_Comparisons._--From _Thomomys talpoides rostralis_ (North Platte River Valley, SW of Saratoga, Wyoming), the subspecies to the east and south, _T. t. meritus_ differs in: Lesser size, darker color, smaller and slenderer skull. The slenderness is especially noticeable in the breadth across the zygomata, mastoids, and rostrum. From _Thomomys talpoides clusius_ (topotypes), the subspecies to the north and west, _T. t. meritus_ differs in: Color much darker; rostrum longer; skull narrower across mastoids and zygomata; tympanic, and also mastoid, bullae smaller. Resemblance to _T. t. clusius_ is shown in the narrowness of the skull interorbitally and in the shortness of the tooth-row. _Remarks._--The specimens of _Thomomys_ from Wyoming on which the name _T. t. meritus_ is based were obtained by Mr. E. Lendell Cockrum and his associates with the thought that intergradation might be shown between _T. t. rostralis_ to the east and _T. t. clusius_ to the west. The animals showed instead, that there was a subspecies differing from each of the two mentioned subspecies in small size, dark color and slenderness of skull. Acknowledgment of assistance with field work is made to the Kansas University Endowment Association. _Measurements._--Average and extreme measurements of seven adult males and five adult females, from the type locality, are as follows: Total length, [Male] 204 (193-226), [Female] 207 (193-210); length of tail, 56 (46-68), 56 (50-63); length of hind foot, 27.6 (26-30), 27.4 (27-28); basilar length, 30.7 (29.0-33.0), 30.1 (29.5-30.7); zygomatic breadth, 20.4 (18.9-21.6), 19.5 (18.8-20.0); least interorbital breadth, 6.2 (5.8-6.6), 6.1 (5.9-6.3); mastoidal breadth, 17.9 (16.9-18.5), 17.2 (16.7-17.6); length of nasals, 13.7 (12.4-14.7), 13.2 (12.8-13.9); breadth of rostrum, 7.0 (6.5-7.5), 6.9 (6.7-7.3); length of rostrum, 16.3 (15.3-17.5), 15.8 (15.3-16.1); alveolar length of maxillary tooth-row, 7.1 (6.9-7.3), 7.1 (6.8-7.5). _Specimens examined._--Total number 26 and unless otherwise indicated in the Museum of Natural History of the University of Kansas. #Wyoming.#--_Carbon County_: Savery (8 mi. N and 19-1/2 mi. E, 8800 ft., 12; 7 mi. N and 17 mi. E, 8300 ft., 1; 6 mi. N and 12-1/2 mi. E, 8400 ft., 1; 6 mi. N and 13-1/2 mi. E, 8400 ft., 2; 6 mi. N and 14-1/2 mi. E, 8350 ft., 1; 5 mi. N and 3 mi. E, 6800 ft., 1; 4 mi. N and 8 mi. E, 7800 ft., 7300 ft., 3; 4 mi. N and 10 mi. E, 7800 ft., 3) 24. #Colorado#--_Routt Co._ ?: Elkhead Mts., 20 mi. SE Slater, 2 (U. S. B. S.). _Museum of Natural History, University of Kansas, Lawrence. Transmitted October 20, 1951._ 24-1359