little
retreats whenever disturbed, and swim away down stream out of sight.
They were often found some distance from the main stream under rocks
that had been covered by the brook at a higher watermark; but although
there was very little water under the rocks, and the stream had not
covered them for at least two weeks, they showed no tendency to burrow.
Nor have I ever found any burrows formed by the river species _Cumbarus
affinis._ although I have searched over miles of marsh land on the
Potomac for this purpose.

[Illustration: Fig. 2 Crayfish Mound (shorter)]

The brook near where my observations were made was fast decreasing in
volume, and would probably continue to do so until in July its bed would
be nearly dry. During the wet seasons the meadow is itself covered. Even
in the banks of the stream, then under water, there were holes, but they
all extended obliquely without exception, there being no perpendicular
burrows and no mounds. The holes extended in about six inches, and there
was never a perpendicular branch, nor even an enlargement at the end. I
always found the inhabitant near the mouth, and by quickly cutting off
the rear part of the hole could force him out, but unless forcibly
driven out it would never leave the hole, not even when a stick was
thrust in behind it. It was undoubtedly this species that Dr. Godman
mentioned in his "Rambles of a Naturalist," and which Dr. Abbott _(Am.
Nal.,_ 1873, p. 81) refers to _C. bartonii_. Although I have no proof
that this is so, I am inclined to believe that the burrowing crayfishes
retire to the stream in winter and remain there until early spring, when
they construct their burrows for the purpose of rearing their young and
escaping the summer droughts. My reason for saying this is that I found
one burrow which on my first visit was but six inches deep, and later
had been projected to a depth at least twice as great, and the
inhabitant was an old female.

I think that after the winter has passed, and while the marsh is still
covered with water, impregnation takes place and burrows are immediately
begun. I do not believe that the same burrow is occupied for more than
one year, as it would probably fill up during the winter. At first it
burrows diagonally, and as long as the mouth is covered with water is
satisfied with this oblique hole. When the water recedes, leaving the
opening uncovered, the burrow must be dug deeper, and the economy of a
perpendicular burro