Differs from _E. speciosus_, _E. panamintinus_, _E. umbrinus_, _E. palmeri_, and _E. bulleri_, in base not widened, shaft thinner; from _E. quadrivittatus_, _E. ruficaudus_, _E. cinereicollis_, and _E. quadrimaculatus_, in shaft thinner, baculum usually shorter; from _E. merriami_, in shaft markedly shorter, base not incised dorsally, tip proportionally longer. For comparisons with _E. alpinus_, _E. minimus_, _E. townsendii_, _E. sonomae_, and _E. amoenus_, see the accounts of those species. _Specimens examined_: 12. _E. dorsalis dorsalis_: Arizona: _Yavapai Co._: 3 mi. N Ft. Whipple, 5,000 ft., 1 (BS). _Gila Co._: Carr's Ranch, Sierra Ancha Mountains, 1 (BS). _Pima Co._: Unspecified, 1 (MM). New Mexico: _Valencia Co._: Mount Taylor, 1 (MM); 1 mi. N Cebolleta, 1 (MM). _Socorro Co._: San Mateo Mountains, 1 (BS). _Chihuahua_: Sierra Madre, near Guadalupe y Calvo, 3 (BS). _E. d. utahensis_: Wyoming: _Sweetwater Co._: W side Green River, 1 mi. N Utah Border, 1. Colorado: _Moffat Co._: Escalante Hills, 20 mi. SE Ladore, 1 (BS). Arizona: _Coconino Co._: Ryan, 1 (BS). #Eutamias merriami# (J. A. Allen) Figure 7 General tone of upper parts grayish; cheeks and underparts white, more or less dulled by gray; size large; skull large. Baculum: Shaft thin; keel low, 2/5 of length of tip; tip 16 per cent of length of shaft; angle formed by tip and shaft 130°; distal 1/10 of shaft slightly compressed laterally; base incised dorsally; shaft markedly long, 4.88 mm. Differs from _E. speciosus_, _E. panamintinus_, _E. umbrinus_, _E. palmeri_, and _E. bulleri_, in base incised dorsally, base not widened, shaft thinner, tip proportionally shorter; from _E. quadrivittatus_, _E. ruficaudus_, _E. cinereicollis_, and _E. quadrimaculatus_, in base incised dorsally, shaft thinner, tip proportionally much shorter. For comparisons with _E. alpinus_, _E. minimus_, _E. townsendii_, _E. sonomae_, _E. amoenus_, and _E. dorsalis_, see the accounts of those species. _Specimens examined_: One from Mount Piños, Ventura Co., California (LA). #Eutamias quadrivittatus# (Say) Figures 8-10 Color bright and tawny; size medium to large; braincase widened. Baculum of _E. q. quadrivittatus_: Shaft thick; keel proportionally low, 1/4 of length of tip; tip 30 to 44 per cent of length of shaft; angle formed by tip and shaft 130°; distal 1/3 of shaft slightly compressed laterally; shaft long, 3.17 to 3.62 mm.