FIG. 12. _Dipodomys ordii oklahomae_, [F], adult, no. 265456, USBS; 2-1/4 mi. S Norman, Cleveland County, Oklahoma; 21 March, 1934. FIG. 13. _Dipodomys ordii richardsoni_, [F], adult, no. 15995, KU; 1 mi. S Lamar, Prowers County, Colorado; 8 September, 1945. FIG. 14. _Dipodomys ordii nexilis_, [F], adult, no. 149941, USBS; 5 mi. W. Naturita, Montrose County, Colorado; 20 July, 1907. FIG. 15. _Dipodomys deserti deserti_, [F], adult, no. 18670, KU; 14 mi. WSW Fallon, Churchill County, Nevada; 3 November, 1945.] [Illustration: FIGS. 16-20. Dorsal views of skulls showing the degrees of inflation of the auditory bullae and the correlation of large bullae with small interparietal. All figures approximately × 1. FIG. 16. _Dipodomys ordii compactus_, for data see Fig. 11. FIG. 17. _Dipodomys ordii oklahomae_, for data see Fig. 12. FIG. 18. _Dipodomys ordii richardsoni_, for data see Fig. 13. FIG. 19. _Dipodomys ordii nexilis_, for data see Fig. 14. FIG. 20. _Dipodomys deserti deserti_, for data see Fig. 15.] Wood (1935:155), on the basis of structure of the teeth, listed the species which he examined in the following increasing order of specialization: _Dipodomys compactus_ (now _Dipodomys ordii compactus_), _D. nitratoides_, _D. merriami_, _D. ordii_, _D. agilis_, _D. herrmanni_, _D. spectabilis_, and _D. deserti_. This arrangement is at variance with that of Grinnell (1922) who listed the species in order of increasing specialization as: _Dipodomys herrmanni_, _D. panamintinus_, _D. ingens_, _D. spectabilis_, _D. merriami_, _D. nitratoides_, _D. ordii_, _D. agilis_, _D. venustus_, _D. microps_ and _D. deserti_. As noted, the only agreement between the two arrangements is the placing of _D. deserti_ as the most specialized. Relying on skeletal indices alone, I would accord the same position to _D. deserti_ but would not arrange the other species as have either Wood or Grinnell. In this study, the amount of specialization of each species, as indicated by the skeleton, was determined by assigning consecutive numbers from 1 to 11 to each species in its place in each index, and then totaling and averaging these arbitrary numbers (Table 3). It will be noted that there is a tendency for each species to occupy the same relative position in each of the indices. It is felt, however, that a more nearly correct arrangement, according to degree of specialization, is obtained by using the six skeletal indices plus the information obtained from the study of the viscera. On this basis the species may be arranged from least to most specialized as follows: _Dipodomys ordii_, _D. microps_, _D. panamintinus_, _D. agilis_, _D. herrmanni_, _D. ingens_, _D. spectabilis_, _D. phillipsii_, _D. merriami_, _D. nitratoides_ and _D. deserti_.