Most likely, ''Ephemera compar'' is an extinct species of burrowing mayfly in the family

Ephemeridae Ephemeridae is a family of mayflies with about 150 described species found throughout the world except Australia and Oceania. These are generally quite large mayflies (up to 35 mm) with either two or three very long tails. Many species have ...

. It was found in North America. Ephemera compar is known from a single specimen, collected from the "foothills of Colorado" in 1873, but despite intensive surveys of the Colorado mayflies reported in 1984, it has not been rediscovered.

References

Mayflies Articles created by Qbugbot Insects described in 1875 {{mayfly-stub