E. Raymond Hall

“ Comparisons.—In comparison with T. t. fossor and T. t. rostralis, which occur farther west, selected differences of T. t. retrorsus are: lighter color; larger skull; more inflated tympanic bullae; greater relative (to length of skull) breadth across upper incisors, rostrum, and zygomata. The difference in color is greater in comparison with fossor than with rostralis.
In comparison with T. t. macrotis (specimens from the type locality) , T. t. retrorsus is indistinguishable in color, length of tail, and length of tooth-row, but averages smaller in all other measurements. ”

“ The subspecific identity of the animals from east-central Colorado thus is left in doubt. Examination of pertinent materials was made in the expectation that the names Thomomys talpoides macrotis F. W. Miller (Proc. Colorado Mus. Nat. Hist., 9:41, December 14, 1930) and Thomomys talpoides cheyennensis Swenk (Missouri Valley Fauna, 4:5, March 1, 1941) would apply to the specimens, the identity of which is in doubt. ”

“ Linear measurements of the two latter structures and length of tail are approximately the same in the two subspecies but all other measurements average more in T. t. retrorsus. Also in the latter the temporal lines are approximately parallel instead of being bowed outward in their middle extent and instead of being more widely separated posteriorly than anteriorly. ”