The geographic range of the kangaroo rats, genus _Dipodomys_, extends
from southern Canada south to the southern limits of the Mexican
Tableland and from the Pacific Coast east to the eastern limits of the
Great Plains in Kansas, Oklahoma and Nebraska. These animals are usually
restricted to sandy soils in semiarid regions. The species _Dipodomys
ordii_, with which this account is primarily concerned, is, to the best
of my knowledge, almost exclusively confined to sandy areas.
Since 1841, when Gray gave the generic name _Dipodomys_ to the kangaroo
rats, basing the name on the four-toed species _Dipodomys phillipsi_,
several other generic names have been applied. Fitzinger, in 1867, used
the name _Perodipus_ for those animals with five toes on the hind foot,
designating _Dipodomys agilis_ as the type of his genus. In 1890,
Merriam proposed the generic name _Dipodops_ with _Dipodomys agilis_ as
the type, apparently being unaware of Fitzinger's name, _Perodipus_.
Trouessart, in 1897, through what was an apparent _lapsus calami_,
applied the generic name _Cricetodipus_ Peale to all of the species of
the then known genera _Perodipus_ and _Dipodomys_, but Trouessart later,
1904 or 1905, in his Supplementum, corrected this _lapsus_ and used the
names _Dipodomys_ and _Perodipus_. Grinnell (1919:203) showed that some
of the four-toed _Dipodomys_ had five toes on one hind foot and four on
the other and that _Perodipus_ must fall as a synonym of the earlier
generic name _Dipodomys_ which was to be applied to all of the kangaroo
rats.
_Dipodomys ordii_ was named by Woodhouse in 1853, from specimens from El
Paso, Texas, but between that time and 1919 the name _ordii_ was used in
combination with all of the generic names mentioned above (see
synonymies under the accounts of the subspecies).
The nearest approach to a revision of the genus was Grinnell's (1922) "A
Geographical Study of the Kangaroo Rats of California." Since that time,
Hall and Dale (1939) revised the _D. microps_ group and Durrant and
Setzer (1945) reported upon the kangaroo rats of Utah. The present paper
is a review of the species _Dipodomys ordii_. Some of the objectives in
this review have been to learn: (1) What kinds of kangaroo rats are
subspecies of the species _Dipodomys ordii_; (2) the limits of
geographic range of this full species; (3) the extremes of color, and of
size and shape of the skull in this one species; (4) the significance
of different sizes, shapes and colors; (5) the reasons for the
existence, or formation, of selected subspecies; and (6) the
relationships of _Dipodomys ordii_ to other species in the genus.