End few cells tapered, usually with a calyptra (cap) on the terminal cell, weakly constricted at crosswalls, without aerotopes.
Filaments thin, not tapered, sheaths fine, cells usually much longer than wide, obvious constrictions between crosswalls (often with an a...
Sheath fine, end not tapered, calyptra (cap) absent from terminal cell, constrictions between crosswalls weak, without aerotopes.