Comparisons.—From Eutamias amoenus luteiventris, the only subspecies of that species in Wyoming, E. minimus differs in: Size smaller; tip of baculum in adults less than 28 per cent of length of shaft; zygomatic arches proportionally wider; underparts white or with less yellow or tawny.
From E. umbrinus, E. minimus differs in: Size smaller; general tone of upper parts lighter; base of baculum not widened but almost as narrow as least diameter of shaft.
Fig. 1. Known occurrence and probable geographic distribution of the subspecies of Eutamias minimus in Wyoming. The symbols for locality records are as follows: Circles, specimens reported but not examined; solid circles, precise localities of specimens examined; solid triangles, localities of specimens examined, known only to county.
| 1. E. m. minimus | 4. E. m. confinis |
| 2. E. m. consobrinus | 5. E. m. silvaticus |
| 3. E. m. pallidus | 6. E. m. operarius |
From E. dorsalis utahensis, the only subspecies of this species in Wyoming, E. minimus differs in: Dorsal dark stripes distinct and usually blackish; skull smaller; tip of baculum of adults less than 28 per cent of length of shaft.
Remarks.—This is the smallest of the species of chipmunks in Wyoming, and in the state can be readily distinguished from the other species by the smaller size and by the characteristic proportions of the baculum.
E. minimus occurs in all the Life-zones of Wyoming, and inhabits open country, such as in the great expanses where sagebrush (Artemesia sp.) is predominant, or inhabits the edges of forests, never occurring in the forest proper.
Analyses of measurements of the skull indicate that of the six subspecies of E. minimus that are found in Wyoming, two are small (E. m. minimus and E. m. consobrinus) and the other four are large (E. m. pallidus, E. m. confinis, E. m. silvaticus, and E. m. operarius). Within these size-groups the subspecies can be distinguished by differences in color pattern.