_Eutamias panamintinus_, according to Howell (_op. cit._:78) and Johnson (_op. cit._:83), is a near relative of _E. amoenus_. But, the baculum in _E. panamintinus_ more closely resembles that in _E. speciosus_ than that in _E. amoenus_ (compare figs. 5, 15, and 16). Consequently I have placed _E. panamintinus_ in the _speciosus_-group. In north-central Colorado, specimens that really are _E. umbrinus_ (subspecies _montanus_) have, in the past (Howell _op. cit._:82), been referred to _E. quadrivittatus quadrivittatus_, but the bacula of the two species differ markedly from each other (compare figs. 8-9 with 17-18) and permit the specimens readily to be correctly identified to species. Further, Howell (_op. cit._:95) placed _E. umbrinus_ (subspecies _umbrinus_ and _fremonti_ of current usage) in the _quadrivittatus_-group, whereas the structure of the baculum leads me to place _E. umbrinus_ in the _speciosus_-group. Thus, groups of species established on the basis of only skulls and skins, in a few instances differ from those established on a broader basis which includes the bacula. Johnson (_op. cit._:63) writes, "Each species [of Eutamias] has a characteristic habitat which differs from those of other species. Where two or more species occur together in a general locality they are usually mutually exclusive in their choice of foraging and nesting sites and in the time of breeding." Thus he classified the species of Californian chipmunks not only by morphologic characteristics but by habits and habitats as well. The characteristics of the skulls and skins of chipmunks probably reflect the habitats in which these animals live. The characteristics of the bacula, on the other hand, may also reflect the habitats in which the animals live, but to a lesser degree. Because the structures of the bacula are probably less affected by the action of the external environment they probably indicate relationships between groups of species of chipmunks more clearly than do characteristics of the skulls and skins. If the structures of the bacula indicate relationships between groups of species of chipmunks more clearly than do the characteristics of the skulls and skins, the close resemblance of the skulls of _E. quadrivittatus_ and _E. umbrinus_ may be thought of as convergence. The same can be said of _E. amoenus_ and _E. panamintinus_. LITERATURE CITED FRILEY, C. E., JR. 1947. Preparation and preservation of the baculum of mammals. Jour. Mamm., 28:395-397, 1 fig., December 1. HOWELL, A. H. 1929. Revision of the American chipmunks (genera _Tamias_ and _Eutamias_). N. Amer. Fauna, 52:1-157, 10 pls., 9 maps. JOHNSON, D. H. 1943. Systematic review of the chipmunks (genus Eutamias of California). Univ. California Publ. Zool., 48:63-148, 6 pls., 12 figs, in text, December 24. WHITE, J. A. 1951. A practical method for mounting the bacula of small mammals. Jour. Mamm., 32:125, February 15.