_Mustela frenata primulina_ is closely related to _M. f. noveboracensis_, from which, on the average, it differs in the lighter color of the upper parts of the summer coat, in the more intense coloring of the underparts, and in certain cranial features pointed out above. In the southern part of its range, however, _noveboracensis_ has the underparts only a little less intensely colored with yellow than _primulina_. Also, the skull of the one topotype from 7-1/2 miles southeast of Carthage, a subadult male in brown, winter pelage, is almost exactly intermediate between that of _noveboracensis_ from Massachusetts and _primulina_ of Douglas County, Kansas, and Boone County, Arkansas. _M. f. primulina_ often has the underparts white in winter, as does this topotype which agrees with the average of _noveboracensis_ in small size of teeth and narrowness across the mastoid processes and zygomatic arches. However, it agrees with _primulina_ in shape and relative size of the rostrum. It is almost exactly intermediate in shape and width of the tympanic bullae. Three other males, but no females, all in winter pelage, are available from eastern Missouri. Of the two from Silex, Lincoln County, one is nearer _noveboracensis_ and the other nearer _primulina_ on the basis of cranial characters. The third specimen, from four miles south of Lesterville, so far as I can determine by examination of individual cranial characters and tabulation of results, is exactly intermediate. Final decision on the proper allocation of specimens from the parts of Missouri represented can best be made when skulls of females are available. From the fact that the skull of the female referred to _noveboracensis_ from Golconda, Illinois, shows almost as many characters of _primulina_ as of _noveboracensis_, it is judged that females from as far west as Silex and Lesterville, Missouri, will show even more characters of _primulina_ and so be referable to that form. If this supposition be correct, the present reference of the almost exactly intermediate males, from eastern Missouri, will stand; otherwise, it may not.