The zoning arrangement of the Bridger Middle Eocene as defined by W.D. Matthew in his 1909 monograph on the Carnivora and Insectivora of the Bridger Basin included a series of stratigraphic units lettered from A to E. The type section is in the western part of the basin but correlation of the sequence in the eastern part of the basin erred in that a very large area shown by Matthew as C, or upper Bridger, is actually B, or lower Bridger. As a consequence many of the mammalian remains collected in the eastern part of the basin were attributed to the wrong horizon. This was discovered in my faunal studies and verified by Wilmot Bradley's mapping of the Sage Creek White Layer, which is the base of Bridger C or upper Bridger. A faunal list of the Mammalia recognized in the Bridger is given with type localities and their horizons, so far as known, and the number of specimens in the National Museum of Natural History collections from each of the two divisions, lower and upper. Following this a discussion of species is given in which the evidence for any species being restricted to one or the other of the stratigraphic divisions is cited, or such information demonstrating its occurrence in both levels, if this is not indicated by the National Museum of Natural History collections (under the catalog numbers of the old United States National Museum). The Annotated Bibliography includes references to all papers in which recognized new mammalian families, genera, and species included in the Bridger faunas are described. Also included are papers in which stratigraphic and additional or detailed information on Bridger mammals is provided, with notations as to extent of coverage, and possible errors of detail or interpretation in certain cases.