Perodipus montanus richardsoni [Warren], Mammals of Colorado, p. 76, 1910 (part—the part from Salida, Colorado).
Type.—Male, adult, no. 150990, U. S. Nat. Mus. Biol. Surv. Coll.; Salida, Chaffee County, Colorado (altitude 7000 ft.); obtained on November 10, 1907, by Merritt Cary, original no. 1245.
Range.—Upper Arkansas River Valley of south-central Colorado, from Salida to Pueblo.
Diagnosis.—Size large (see measurements). Color dark, entire dorsal surface between (16") Pinkish Cinnamon and Cinnamon-Buff, 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 of medium size; rostrum short and wide; nasals short; auditory bullae but slightly inflated; braincase but slightly vaulted.
Comparisons.—From Dipodomys ordii richardsoni, D. o. evexus differs as follows: Size smaller in all measurements taken; color darker; ears darker, dorsal and ventral stripes on tail darker, arietiform markings darker and more distinct, plantar surfaces of hind feet darker; skull smaller in all measurements; length, as expressed in percentage of width of skull, greater in D. o. evexus (66 per cent in D. o. evexus, 62 per cent in D. o. richardsoni which gives the appearance of a long, narrow skull as contrasted with a rather short, wide skull); auditory bullae less expanded laterally, posteriorly and ventrally; interparietal region relatively wider in proportion to greatest width across auditory bullae; cutting edge of upper incisors narrower; pterygoid fossae smaller and more nearly circular.
Compared with Dipodomys ordii luteolus, D. o. evexus differs as follows: Size somewhat smaller in external measurements; color darker in all pigmented areas; skull smaller in two of the seven measurements taken but in the other five measurements somewhat larger; auditory bullae less inflated; cutting edge of upper incisors narrower; zygomatic arch heavier; pterygoid fossae smaller and more nearly circular; external auditory meatus ovoid as contrasted to nearly circular; paroccipital processes smaller.
From Dipodomys ordii nexilis, D. o. evexus differs in: Color darker; rostrum wider and shorter; interorbital region wider; breadth across maxillary arches greater; auditory bullae less inflated; interparietal region larger; zygomatic arches heavy and bowed laterad; molariform teeth smaller; cutting edge of upper incisors narrower.
For comparison with Dipodomys ordii montanus see account of that subspecies.
Remarks.—This race of kangaroo rat, described from the upper Arkansas River Valley, closely resembles Dipodomys ordii luteolus but differs in darker color, slightly smaller body and larger skull.