Fig. 1. Dorsal view of skull and a lateral and a medial view of the right lower jaw to show points between which measurements of the skull were taken. × 1¾. Based on Eutamias ruficaudus ruficaudus, from 6 mi. S St. Mary, 6500 ft., Glacier Co., Montana. A to A'—greatest length of skull; B to B'—length of nasals; C to C'—zygomatic breadth; D to D'—least interorbital constriction; E to E'—cranial breadth; F to F'—inner mandibular length; G to G'—condylo-alveolar length of mandible.
A total number of 434 specimens are listed as examined in this study, and additionally, numerous other specimens were superficially examined in the United States Biological Surveys Collection. Bacula of each of the named kinds of chipmunks in this paper, were examined.
Whenever two or more samples are stated to be significantly different, the meaning is that the difference is statistically significant.
The geographic distribution of each subspecies and the localities of specimens or series of specimens are plotted on the map (fig. 2).
When comparisons were made to ascertain specific and subspecific differences, only adults, or animals in which the enamel was worn through on the permanent P4 and p4 were used. Within this age range, only specimens in comparable pelage were used to ascertain differences in color.
Miss Viola S. Schantz of the United States Fish and Wildlife Service, Mr. Alfred Bailey of the Colorado Museum of Natural History, Dr. W. H. Burt of the Museum of Zoology of the University of Michigan, Dr. Stephen D. Durrant of the Museum of Zoology of the University of Utah, Dr. Robert M. Stabler, curator of the Warren Collection of Colorado College, and Mr. James S. Findley, generously loaned specimens for my use. Doctors E. Raymond Hall, Rollin H. Baker, Robert W. Wilson, Keith R. Kelson, E. Lendell Cockrum, and other friends and associates have given valued suggestions and assistance. My wife, Alice M. White, made the illustrations and helped me record and analyze the data.
Assistance with field work is acknowledged from the Kansas University Endowment Association, the National Science Foundation, and the United States Navy, Office of Naval Research, through contract No. NR161 791.