PANAMINTINUS GROUP.--Composed of all the now known subspecies of _Dipodomys panamintinus_ and the species _Dipodomys stephensi_, if the latter is a full species. This group was included by Grinnell in the Heermanni group, with which it agrees in broadness of the maxillary arches and the configuration of the penis bone, but on the basis of the degree of specialization, as indicated by the indices (see Table 1), I feel that the Panamintinus group is more properly placed after the Ordii group and should be separated from the Heermanni group. Actually, animals in the Panamintinus group are intermediate between those of the Ordii and Heermanni groups. HEERMANNI GROUP.--Composed of the subspecies of _Dipodomys heermanni_ and _Dipodomys agilis_, the species _Dipodomys ingens_, _Dipodomys venustus_ and _Dipodomys elephantinus_. _D._ _ingens_ even though larger in linear measurements than any of the other kinds included in this group, has almost the same degree of specialization as does _D. heermanni_. _D. agilis_, even though somewhat less specialized than the other kinds placed in this group, by the general nature of the indices, by the form of the visceral mass and to some degree by the shape of the baculum, shows itself properly to belong with this group. The species _D. venustus_, judged by characters of the visceral anatomy, also belongs here rather than with some other group or as a separate group. From the appearance of the visceral mass, _D. venustus_ is somewhat more specialized than either _D. heermanni_ or _D. agilis_, but _D. venustus_ does show its affinities with this group. The species _D. elephantinus_ has not been examined as thoroughly as have the other species but the external morphology and the configuration of the cranium place it with this group. SPECTABILIS GROUP.--Composed of the subspecies of _Dipodomys spectabilis_. In two of the six indices, _D. spectabilis_ shows a high degree of specialization toward saltation, but in the other four indices it shows a relatively low degree of specialization or is average for the genus. Burt (1936:155) placed _D. spectabilis_ with _D. deserti_ on the basis of the baculum alone. I have not examined _D. nelsoni_ but place it with this group as did also Grinnell and Davis.