_Comparisons._--From _Dipodomys ordii terrosus_, _D. o. luteolus_ differs as follows: Size smaller, except that tail and ear are longer; color lighter in all pigmented areas; skull smaller in every measurement taken; auditory bullae less inflated; zygomatic processes of maxillae smaller; cutting edge of upper incisors narrower; zygomatic arch weaker. From _Dipodomys ordii priscus_, _D. o. luteolus_ differs in: Size larger except hind foot which is shorter; dorsal and ventral stripes of tail, plantar surfaces of hind feet, arietiform markings and pinnae of ears, in most specimens, darker; auditory bullae less inflated; nasals shorter; rostrum wider; total length of skull shorter; zygomatic arch weaker; foramen magnum more ovate. From _Dipodomys ordii evexus_, _D. o. luteolus_ differs as follows: Hind foot longer; color lighter in all pigmented areas; auditory bullae more inflated; pterygoid fossae more expanded laterally; width across maxillary arches less; interorbital region narrower; zygomatic arch weaker; external auditory meatus almost round as opposed to ovoid. Comparison with _Dipodomys ordii richardsoni_ is made in account of that subspecies. _Remarks._--_Dipodomys ordii luteolus_ resembles _D. o. priscus_ in size and color but can readily be told from it and _D. o. richardsoni_ when specimens from the central portions of the ranges of the subspecies are compared. At and near the periphery of the range, especially in that part which adjoins the range of _D. o. richardsoni_, intergradation occurs. Specimens from Kennedy, Perch and Neligh, Nebraska, approach _D. o. richardsoni_ in the shape of the pterygoid fossae and nasal bones, but in all other characters they resemble _D. o. luteolus_ to which subspecies they are here referred. Specimens from Loveland and 20 miles east of Avalo, Colorado, show intergradation with _D. o. richardsoni_ in the width of the rostrum and size of the zygomatic arch but are referable to _D. o. luteolus_. No specimens here referred to _D. o. luteolus_ were found to intergrade with _D. o. priscus_. _Specimens examined._--Total, 250, distributed as follows: =South Dakota=: _Perkins County_: 9 mi. N Bison, 8 (MVZ). _Meade County_: Smithsville, 2 (USBS). _Jackson County_: 20 mi. SSE Phillip, in Haakon County, 1 (MVZ). _Custer County_: Elk Mountain, 1 (MHS); Buffalo Gap, 2 (USNM). _Bennett County_: Big Spring Canyon, Batesland, 7 (CNHM); Rosebud Indian Agency, 1 (USBS). =Wyoming=: _Fremont County_: 2-1/2 mi. W Shoshoni, 80 (KU); Granite Mountain, 1 (UM). _Natrona County_: 1 mi. NE Casper, 19 (KU); Casper, 7 (USBS); Sun, 8 (USBS). _Converse County_: Douglas, 2 (USBS). _Niobrara County_: Van Tassel Creek, 1 (CM). _Carbon County_: Fort Steele, 1 (USBS). _Goshen County_: Rawhide Butte, 1 (USBS).