This common name refers to only one species.
These are very rarely called Brown Bivisibles.
is generally reported to be the largest North American species of mayfly in angler entomologies, though this understanding is being challenged by reports of Hexagenia limbata
that may exceed 40mm in some locales. Regardless, it is certainly the largest mayfly in the region of its distribution. Sometimes it appears together with species of Hexagenia
, but in other places it creates excellent action on its own.