closing is only occasional. Many occupied dens have not a single
opening closed. Further, night observations disclose that the inhabitant
of the mound will appear from some one of the two or three most-used
openings when night falls, and not necessarily from one which has been
closed by day. Recently an opening closed one day was observed in use
during the night, but was left open all the next day.

In attempting to determine whether there exist similarities of plan or
system in the dens, it was considered advisable to map them with some
degree of accuracy. This we were enabled to do by laying off a square
about a given mound, 2-1/2 or 3 meters each way, and subdividing it into
a series of small squares of half a meter on each side by drawing
cross-lines on the surface of the ground over the top of the mound. One
person then did the digging and exploring of the tunnels, as to
direction and depth, while the other noted the results on coordinate
paper (Figs. 2 and 3); the proper excavation and mapping of one of these
workings occupied from four to eight hours for the two.

[Illustration: FIG. 2.--Diagram of a typical den of _Dipodomys
spectabilis spectabilis_. Double shading indicates where one portion of
tunnel lies above another and solid black a three-story arrangement;
_A_, _B_, _C_, etc., active openings to surface; figures without arrows,
depths in centimeters to tunnel roofs; figures with arrows, tunnel
widths in centimeters; _N._ nest chamber; _S_, storage; _OS_, old
storage; _Y_, probably an old nest chamber; _Z_, old, unused, or
partially plugged openings.]

While there is greater complexity in the larger, and probably older,
mounds than in the smaller, all are extremely complicated and can only
be described as labyrinthine in character. The tunnels wind about