Morphology and taxonomy of Stephanodiscus vestibulis sp. nov. (Bacillarioph y ta)

A new species Stephanodiscus vestibulis is described from an eutrophic, hardwater habitat in western North America. Under the light microscope it resembles. and has perhaps been confused with, certain other small species of the genus. Structural fea-tures of the valve resolved by SEM, however, show that it is unique. The new species is particularly characterized by arch-like vestibules over the external openings of the marginal strutted processes. Other features include central and marginal strutted pro-cesses with three satellite pores, internally domed criba on the puncta and a single la-biate process