Protostephanus is an extinct genus of crown wasp in the Hymenoptera family Stephanidae known from an Eocene fossil found in the United States of America.

[2] The specimen is composed of a partially complete adult female[3] crown wasp that has been preserved as a compression fossil in shale of fine volcanic ash from the Florissant Formation in Colorado.

Cockerell's 1906 type description of the new genus and species was published in the journal Bulletin of the Museum of Comparative Zoology at Harvard College.

The specific epithet ashmeadi was coined in honor of William Harris Ashmead whose entomology works were referenced by Cockerell to determine the affinities of the insect.

The hind legs show a typical crown wasp structure, having an inflated tibia, and a lengthened tarsus that is divided into three segments.