=Dipodomys ordii montanus= Baird _Dipodomys montanus_ Baird, Proc. Acad. Nat. Sci. Philadelphia, 7:334, April, 1855. _Perodipus montanus_, Merriam, Proc. Biol. Soc. Washington, 17:140, July 14, 1904. _Perodipus ordii montanus_, Goldman, Proc. Biol. Soc. Washington, 30:113, May 23, 1917. _Dipodomys ordii montanus_, Grinnell, Journ. Mamm., 2:96, May 2, 1921. _Type._--Male, no. 490/1631, U. S. Nat. Mus.; near Fort Massachusetts, Costilla County, Colorado; obtained in 1853 by F. Kreutzfeldt (Pacific Railroad Survey). _Range._--The San Luis Valley of south-central Colorado and north-central New Mexico; marginal occurrence are: in Colorado, 22 mi. E Mosca, Saguache, Alamosa and Antonito; in New Mexico, 4 mi. SW Cimmaron. _Diagnosis._--Size small (see measurements). Color dark, entire dorsal surface between (_c_) Vinaceous-Buff and Avellaneous, purest on sides and flanks, upper parts strongly suffused with black; arietiform markings, pinnae of ears, plantar surfaces of hind feet and dorsal and ventral stripes of tail, blackish. Skull small; rostrum slender; interorbital width narrow; auditory bullae strongly inflated; braincase but slightly vaulted; interparietal region wide; zygomatic arch bowed laterally. _Comparisons._--From _Dipodomys ordii richardsoni_, _D. o. montanus_ differs as follows: Size smaller; color darker in all pigmented areas; ventral stripe of tail continuous to end of pencil in all specimens, whereas in _D. o. richardsoni_ the stripe is incomplete in most specimens. In all specimens the dorsal and ventral stripes of the tail are darker in _D. o. montanus_; skull smaller in all measurements taken; jugal straight or nearly so, as contrasted to bowed laterally; pterygoid fossae shallower and more ovoid, that is to say, wings of pterygoid flare laterally; ventral projection of auditory bullae more pronounced; rostrum, immediately in front of zygomatic process of maxilla, nearly parallel to median plane along long axis of skull, while in _D. o. richardsoni_ this union forms a decided obtuse angle; paroccipital processes smaller; foramen magnum smaller and more ovoid as opposed to larger and more circular.