ORTMANX: 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, wliich often goes down through a considerable amount of dry 

 soil, i)ut it is always iilled witli 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, l)ut 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. monongalensi.'i favors similar conditions, 

 3'et 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. movov(jaleiisl.^ 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 spi'ings collect to form a small swamp, this species is 

 found on its up])cr margin, not in the swamp. 



G. diogeiies does not haunt springs to the same extent as (.'. caroliims and ('. 

 monongalensl'i. 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 

 a swamp. It is also abundant in swampy ground along the borders of ditches and 

 streams, and in swamps formeil in depressions of the valleys of the large rivei-s 

 (abandoned o.x-bows). In the formerl}' glaciated area of the state it prefei-s kettle- 

 holes. Like C. monongalensvi it rarely occui*s in the .soft mud of swamps, but 

 generally along their borders, where the firmer ground affords a better ciiance 

 to dig more permanent holes. In consequence of the habit of preferring swamps to 

 springs, C. dioynies is generally found at a lower elevation than C. mmlinus 

 and monongalen-aiis, where it comes into contact with tlu'in. The two la.st named 

 forms occupy the region of the clear and cool spring-water, while ( '. dlugcius appi-ai-s 

 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. dingoics 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 fnsh and cKar spring-water 

 bubbling up. 



