cene deposits is osteologically indistinguishable from living species (Miller, 1965). Plio-pleistocene catostomids (represented mostly by disarticulated incomplete skeletons) have been studied in detail by Smith (1975), Miller and Smith (1981) and others. Little is known, however, about the structure and relationships of Early Coenozoic catostomids. The Eocene-Oligocene catostomid genus Amyzon was first described by Cope (1872) from Oligocene specimens collected in Nevada. Three additional Oligocene Amyzon species have been described from Colorado (Cope, 1884) and two Middle Eocene species from British Columbia (Cope, 1893; Wilson, 1977). A Late Eocene or Early Oligocene Amyzon is known from Oregon (Cavender, 1968). Cavender (1973, at 53rd annual ASIH meeting) first reported the occurrence of a catostomid in the Green River Formation, based on a poorly preserved partial specimen in the United States National Museum (USNM 175357). In this paper we describe Amyzon gosiutensis, n. sp., from the Laney Shale Member of the early Middle Eocene (Bridgerian) Green River Formation of Wyoming. This is the first catostomid described from the Green River For-