The ranges as now known of three subspecies of _Mustela frenata_ approach near to Fort Laramie. These are _M. f. longicauda_, _M. f. alleni_, and _M. f. nevadensis_. The skull of the type of _culbertsoni_ is not typical of any one of the three mentioned races. The small size of its teeth and relative (to basilar length) shallowness of the frontal region of the skull through the postorbital processes of the frontal are as in _nevadensis_. The zygomatic arches are not so greatly expanded as in some specimens of _longicauda_ and are more like the average for _nevadensis_ or _alleni_, as also is the relatively (to basilar length) long orbitonasal length. However, each of these characters is subject to variation and alone is not surely diagnostic, especially toward the margin of the range of any one of the subspecies concerned. The same may be said of the relatively great breadth of the skull interorbitally--a feature typically found in _longicauda_. More important, in my estimation, is the large size of the skull; all parts measured (excepting the teeth, the depth at the posterior border of the last upper molars, the zygomatic breadth, and the depth of the tympanic bullae) equal or approach nearest to the average for males of _longicauda_ of similar age. The small size of _alleni_ prevents its identification with _culbertsoni_. The question of application lies between _nevadensis_ and _longicauda_. If the long-tailed weasel at Fort Laramie is found to be referable to the race earlier named _longicauda_, no change in current nomenclature will be effected. If, on the other hand, the long-tailed weasel from Fort Laramie is found to be referable to _nevadensis_ this name will have to fall before the earlier proposed name _culbertsoni_. There is, however, a third possibility, namely, that the long-tailed weasel of the Transition and Upper Sonoran zones of southern Wyoming and northern Colorado, as for example, at Lay, Colorado, may represent a recognizable race characterized by size about as in _longicauda_, relative proportions of skull about as in _nevadensis_ and coloration intermediate, to which the name _culbertsoni_ may apply. For more detailed discussion of this possibility, see remarks under _M. f. nevadensis_. Satisfactory application of the name _Putorius culbertsoni_ Coues requires an adequate series of adult specimens, of both sexes in the summer coat with external measurements taken in the flesh, from the type locality and like material from elsewhere in southern Wyoming. On the evidence furnished by the skull of the type of _culbertsoni_, that name tentatively is placed in the synonomy of _longicauda_. Only 2 of 25 adults examined for malformation of the frontal sinuses by parasites showed evidence of disease.