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.