[Illustration:  Fig. 1 Section of Crayfish burrow]

The length, width, general direction of the burrows, and number of the openings were extremely variable, and the same is true of the mounds.  Fig. 1 illustrates a typical burrow shown in section.  Here the main burrow is very nearly perpendicular, there being but one oblique opening having a very small mound, and the main mound is somewhat wider than long.  Occasionally the burrows are very tortuous, and there are often two or three extra openings, each sometimes covered by a mound.  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 one-half the height.  The typical mound is one which covers the perpendicular burrow in Fig. 1, its dimensions being six inches broad and four high.  Two other forms are shown in Fig. 2.  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.  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 always circularly pyramidal in shape, the hole 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 through the mound, but this was apparently accidental.

The size of the burrows varied from half an inch to two inches in diameter, being smooth for the entire distance, and nearly uniform in width.  Where the burrow was far distant from the stream, the upper part was hard and dry.  In the deeper holes I invariably found several enlargements at various points in the burrow.  Some burrows were three feet deep, indeed they all go down to water, and, as the water in the ground lowers, the burrow is undoubtedly projected deeper.  The diagonal openings never at that season of the year have perfect chimneys, and seldom more than a mere rim.  In no case did I find any connection between two different burrows.  In digging after the inhabitants I was seldom able to secure a specimen from the deeper burrows, for I found that the animal always retreated to the extreme end, and when it could go no farther would use its claws in defense.  Both males and females have burrows, but they were never found together, each burrow having but a single individual.  There is seldom more than a pint of water in each hole, and this is muddy and hardly suitable to sustain life.

[Illustration:  Fig. 2 Crayfish Mound]