Populations of S. amphicephala from the Northern Rockies (Montana Diatom Collection) overlap in size with S. clandestina, raising the question whether these are indeed two separate taxa. Stauroneis amphicephala is considerably larger than S. reichardtii, which has more linear valves. Stauroneis anceps has narrow, rostrate apices. Valves of S. ancepsfallax have capitate apices and are more lanceolate.