From _E. u. sedulus_, the subspecies from the Henry Mountains of Utah, _E. u. montanus_ differs in: Sides darker; general tone of upper parts darker. From _E. u. fremonti_, the subspecies from the mountains of western and northwestern Wyoming, _E. u. montanus_ differs in: General tone of upper parts lighter; hairs around outermost edge of tail tawnier. _Remarks._--Howell (1929:83) stated that the specimens of _E. quadrivittatus quadrivittatus_ (= _E. umbrinus montanus_) from Estes Park, Long's Peak, and Gold Hill, all in Colorado, "average somewhat darker on the back and sides than typical _quadrivittatus_; the light dorsal stripes are also somewhat duller and the dark stripes less blackish, thus showing an approach to the characters of _umbrinus_." Now there are more specimens of _E. u. montanus_ from the mountains of north-central Colorado than were available to Howell. He was not aware of the striking difference between the bacula of _E. quadrivittatus_ and _E. umbrinus_, and the constancy of this difference between all the subspecies of one species and those of the other. Although the geographic range of _E. u. umbrinus_ is closer to the ranges of _E. u. fremonti_ and _E. u. montanus_ than to the geographic range of _E. u. adsitus_, _E. u. umbrinus_ seems to be more closely related to _E. u. adsitus_ than to _E. u. fremonti_ or _E. u. montanus_. This observation may be explained by the presence of continuous habitat for _E. umbrinus_ between the ranges of _E. u. umbrinus_ and _E. u. adsitus_, whereas _E. u. fremonti_ and _E. u. montanus_ are each separated from _E. u. umbrinus_ by areas unsuitable for occupancy by _E. umbrinus_. It must be noted, however, that no actual intergrades between _E. u. umbrinus_ and _E. u. adsitus_ are known. _Specimens examined._--Total number, 36. =Wyoming=: _Albany Co._: 3 mi. ESE Brown's Peak, 10,000 ft., 2; 3-1/2 mi. S Wood's Landing, 1. =Utah=: _Uintah Co._: PR Springs, 7,950 ft., 43 mi. S Ouray, Uintah-Grand county line, 1 UU. =Colorado=: _Jackson Co._: Mount Zirkel, 10,000 ft., on trail, 2 WC; Buffalo Pass, 10,380 ft., 1 WC; Buffalo Pass road, 10,130 ft., 1 WC. _Larimer Co._: 2 mi. E Log Cabin, 7,450 ft., 1 WC; Estes Park, 7,600 ft., 1; 1-1/2 mi. SW Estes Park, 1; 2-1/2 mi. SW Estes Park, 2; 3-1/2 mi. SW Estes Park, 1; 12 mi. SW Estes Park, 1. _Rio Blanco Co._: 1 mi. NW Pagoda Peak, 10,400 ft., 1. _Boulder Co._: Long's Peak, 7 BS; 1 mi. NE Ward, 10,000 ft., 1; 3 mi. S Ward, 9,000 ft., 5; 1/2 mi. E and 3 mi. S Ward, 9,400 ft., 1; 1 mi. S Gold Hill, 8,200 ft., 1. _Clear Creek Co._: Davidson Mine, 3 mi. SW Idaho Springs, 1; Georgetown, 1 CM. _Jefferson Co._: Silver Plume, 1 CM. _Park Co._: Tarryall Creek Camp, 8,700 ft., 1 WC. _Gunnison Co._: S side Crested Butte Mountain, 9,500 ft., 1 WC; mouth of Virginia Basin, Gothic, 1 FC. DISCUSSION