A small but interesting mammalian fauna has been obtained from the Mejocote Valley in the vicinity of Gracias, Honduras, from a series of beds of sand, clay, and volcanic ash, a formation to which the name Gracias is given. The fauna, which consists of Amphicyon, Pliohippus, Neohipparion, Procamelus, Blickotherium, and an indeterminate cervid, appears to be lower Pliocene in age. Horses are the most important element, and it is mainly on the basis of these forms that the age determination has been made. A small flora, associated with the mammalian fauna, suggests that the animals lived in or on the edge of a subtropical rain forest. The absence of mammals of South American origin strongly suggests that no land connection existed between the two Americas during the lower Pliocene, and the presence of the northern type fauna indicates that no marine portal was present at the isthmus of Tehuantepec during the time of deposition of the Gracias formation.