During the past five years, renewed prospecting and collecting of mammalian fossils in the Florissant Formation within Florissant Fossil Beds National Monument in central Colorado has nearly tripled the known diversity of fossil mammals from this rock unit. Taxa first recorded here from the Florissant Formation include the eomyid rodent Paradjidaumo trilophus , the lagomorph Palaeolagus , and the rare artiodactyl Pseudoprotoceras longinaris . We also describe an isolated deciduous premolar of a protoceratid. We update the mammalian faunal list of the Florissant Formation, which includes some 16 species in 13 families and 6 orders. The mammalian fauna corroborates the Chadronian (latest Eocene) age determined by others. Geographic ranges of Pelycomys , Palaeolagus , and Paradjidaumo trilophus are extended slightly southwest from northeastern Colorado, and the range of Pseudoprotoceras longinaris is extended southwest from Wyoming and Nebraska. Based upon comparison with nearest living relatives and plausible analogs, the mammalian taxa represented in the Florissant Formation seem to be consistent with the moist, warm temperate, relatively high elevation wetland and woodland habitats that have been inferred by others for the area in and around late Eocene Lake Florissant.