In all American weasels (subgenus _Mustela_) the color, at least in summer, is brown with more or less white or whitish on the underparts. In one species, _Mustela africana_, there is a longitudinal stripe of brown on the middle of the light-colored underparts; this stripe is absent in each of the other three American species. Two species, _M. erminea_ and _M. frenata_, always have a black tip on the tail. Of the other two species, _M. africana_ lacks the black tip and _M. rixosa_ may or may not have a few black hairs in the tip of its tail. White or light yellowish facial markings occur in subspecies of _M. frenata_ from the southwestern United Stated to Central America. Subspecies having the most extensive light-colored facial markings have the remainder of the upper part of the head black. In weasels without light facial markings the upper parts of the head all are brown. In the two species, _M. erminea_ and _M. frenata_, the extent to which the light color of the underparts extends down the insides of the legs and out on the underside of the tail, or the absence of light color on these parts, is a matter of geographic variation. The same can be said for _M. rixosa_ except that first its tail is unicolored and second individual variation as well as geographic variation accounts for the color pattern on the underparts and legs in animals from the southeastern part of the range of the species. The most remarkable feature of the coloration of weasels is the winter whitening. This occurs in the northern part of North America in each of the three species of weasels found on that continent. The black tip of the tail in _M. erminea_ and _M. frenata_ remains black in winter. If an individual of _M. rixosa_ has black hairs on the tip of its tail in summer, there are thought to be black hairs there also in winter. Otherwise the winter pelage is all white in northern areas in each of the three species. In this white winter coat the animal is known as ermine.