_Diagnosis._--Size small (see measurements). Color dark, entire dorsal surface (_16''_) between Pinkish Cinnamon and Cinnamon-Buff, purest on sides, flanks and cheeks, upper parts strongly suffused with black; arietiform markings, plantar surfaces of hind feet, pinnae of ears, dorsal and ventral stripes of tail, brownish. Skull of medium size, nasals long and flared distally; rostrum long and narrow; interorbital region relatively narrow; auditory bullae less inflated than in _Dipodomys ordii palmeri_; interparietal region narrow; zygomatic arches heavy and bowed laterad; pterygoid fossae ovoid; braincase but slightly vaulted. _Comparisons._--From _Dipodomys ordii palmeri_, _D. o. obscurus_ differs in: Size larger; color lighter; nasals shorter and more flared distally; interorbital width less; lacrimal processes larger; auditory bullae less inflated; pterygoid fossae ovoid as opposed to subcircular; zygomatic arches heavier; rostrum shorter and wider. From _Dipodomys ordii ordii_, _D. o. obscurus_ differs as follows: Size smaller; color darker; skull smaller; nasals longer; rostrum narrower and shorter; interorbital width greater; interparietal region narrower; narrower across auditory bullae; zygomatic arches heavier and more bowed laterally; pterygoid fossae more ovoid; breadth across maxillary arches greater; external auditory meatus smaller. With _Dipodomys ordii attenuatus_ and _Dipodomys ordii sennetti_, _D. o. obscurus_ needs no comparison since it is larger and darker than either of those subspecies and can readily be told from the latter by the greater expansion of the auditory bullae. For comparison with _Dipodomys ordii fuscus_ see account of that subspecies. _Remarks._--_D. o. obscurus_ seemingly is not a far-ranging subspecies. The only examples referable to it come from a relatively restricted area of Durango, Mexico. One specimen from Rio del Bocas, Durango, is not typical and shows the characters described for the animals from Chihuahua City and from Casas Grandes. I have considered the possibility that this specimen is an intergrade between _D. o. obscurus_ and an unnamed subspecies ranging to the northeastward. The other specimens in the series from Rio del Bocas are typical of _D. o. obscurus_. _Specimens examined._--Total, 69, all from Durango, distributed as follows: Rosario, 20 (AMNH); Villa Ocampo, 5 (AMNH); Rio Sestin, 30 (28 AMNH; 2 CNHM); Mt. San Gabriel, 2 (AMNH); Rio del Bocas, 11 (AMNH); Rancho Santuario, 1 (AMNH). [Illustration: FIG. 24. Known occurrences and probable geographic range of the subspecies of _Dipodomys ordii_ in the southeastern fourth of the range of the species.