Type.—Male, adult, no. 20957, Amer. Mus. Nat. Hist.; Rio Sestin, northwestern Durango, Mexico; obtained on April 13, 1903, by J. H. Batty. (Type not seen.)
Range.—Northwestern and northern Durango, Mexico; marginal localities are: Rosario, Rio Sestin, Mt. San Gabriel, Rio del Bocas, Villa Ocampo.
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).