Stauroneis phoenicenteron has smaller valves than S. rex (26-35 µm wide by 129-199 µm long) and a higher stria density (15-18 in 10 µm). It is likely that S. rex has been misidentified as S. phoenicenteron in U.S. surveys. Stauroneis terryi has septa and pseudosepta. Stauroneis baileyi, reported from Connecticut, has rhombic-lanceolate valves with narrower, more attenuated ends.