Remarks.--This race of _Dipodomys ordii_ is readily distinguished from _Dipodomys ordii evexus_, from the valley of the upper Arkansas River, by larger size, larger skull and lighter color. Intergradation with _Dipodomys ordii luteolus_ occurs rather freely in northeastern Colorado, as indicated by specimens from 3 miles northeast of Fitzsimmons, 6 miles east and 1 mile north of Denver and Barr Lake. These specimens resemble _D. o. richardsoni_ in light color, greater inflation of the auditory bullae and the shape of the pterygoid fossae but resemble _D. o. luteolus_, to which they are here referred, in the length of the nasals, the least interorbital width and in the external measurements. In the southern part of the range of _D. o. richardsoni_ intergradation occurs with _Dipodomys ordii medius_, as at 6 miles southwest of Muleshoe, Texas. Specimens from there have the long, wide rostrum and narrow skull of _D. o. richardsoni_ but in the sum total of their characters more closely resemble _D. o. medius_. At Texline, Texas, the animals show intergradation in the length and shape of the nasals and degree of convexity of the cranium but are referable to _D. o. richardsoni_. In fine, intergradation occurs at all points where the range of _D. o. richardsoni_ touches that of any other geographic race. No one series of it is as uniform as are most series of specimens of other known races. _Dipodomys ordii richardsoni_ shows a mixture of characters. Nevertheless, each of the populations studied has characters in most of the animals that make this form recognizable as a taxonomic unit--a unit that seems, as yet, not to have become stabilized even in the central parts of its range. Coues and Allen (1877:542) list specimens from Fort Cobb, Arkansas. It is known that the Post Office Department, for administrative purposes, attached certain towns and military installations in Indian Territory (now Oklahoma) to the State of Arkansas. Thus it is apparent that Fort Cobb, Arkansas, as recorded by Coues and Allen (_loc. cit._) is Fort Cobb, Oklahoma. Specimens from Fort Cobb would be expected to be _D. o. richardsoni_. _Specimens examined._--Total, 351, distributed as follows: =Nebraska=: _Adams County_: Bladen, 10 (AMNH). _Dundy County_: Haigler, 1 (USBS). =Colorado=: _Crowley County_: Olney, 1 (USBS). _Kiowa County_: Chivington, 3 (USBS). _Otero County_: 18 mi. S La Junta, 4 (AMNH); Higbee, 1 (USBS). _Bent County_: 4 mi. SE Las Animas, 4100 ft., 3 (MVZ). _Prowers County_: Lamar, 9 (LACM); 1 mi. S Lamar, 4000 ft., 11 (KU). _Baca County_: Gaumes Ranch, 4600 ft., NW Corner, 1 (USBS).