Differs from _E. q. hopiensis_, in baculum larger, angle formed by tip and shaft less distinct; from _E. ruficaudus ruficaudus_, in shaft and tip proportionally shorter; from _E. r. simulans_, in keel proportionally lower, shaft usually shorter and narrower; from _E. cinereicollis_, in shaft shorter, angle formed by tip and shaft larger, ridges on either side of tip more distinct; from _E. quadrimaculatus_, in tip proportionally shorter, shaft shorter; from _E. speciosus_, _E. panamintinus_, _E. umbrinus_, _E. palmeri_, and _E. bulleri_, in base not markedly widened, shaft longer, angle formed by tip and shaft larger. For comparisons with _E. alpinus_, _E. minimus_, _E. townsendii_, _E. sonomae_, _E. amoenus_, _E. dorsalis_, and _E. merriami_, see the accounts of those species. Baculum of _E. q. hopiensis_: Shaft thick; keel proportionally low, 1/3 of length of tip; tip 34 per cent of length of shaft; angle formed by tip and shaft 130°; distal 1/3 of shaft slightly compressed laterally; shaft short, 2.64 mm. in length. Differs from _E. ruficaudus ruficaudus_, _E. r. simulans_, _E. cinereicollis_, and _E. quadrimaculatus_, in being shorter, proportions as in _E. q. quadrivittatus_; from _E. speciosus_, _E. panamintinus_, _E. umbrinus_, _E. palmeri_, and _E. bulleri_, in base not markedly widened, angle formed by tip and shaft larger; from _E. alpinus_, _E. minimus_, _E. townsendii_, _E. sonomae_, _E. amoenus_, _E. dorsalis_, and _E. merriami_, except for smaller size, as in _E. q. quadrivittatus_. Bacula of _E. q. hopiensis_ from northeastern Arizona are like those in typical _E. q. quadrivittatus_. The specimens from this region, to judge from parts of the animal other than the baculum, are intergrades between _E. q. hopiensis_ and _E. q. quadrivittatus_. Specimens from near Moab, Grand Co., Utah, are typical _E. q. hopiensis_ and the bacula of these specimens are considerably smaller than those of specimens of typical _E. q. quadrivittatus_. No bacula are known to me that are structurally intermediate between those of _E. q. quadrivittatus_ and _E. q. hopiensis_. _Specimens examined_: 21. _E. quadrivittatus quadrivittatus_: Colorado: _Gunnison Co._: Sapinero, 1 (BS). _Chaffee Co._: Unspecified, 1 (MM). _Saguache Co._: 5 mi. N and 22 mi. W Saguache, 10,000 ft., 1. _Fremont Co._: Canon City, 3 (BS). New Mexico: _Rio Arriba Co._: Dulce, 1 (BS). _Taos Co._: 23 mi. S and 6 mi. E Taos, 8,750 ft., 4. _Union Co._: Sierra Grande, 1 (BS). _Valencia Co._: Mirror Spring, Mt. Taylor, 3 (MM). _Torrance Co._: S end, E slope, Manzano Mountains, 2 (BS). _E. quadrivittatus hopiensis_: Utah: _Grand Co._: Mouth of Nigger Bill Canyon, E side Colorado River, 4 mi. N Moab Bridge, 4,500 ft., 1 (UU); Moab, 4,500 ft., 1 (UU). Arizona: _Apache Co._: Tunicha Mountains, 1 (BS). #Eutamias ruficaudus# Howell Figures 11-12 General tone of upper parts dark tawny; size medium; braincase narrowed.