Four adults and one subadult from Trinidad are intergrades between _N. m. scopulorum_ and _N. m. fallax_, perhaps more nearly resembling the former. In pelage they are indistinguishable from specimens of _fallax_ from Gold Hill (the type locality), less buff than most individuals of _scopulorum_ from Otero, Prowers, and Baca counties. The skulls of the three fully mature adults are large with a wide zygomatic breadth, large rostrum, and large upper incisors as in _scopulorum_; but the upper molars are small and the bullae are rather small and narrow as in _fallax_. In the degree of arching at the base of the rostrum, the shape of the frontal, the shape of the interparietal, and the size of the upper molars, the specimens from Trinidad are intermediate. It seems to me best to refer them to _scopulorum_. Two first-year adults from Fisher Peak and Long Canyon are indistinguishable from topotypes of _fallax_ of similar age and also resemble a young adult and a subadult from Trinidad, but all are insufficiently mature to show subspecific characters distinctly. Until adequate series are available from southwestern Las Animas County it seems best to regard all specimens from the three localities as representatives of a single uniform population which is intermediate between _fallax_ and _scopulorum_ but more nearly like the latter. Unfortunately no other specimens are available from the foothill zone south of the Arkansas River where morphological intergradation and ecological transition between _fallax_ and _scopulorum_ might reasonably be expected to occur. Three specimens from the north side of the Arkansas River, about 26 miles below Canyon City, Pueblo County, are like _fallax_ in size, dorsal profile of the skull, and shape of the interorbital constriction; but they approach _scopulorum_ in shape of the interparietal, size of the rostrum, and size of the molars. They are intergrades referrable to _fallax_. _Neotoma mexicana_ was first reported from Oklahoma by W. Frank Blair in 1939 (Amer. Midl. Nat., 22:126) who referred a specimen from Tesequite Canyon, Cimarron County, to _N. m. fallax_. I have seen one specimen (MZ 80469) from Tesequite Canyon and refer it to _scopulorum_. Of _scopulorum_, each of eight skulls, of the 28 skulls examined, has an anteroexternal enamel fold on the m3 and one (BSC 35222/47487 [Male]) has an anterointernal fold on the m3. Of the other 19 mandibles, a few are too old to show such a fold, which tends to be obliterated with wear in later age, and the others lack the fold.