Fine structures of Stephanodiscus excentricus Hust. and S. niagarae Ehrenb. from Terrebonne diatomite, Oregon, USA

Abstract

The fine structures of Stephanodiscus excentricus Hust. and S. niagarae Ehrenb. were studied in detail using materials taken from Pleistocene diatomite, Terrebonne, Oregon, USA. The Terrebonne diatomite is the type locality of S. excentricus which is known for the unique characteristic of its valve pattern center which is not located at its geometric valve center. External and internal views of the two Stephanodiscus taxa using SEM and LM photographs show the location and shape of mantle fultoportulae and rimoportulae, as well as fascicles made up of areolae rows.