HARRIS : CRAYFISHES GENUS CAMBARUS. 89 



least as far back as the burrows were found, had been covered 

 with water. The burrows near the stream were less than six 

 inches in depth, and there was a gradual increase in depth as 

 the distance from the stream became greater. The holes farther 

 from the stream were in nearly every case covered by a mound 

 which, when they were far distant from the stream, was hard 

 and dry, while those nearer had only a very small chimney, or 

 none at all, and subsequent visits proved that at that time of 

 the year the mounds were just being constructed. In the deeper 

 holes, some of which reached a depth of three feet, he invariably 

 found at various points enlargements which, he considers, rep- 

 resent the end of the burrow at some earlier period, the burrow 

 being undoubtedly projected deeper as the water falls in the 

 ground, for all burrows went down to water. 



"The burrows near the stream were seldom more than six 

 inches deep, being nearly perpendicular, with an enlargement 

 at the base, and always with at least one oblique opening." 



Tarr's description of the burrows corresponds well with that 

 given by Girard. He also gives a diagram of a section of a 

 typical burrow. "Occasionally the burrows are very tortuous, 

 and there are often two or three extra openings, each sometimes 

 covered by a mound." The burrows have a diameter of one 

 and one-half to two inches, are smooth and of almost uniform 

 diameter for the entire length. 



Of the chimneys he says : "There is every conceivable shape 

 and size in the chimneys, ranging from a mere ridge of mud, 

 evidently the first foundation, to those with a breadth of one- 

 half the height. . . . The mounds were usually of yellow 

 clay, although in one place the ground was of fine gravel, and 

 there the chimneys were of the same character. They were al- 

 ways circularly pyramidal in shape, the whole inside being very 

 smooth, but the outside was formed of irregular nodules of clay, 

 hardened in the sun, and lying just as they fell when dropped 

 from the top of the mound. A small quantity of grass and leaves 

 was mixed throughout the mound, but this was apparently 

 accidental." In no case did he find the burrows connected. 

 "Both males and females have burrows, but they were never 

 found together, each burrow having but a single individual." 

 Tarr's explanation of the presence of an extra oblique open- 

 ing is as follows : He thinks that tlie crayfish retire to the 



