_Remarks._--The smallest males of the entire species are of this subspecies and the females of it are barely larger than those of _olympica_ and _gulosa_ and hence are among the three smallest. The material now available consists only of one or a few specimens from each of several widely separated localities. If as many specimens per unit area were available as there are of the species _M. erminea_ from southern British Columbia, geographic variation warranting the division of _muricus_ into more than one subspecies might be revealed. Evidence pointing in this direction is comprised in the pale color and small size of the pair of adults from Wheeler Peak on the eastern border of Nevada; the suggestion is that there is a distinct pale race of small individuals in the isolated spots of boreal life-zone in the mountains of the desert. The color and size of the specimens from the Toyabe Mountains, and that from the Pine Forest Mountains, both places also in Nevada, nevertheless, lend no support to this suggestion. Comparison of specimens from the Rocky Mountains of Colorado with those from the Sierra Nevada of California gives no basis for recognizing more than one subspecies. Therefore, _Putorius streatori leptus_ Merriam with type locality at Silverton, San Juan County, Colorado, falls as a synonym of the earlier named _Putorius (Arctogale) muricus_ Bangs with type locality at Echo, El Dorado County, California. Furthermore, specimens from northern New Mexico, the southernmost known area of occurrence for the subspecies (and for the species), are as large as specimens from far north in the range of the subspecies, say, in northwestern Wyoming; there is therefore no evidence of progressive decrease in size to the southward as in advance of study I supposed existed in _muricus_. This erroneous supposition was held because I knew that there was a decrease in size to the southward in the species as a whole and also in each of the subspecies _richardsonii_ and _invicta_ directly to the north of _muricus_. Intergradation with _invicta_ is shown by specimens from southwestern Montana. Where the margins of the geographic ranges of _invicta_ and _muricus_ approach one another elsewhere, low-lying territory, zonally unsuited to the existence of the species, occurs along the Snake and Columbia rivers, and precludes any chance of intergradation except around the head of the Snake River Plains. Two specimens, here referred to _muricus_, from Siskiyou County, California, in both color and cranial characters, are intergrades with _streatori_ and might be referred with almost equal propriety to _streatori_. _Specimens examined._--Total number, 52, arranged alphabetically by states, then by counties from north to south within each state. Unless otherwise indicated, specimens are in the Museum of Vertebrate Zoölogy, University of California at Berkeley.