The smaller, inland variant seems to agree in size, cranial characters, and coloration with _M. f. nigriauris_ to the southward of San Francisco Bay, but lacks the black on the head which characterizes _nigriauris_. The larger variant, on which the description here used for _munda_ is based, comprises animals which differ from _nigriauris_ in larger size, darker color, reduced white facial markings, and larger, relatively wider skull. Both of the variants mentioned above are sharply distinct from _nigriauris_ on the basis of coloration of the inside of the ear which is blackish in nigriauris like the dark facial markings, and in _munda_ is colored like the back. _M. f. munda_ lacks the dark facial markings; an occasional specimen has at most, a trace of the markings but this does not extend back so far as the ears. This difference, blackish versus non-blackish face, persists eastward of San Francisco Bay to at least as far as the Carquinez Straits, where a specimen of _munda_ is available from 4 miles north of Vallejo and one of _nigriauris_ from Glen Frazer Station on the south shore opposite Vallejo. [Illustration: FIG. 30. Map showing the geographic distribution of subspecies of _Mustela frenata_ in California] Intergradation with _M. f. nevadensis_ and possibly with _M. f. saturata_ is indicated by specimens from South Yolla Bolly Mountain, Trinity County. In them the external measurements and measurements of the skull are intermediate. Also the white frontal spot is much reduced in size. The white bars in front of the ears are absent in three specimens, and weakly developed in the other two. The relative proportions of the skulls as a whole are nearer those of _nevadensis_ or _saturata_ than _munda_. The skull of one of the three adult males and the skull of the adult female suggests _M. f. oregonensis_ in certain features; for example, the dorsal outline of the skull in longitudinal axis is slightly convex as it is in _oregonensis_. None of the specimens shows malformation of the frontal sinuses such as results from infestation by parasites. _Specimens examined._--Total number, 37, arranged by counties from north to south. Unless otherwise indicated specimens are in the Museum of Vertebrate Zoölogy.