involve a considerable increase in height. They are frequently located
at junction points of two or more branches of the tunnel system.

The nest cavity is a chamber of approximately spherical shape and from
17 to 23 centimeters in diameter. Chambers of this character were
observed and noted as "old storage" in a number of cases. They were
sometimes cut off from the rest of the habitation, and at first were
supposed to contain abandoned musty storage. As experience in excavating
and interpreting results has been gained we have concluded that these
chambers in fact represent abandoned nests.

[Illustration: FIG. 3.--Diagram of the system of surface runways and
subsidiary dens of _Dipodomys spectabilis spectabilis_. The underground
tunnels of the main den were too complicated to illustrate on this
scale, being very similar to those of Figure 2. The underground tunnels
of the subsidiaries are shown in solid black. Some runways fade out in
the grass in a manner that can not be indicated in a line drawing.]

Bailey gives the dimensions of nest chambers observed in New Mexico as
about 6 by 8 inches to 8 by 10 inches. The nest is composed of finer,
softer, and more chaffy material than the regular storage. The chaff
refuse from the food probably contributes largely to it, though some
leaves of grasses not stored for food may also be found, and a nest,
especially the one in use, may be distinguished, if excavating is
carefully done, by the distinct cavity about the size of a fist in its
interior (Pl. IX, Fig. 1). One may sometimes find this cavity distinctly
warm from the recent presence of the inhabitant.

The walls or partitions between the chambers and tunnels are in places
surprisingly thin, and it is no wonder that one is almost certain to