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.
Additional intergrades with noveboracensis are available from eastern Iowa. Of five specimens from Hillsboro, Iowa, two males and a female have tympanic bullae like those of primulina but the other two males have bullae like those of noveboracensis. The female is smaller than primulina and in this small size and in general configuration of the skull, viewed dorsally, is more nearly like noveboracensis. As a whole, the population averages almost exactly intermediate. The same is true of 3 males and one female from Muscatine. The subadult male from Keosaqua, to my eye, resembles noveboracensis in the greater length of the skull anteriorly to the postorbital processes, and in the relative narrowness across the mastoidal region, but otherwise is more like that of primulina. Two males and one female from Tipton, although in each instance variously intermediate, are as a whole nearer primulina, No. 2865, Coe College, male adult, from Cedar Rapids, has characters of the three races, spadix, noveboracensis and primulina. In the skull, the width suggests spadix, the narrow mastoid region, noveboracensis, and the tympanic bullae are as in spadix or primulina. One male, no. 12, Coe College, from Dubuque, is as narrow across the mastoid region as is noveboracensis although the bullae are well inflated as in primulina. The skull, without corresponding skin, of a female, no. 140a, Iowa State College, from Green's Island, also resembles noveboracensis in narrowness of the mastoidal region, and in small size of skull, but in larger teeth, broader tympanic bullae, and sagittal crest is referable to primulina. Of two females from Vinton, one adult is typical of primulina but the other, a subadult, is practically indistinguishable from female noveboracensis, from Ann Arbor, Michigan. Three males from Vinton agree well with primulina except that the interorbital region is wider than average and thereby suggests spadix or noveboracensis. An adult female from New Hartford also is typical of primulina except for the broader interorbital region. Three males from Fayette are typical of primulina.
Other specimens from Iowa are intergrades with spadix, or if not with spadix, with the animal of northwestern Iowa which in some ways combines the characters of longicauda and spadix. For example, no. 2665, Coe College, an adult male from Davenport, has the anterior part of the skull (all that is preserved) heavily ridged as in spadix and in addition, the underparts are marked with the shade of reddish displayed by topotypes of spadix and with some yellowish as seen in longicauda. The color pattern, however, is as in primulina. A young male, no. C-51, Iowa State College, from Kelley, Story County, has anteriorly truncate bullae as are more frequently found in the longicauda-spadix stock of northwestern Iowa, than in primulina. In other respects, the animal, in so far as can be judged from the broken skull, agrees with primulina as it certainly does in color, color pattern, and external measurements. An adult male, no. 499a, Iowa State College, from 2 miles east of Ledges St. Park, in Boone County, in short body, size of teeth, and size of skull, in so far as the broken parts can be measured, resembles primulina more closely than it does any other subspecies. The long tail, long hind foot, wide extent of the light-colored underparts, and extension of the color of the underparts onto the hind feet are more as in spadix. Other intergrades with spadix from Iowa are mentioned in the account of spadix.
The specimen from Swartz, Louisiana, suggests intergradation with arthuri in that the anteromedial part of the tympanic bulla is less inflated than in typical primulina.
Intergrades with longicauda are available from Riley and Pratt counties, Kansas. No. 7182, Univ. Kans., subadult male in winter pelage, from near Winkler, has a skull of larger size as in longicauda with which race it seems to agree in large size of body, tail and hind foot, although the collector's measurements are lacking. Color pattern and relative proportions of the skull throughout are as in primulina. The young male, no. 3495, Univ. Kans., from Pratt, Kansas, agrees in external measurements and large size of skull with longicauda, but has the color and color pattern precisely as in primulina. The teeth are smaller as in primulina. Immaturity prevents judging of its relationships on the basis of relative proportions of the skull.
The two specimens, skins only, available from Oklahoma, are provisionally referred to primulina. These are remarkable for the restriction of the color of the underparts and for the intensity of the yellow coloration of the underparts. The specimen from Norman has the color of the underparts entirely absent from the hind legs and not extending posteriorly to the penis. On the chest and lower throat, large spots of color of the upper parts are present and the yellow area of the underparts on the belly is narrower than in any other specimen of primulina examined. The specimen from 8 miles northwest of Stillwater has the color of the underparts only a little less restricted although this color does extend over the inguinal region almost to the knees. The skin of the posterior part of the body of a weasel is available from 10 miles south of Sulphur Springs, Texas. It, likewise, is only provisionally referred to primulina. The coloration is about as in the specimens from Oklahoma but the distribution of the color of the underparts cannot be made out.