Of the seven other Mexican _Geophis_ having 15 rows of scales, four species (_cancellatus_, _dugesii_, _chalybeus_, and _semidoliatus_) have alternating pale and dark transverse markings and therefore superficially resemble _aquilonaris_. Of the latter two species, the poorly known _G. chalybeus_ (Veracruz) has a much lower (137 to 142) number of ventrals than _aquilonaris_, and _G. semidoliatus_ (southeastern Mexico--Veracruz, Hidalgo, and Oaxaca) has a narrower head, fewer supralabials (four to five with only the third entering the orbit), and fewer ventrals (136 to 169) than _aquilonaris_. _Geophis aquilonaris_ seems to be most closely allied to _G. cancellatus_ (Chicharras, Chiapas) and _G. dugesii_ (known from two localities in northern Michoacán); all three species resemble one another in the number and arrangement of the scales of the head, in general coloration, and in having relatively high numbers of ventral scales (171 in _cancellatus_, 150 to 164 in _dugesii_). _G. cancellatus_ differs from the other two species in lacking internasal scales. _Geophis aquilonaris_ differs from both species in having a higher number of ventral and subcaudal scales, a longer tail (tail contained in snout-vent length three to four times in _aquilonaris_, four and one half to six times in _dugesii_, 11 to 12 times in _cancellatus_), and in having more bands on the body (28 to 32 in _cancel latus_, two to seven in _dugesii_). The belly in _dugesii_ and _cancellatus_ is pale but in _aquilonaris_ it is ringed or of a solid dark color. As more specimens of _Geophis_ become available from intermediate localities in Mexico, it will perhaps be demonstrated that many of the kinds now thought of as full species (including those discussed above) are subspecies of a few wide-ranging species. _Remarks._--The type locality of _G. aquilonaris_ is the small village of Barranca at the bottom of the valley of the Río Urique, several miles south and west of the continental divide. The Urique Valley, known as the Barranca del Cobre in the region south of Creel, is a deep canyon, the walls of which slope abruptly from approximately 7300 to 3000 feet and are dissected by deep side-canyons. Coniferous forest on the upper rim of the canyon is replaced by scrub vegetation on the rocky walls and by an arid tropical flora on the bottom. Maguarachic (elevation approximately 5400 feet, longitude and latitude respectively, 108 degrees, 03 minutes W and 27 degrees, 50 minutes N) and Mojarachic (elevation approximately 7000 feet, longitude and latitude respectively, 108 degrees W and 27 degrees, 52 minutes N) are situated approximately three miles from each other and approximately 27 miles northwest of Creel. Maguarachic is given as "Mafuarachic" on the American Geographical Society map (NG 12, Baja California-Mexico, Prov. Ed., 1924). Mojarachic is not on any map of Chihuahua that I have examined.