_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. No evidence of intergradation with any other race was noted. To the south the range of _D. o. evexus_ is separated from that of _D. o. montanus_ by a high, transverse ridge of the Rocky Mountains which is inhospitable to these animals. Much territory inhospitable to _Dipodomys_ intervenes also between the ranges of _D. o. evexus_ and _D. o. luteolus_, but there are areas connecting the northern part of the range of _D. o. evexus_ and the southwestern part of the known range of _D. o. luteolus_, in which _Dipodomys_ may occur. If kangaroo rats occur in these areas it is to be expected that they will show intergradation between the two subspecies concerned. _Specimens examined._--Total, 24, all from Colorado, distributed as follows: _Chaffee County_: Salida, 10 (3 USBS; 7 AMNH). _Fremont County_: Canyon City, 13 (USBS). _Pueblo County_: Pueblo, 1 (USBS). =Dipodomys ordii medius= new subspecies