TWO NEW PLOCENE SPECIES OF CYCLOSTEPHANOS (BACILLARIOPHYCEAE) WITH COMMENTS ON THE CLASSIFICATION OF THE FRESHWATER THALASSIOSIRACEAE 1

Two new species of the diatom genus Cyclostephanos Round are described from Pliocene fossil deposits in western North America. Cyclostephanos undatus is distinguished from other Cyclostephanos species by its tangentially undulate valve face; Cyclostephanos fenestratus is distinguished by its extremely shallow alveoli. This paper records previously unreported morphological detail of Cyclostephanos and speculates that structure of the punctum, labiate process and strutted process may enhance diagnosis of the freshwater genera of the Thalassiosiraceae Lebour emend. Hasle. Cyclostephanos undatus is similar to several Cyclotella species, but its external costae are raised and its alveolar morphology is similar to that of Cyclostephanos dubius (Fricke) Round. Cyclostephanos fenestratus is similar in external view to Stephanodiscus Ehrenb. However, the two species described here have flat cribra covering the mantle puncta and the labiate processes appear to lack external tubes, whereas Stephanodiscus species have domed mantle cribra and external tubes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65645/1/j.1529-8817.1986.tb04154.x.pd

Stephanodiscus dubius (Fricke) Hustedt : Etude en microscopie optique et en microscopie électronique

L'étude en microscopie optique d'échantillons fossiles provenant d'Ethiopie a montré l'existence de deux variétés de Stephanodiscus dubius. Une étude en microscopie électronique a révélé les similitudes de structure entre ce taxon et le genre Cyclotella.Descourtieux-Coqueugniot C. Stephanodiscus dubius (Fricke) Hustedt : Etude en microscopie optique et en microscopie électronique. In: Bulletin mensuel de la Société linnéenne de Lyon, 50ᵉ année, n°8, octobre 1981. pp. 244-249