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. METHODS AND ACKNOWLEDGMENTS Available specimens were arranged according to geographic origin. These were segregated as to sex and then under each sex by age. Individual variation was next measured in each of several samples in which individuals were of like geographic origin, sex, age and season. Finally, comparable materials were arranged geographically for detection of variations of systematic worth. Following preliminary studies of material thus arranged, additional specimens were collected from critical areas. When fully adult animals (see next paragraph) were segregated as to sex, and then measured, the degree of secondary sexual variation was found to be less than the degree of individual variation; therefore in the tables of indices, no distinction as to sex has been made.