groundwater within a few feet of the surface. In such places the 
surface is often apparently dry, but upon digging down fresh and clear spring-water 
is found at a depth of one to three feet, and the holes of this species go down to the 
‘hard pan” in order to reach the water. C. monongalensis favors similar conditions, 
yet it does not live in the mountains, but on the foothills west of the Chestnut 
Ridge. (The physiographic classification of these features will be discussed below). 
In this region extensive valleys with clay bottoms are rarely found, and thus 
C. monongalensis is content with the more restricted deposits of clay found on the 
hillsides. Such localities, however, are very abundant in this region, and wherever 
there is a spring and a certain amount of clay this species occurs. It prefers the 
cool spring-water, and if the springs collect to form a small swamp, this species is 
found on its upper margin, not 77 the swamp. 
C. diogenes does not haunt springs to the same extent as C. carolinus and C. 
monongalensis. It is sometimes found under similar conditions as the other two 
species, but generally at places where a spring or small stream spreads out to form 
aswamp. It is also abundant in swampy ground along the borders of ditches and 
streams, and in swamps formed in depressions of the valleys of the large rivers 
(abandoned ox-bows). In the formerly glaciated area of the state it prefers kettle- 
holes. Like C. monongalensis it rarely occurs in the soft mud of swamps, but 
generally along their borders, where the firmer ground affords a better chance 
to dig more permanent holes. In consequence of the habit of preferring swamps to 
springs, C. diogenes is generally found at a lower elevation than C. carolinus 
and monongalensis, where it comes into contact with them. The two last named 
forms occupy the region of the clear and cool spring-water, while C. diogenes appears 
a little further down stream, where the water is not so clear, and in summer 
not so cool. In and near swamps the water in the holes of C. diogenes is often 
stagnant and muddy (even sewage is not much objected to by this species), while 
in the holes of the other two species there is always fresh and clear spring-water 
bubbling up. 
