The specimens from scattered localities in the Transition Life-zone of northwestern Colorado and southern Wyoming are larger than _nevadensis_ is elsewhere, and also in certain other features resemble _longicauda_ of the plains to the eastward. Everything considered, the animals in question are much more like _nevadensis_ than _longicauda_. Study of more specimens, especially from Wyoming, might provide grounds for recognizing as a different subspecies the animals in this large area comprising parts of Colorado and Wyoming from which so few specimens now are available. Possibly the name _Putorius culbertsoni_ Coues would apply. Decision on that point will require adequate material from the type locality, Fort Laramie. See discussion of this name under _M. f. longicauda_. In southeastern Idaho males are larger than they are at most other places within the range of _nevadensis_. An average of 7 adults and subadults from Pegram, Montpelier, Springfield, and the vicinity of Pocatello, reveals, when compared with the average of _nevadensis_ from Colorado and that of _longicauda_ from the Great Plains, that this population from southeastern Idaho is nearest to _longicauda_ in linear measurements of the orbitonasal length, mastoid breadth, length of tympanic bullae, and as expressed in percentage of the basilar length, length of tooth-row, breadth of rostrum, and zygomatic breadth. In all other points of size, relative proportions and color, the animals approach nearer to, or actually agree with, _nevadensis_. The specimens commented upon clearly show intergradation between _nevadensis_ and _longicauda_. Similarly, the specimens from Scottsbluff County, Nebraska, here referred to _M. f. alleni_, by their larger size suggest intergradation of that subspecies with the larger _nevadensis-longicauda_ stock although the approach is more toward _longicauda_ than _nevadensis_. Between _oribasus_ and _nevadensis_, however, there is no lack of material showing intergradation. As set forth in the account of _oribasus_, specimens from Montana are truly intermediate structurally as well as geographically.