sh with more sharply contrasted white tip; interparietal
broader, distinctly separating mastoids (range in Arizona mainly
southeastern part) =Dipodomys spectabilis.=

_b^2_. Upper parts light ochraceous-buffy; tail pale brownish with
less sharply contrasted white tip; interparietal narrower, reduced
to mere spicule between mastoids (range in Arizona mainly
southwestern part) =Dipodomys deserti.=

_a^2_. Size much smaller (hind foot and greatest length of skull less
than 42 millimeters); tail not tipped with white.

_b^1_. Hind foot with four toes =Dipodomys merriami.=

_b^2_. Hind foot with five toes =Dipodomys ordii.=

On account of the small size, _merriami_ and _ordii_ do not require
detailed color comparison with the other two. The general color of the
upperparts of _spectabilis_ is much darker than that of _deserti_;
whereas _spectabilis_ is ochraceous-buff or light ochraceous-buff
grizzled with blackish, _deserti_ is near pale ochraceous-buff and lacks
the blackish.

The color of the upperparts alone amply suffices to distinguish
_spectabilis_ and _deserti_; but the different coloration of the tail is
the most obvious diagnostic feature. The near black of the middle
portion of the tail, the conspicuous white side stripes, and the pure
white tip make the tail of _spectabilis_ stand in rather vivid contrast
to the pale-brown and whitish tail of _deserti_.

The dens of the two larger species of _Dipodomys_--_spectabilis_ and
_deserti_--can be distinguished at a glance from those of the two
smaller--_merriami_ and _ordii_--by the fact that the mounds of the
former are usually of considerable size and the burrow mouths are of
greater diameter. On the Range Reserve _merriami_ erects no mounds, but
excavates its burrows in the open or at the base of _Prosopis_,
_Lycium_, or other brush. The mounds of _spectabilis_ are higher than
those of _deserti_, the entrances are larger, and they are located in
harder soil (Pl. III, Fig. 1). The dens of _deserti_ are usually more
extensive in surface area than those of _spectabilis_, and have a
greater number of openings (Pl. III, Fig. 2).

[Illustration: PLATE II. FIG. 1.--WINTER VIEW OF AREA INHABITED BY
KANGAROO RATS.

A water-hole scene on the U. S. Range Reserve at the base of the Santa
Rita Mountains, Ariz., where cooperative investigations a