cheek pouches. These are (_a_) the pocket gophers (Geomyidæ), which have
strong fore feet, relatively weak hind feet, and short tail, as compared
with weak fore feet, relatively strong hind feet, and long tail in the
other two; (_b_) the pocket mice (_Perognathus_), which are considerably
smaller than the kangaroo rats and lack the conspicuous white hip
stripe possessed by all the latter; and (_c_) the kangaroo rats
(_Dipodomys_).

[Illustration: FIG. 1.--Range, east of the Colorado River, of _Dipodomys
spectabilis spectabilis_ compared with that of _Dipodomys merriami_.
Cross hatching indicates area of overlapping of the two forms. The range
of _Dipodomys deserti_, not shown on the map, is west of that of
_spectabilis_, and so far as known the two do not overlap.]

_Dipodomys spectabilis spectabilis_ Merriam requires comparison with
three other forms of kangaroo rats in the same general region, namely,
_D. deserti_ Stephens, of approximately the same size, and _D. merriami_
Mearns and _D. ordii_ Woodhouse, the last two of decidedly smaller size.
The range of _deserti_ lies principally to the west of that of
_spectabilis_, and the two do not, so far as known, overlap. On the
other hand, _merriami_ and _ordii_, and subspecies, occur over a large
part of the range of _spectabilis_, living in very close proximity to
its burrows; _merriami_ is even suspected of pillaging the stores of
_spectabilis_. The range of _merriami_, however, is much more extensive
than that of _spectabilis_ (Fig. 1), which argues against a definite
ecological dependence or relationship. Separation of the four forms
mentioned may be easily accomplished by the following key:

_Key to Species of_ Dipodomys _in Arizona._