Abstract

Light and scanning electron microscopic observations on a new species of Adoneis, A. miocenica, from Miocene sediments off the coast of Chile are presented. The new species differs from the only previously described species of Adoneis by having a ring of rimoportulae around the valve in addition to one rimopor-tula at each apex. Valve shape, velum structure and presence of a central sternum suggest a systematic placement within the Rhaphoneidaceae, and the genus is similar to many other species assigned to the araphid diatoms. The unique combination of centric and pennate features found in A. miocenica is discussed relative to whether the araphid diatoms are a natural group.