Premise of research. Leaves of an extinct kind of cycad are recognized from the middle and late Eocene Clarno Formation of Oregon. Although the pinnately compound leaf is similar in gross form and organization to some other extant and Cenozoic cycads such as Dioon Lindl., Encephalartos Lehm., and Dioonopsis Horiuchi et Kimura, it is readily distinguished from them by its venation, consisting of a closed reticulum of a single order of veins with a frequent dichotomizing and anastomosing pattern.Methodology. Fossils stored in the Museum of Paleontology (University of California), Florida Museum of Natural History (University of Florida), and Condon Museum of Natural History (University of Oregon) were studied applying conventional macromorphological and micromorphological methods including transmitted light and epifluorescence microscopy.Pivotal results. The leaves conform in their peculiar venation and epidermal anatomy to the extinct genus Ctenis Lindley et Hutton, which previously was known only from Mes...