The species _M. macroura_ is restricted to the arid region made up mostly of the Mexican Plateau. Also, wherever the species occurs beyond this Plateau, as for example in Guatemala, at San Mateo del Mar in Oaxaca, in the vicinity of Piedras Negras in Veracruz, and in southern Arizona, aridity is marked. Whether the species has a continuous distribution from the southern end of the Mexican tableland southward to Duenas in Guatemala is not known but it is unlikely that the lowland population at San Mateo del Mar on the Pacific slope of Oaxaca has contact with _M. m. macroura_ of the Mexican Plateau and it is almost certain that the population, which is here named _M. m. eximius_, from the arid coastal plain of eastern Mexico in Veracruz, has no connection with the upland population, _M. m. macroura_. The lowest elevation on the eastern slope of the Plateau from which we have record of the occurrence of this species is 4,500 feet at Jico. All along the eastern slope of the Plateau, between the elevations of approximately 2,000 and 4,500 feet, the belt of lush, dense vegetation of the upper humid division of the Tropical Life-zone constitutes a barrier to _Mephitis_ and tends to exclude the hooded skunk from the arid territory below the humid belt. Another kind of skunk, _Conepatus tropicalis_, lives in the humid belt, at least on the eastern side of the Mexican tableland. How the population of _Mephitis_, which was sampled by us from west and west-northwest of Piedras Negras, arrived there is unknown but we think that its geographic range is not now connected with that of the population on the Plateau. The same can be said of the lowland population at San Mateo del Mar in Oaxaca. There, on the Pacific slope of the Mexican tableland, the lower humid division of the Tropical Life-zone probably has tended to restrict the spread southward and westward of _Mephitis_; however, on this Pacific slope the humid belt is less humid and it is less continuous, we think, than on the Atlantic slope. Four subspecies of _Mephitis macroura_ may be recognized. They are as follows: #Mephitis macroura milleri# Mearns 1897. _Mephitis milleri_ Mearns, Proc. U. S. Nat. Mus., 20:467, 1897. 1901. _Mephitis macroura milleri_, Bull. Amer. Mus. Nat. Hist., 14:334, November 12, 1901. _Type locality._--Fort Lowell, Pima County, Arizona. _Range._--Northwestern Mexico and southeastern Arizona. See figure 1. Marginal occurrences (unless otherwise indicated, after Howell, N. Amer. Fauna, 20:42, 43, 1901) are: _Arizona_: Santa Catalina Mountains; Tucson; Fort Lowell. _Chihuahua_: Casas Grandes; Chihuahua (City). _Coahuila_: La Ventura. _Chihuahua_: Guadalupe y Calvo (mountains near). _Sonora_: Camoa; Hermosillo; Sierra Cubabi (Burt, Miscl. Publ., Mus. Zool., Univ. Michigan, 39:30, 1938). _Characters._--Long skull ([Male] 60 mm, [Female] 56 mm) and large m1.