Eighteen perissodactyl taxa have been identified in the Field Museum collections from the Washakie Formation, Washakie Basin, Wyoming: Orohippus sp., Epihippus gracilis, Telmatherium sp., Mesatirhinus sp., Metarhinus sp., Dolichorhinus sp., Brontotherioidea indeterminate, Isectolophus latidens, Eomoropus amarorum, Helaletes nanus, Dilophodon minusculus, Hyrachyus modestus, Hyrachyus eximius, Triplopus cubitalis, Triplopus implicatus, cf. Forstercooperia minuta, Hyracodontidae indeterminate, and Amynodon advenus. At present, the Washakie Formation is divided into two members: the lower Kinney Rim Member and the upper Adobe Town Member. The Adobe Town Member is informally divided into lower, middle, and upper units, with the Bridgerian-Uintan North American Land Mammal "Age" boundary currently placed between the lower and middle units. -- The Kinney Rim Member contains Mesatirhinus sp., Helaletes nanus, Hyrachyus modestus, and Hyrachyus eximius. Helaletes nanus and Hyrachyus modestus occur throughout the Bridgerian, and their usefulness in defining finer temporal divisions is thus limited. Hyrachyus eximius elsewhere is limited in age to the late Bridgerian. Its occurrence near the base of the Kinney Rim Member indicates the lack of early Bridgerian age sediments in the Washakie Formation. Telmatherium sp., Mesatirhinus sp., Isectolophus latidens, Hyrachyus modestus, and Hyrachyus eximius are present in the lower unit of the Adobe Town Member, also considered to be late Bridgerian in age. Metarhinus sp., Dolichorhinus sp., Eomoropus amarorum, Dilophodon minusculus, Triplopus cubitalis, Triplopus implicatus, cf. Forstercooperia minuta, and Amynodon advenus occur only in the middle unit of the Adobe Town Member. All these taxa have early Uintan first occurrences except Dilophodon minusculus and Hyrachyus eximius, which have late Bridgerian first occurrences, and Amynodon advenus, which has an earliest Uintan first occurrence. Additionally, Dilophodon minusculus and Hyrachyus eximius are known from earliest Uintan deposits elsewhere. This apparent overlap of late Bridgerian taxa with early Uintan taxa in the middle unit of the Adobe Town Member indicates that the Shoshonian Subage of the Uintan North American Land Mammal "Age" may be present within the middle unit of the Adobe Town Member in addition to the lower unit, as previously suggested by Flynn (1986). The presence of the Uintan taxon Epihippus gracilis from the upper unit of the Adobe Town Member indicates only an undifferentiated Uintan age. Among perissodactyls, the future discovery of Colodon or Epitriplopus (both late Uintan first appearance taxa) from the upper unit of the Adobe Town Member would indicate the presence of the early-late Uintan boundary within the Washakie Formation Includes bibliographical references (p. 35-37) Fieldiana series has been published as Geological Series by Field Columbian Museum (1895-1909) and Field Museum of Natural History (1909-1943), and as Fieldiana: Geology by Chicago Natural History Museum (1945-1966) and Field Museum of Natural History (1966-1978). Fieldiana Geology New Series No. 1 began June 29, 1979