Differs from _E. panamintinus_, in base of keel proportionally shorter, angle formed by tip and shaft smaller; from _E. umbrinus_ and _E. palmeri_, in keel higher, angle formed by tip and shaft smaller, distal 2/3 (not 1/2) of shaft markedly laterally compressed, base markedly wider; from _E. bulleri_, in keel smaller, shaft shorter, tip proportionally longer, ridges on either side of tip distinct. For comparisons with all other species of chipmunks of western North America, see the accounts of those species. The baculum in _E. speciosus frater_ is approximately the same size as in _E. umbrinus inyoensis_, but differs in shape as described above. _Specimens examined_: 6. _E. speciosus frater_: California: _Madera Co._: San Joaquin River, near head of N fork, Sierra Nevada Mountains, 2 (BS). _E. speciosus sequoiensis_: California: _Tulare Co._: Mount Whitney, 1 (BS); Sequoia National Park, 2 (BS). _E. speciosus callipeplus_: California: _Kern Co._: Mount Pinos, 1 (BS). #Eutamias panamintinus# (Merriam) Figure 16 Dorsal dark stripes reddish; size small to medium; skull of medium size; braincase flattened. Baculum: Shaft thick; keel low, 1/3 of length of tip; base of keel 1/2 of length of tip; tip 52 per cent of length of shaft; angle formed by tip and shaft 110°; distal 2/3 of shaft moderately compressed laterally; base markedly widened; shaft short, 2.17 mm. Differs from _E. umbrinus_ and _E. palmeri_, in distal 2/3 (rather than 1/2) of shaft moderately compressed laterally; from _E. bulleri_, in keel smaller, shaft shorter, ridges on either side of tip distinct. For comparisons with other species of chipmunks of western North America, see the accounts of those species. The structure of the baculum most closely resembles that of _E. speciosus_ and the geographic ranges of these two species are in juxtaposition. _Specimen examined_: One from Coal Kilns, Panamint Mountains, Inyo Co., California (CN). #Eutamias umbrinus# (J. A. Allen) Figures 17-18 General tone of upper parts dark; size medium to large; skull of medium size; braincase narrowed. Baculum: Shaft thick; keel low, 1/4 of length of tip; tip 36 to 50 per cent of length of shaft; angle formed by tip and shaft 100°; distal 1/2 of shaft markedly compressed laterally; base markedly widened; shaft short to medium, 2.51 to 3.03 mm. Differs from _E. bulleri_, in shaft shorter, keel smaller, ridges on either side of tip distinct; distal 1/2 of shaft strongly compressed laterally. Does not differ from _E. palmeri_. For comparisons with all other species of chipmunks of western North America, see the accounts of those species.