Key to the species of Harrahium Witenberg, 1926

1a. Rudimentary oral sucker absent; eggs relatively small, 125 µm x 65 µm..................... H. tringae (Brandes, 1892)

1b. Rudimentary oral sucker present; eggs relatively large, 161 µm x 91 µm....................... H. halli (Harrah, 1922)