| Olcella parva (Adams, 1904) |
| Olcella projecta (Malloch, 1913) |
| Olcella punctifrons (Becker, 1912) |
| Olcella trigramma (Loew, 1863) |
| Onychaspidium Enderlein, 1911 |
| Onychaspidium apicale (Williston, 1896) |
| Onychaspidium quadridentata (Duda, 1930) |
| Opetiophora Loew, 1872 |
| Opetiophora straminea Loew, 1872 |
| Oscinella Becker, 1909 |
| Oscinella bracata (Duda, 1930) |
| Oscinella dampfi Aldrich, 1929 |
| Oscinella frit (Linnaeus, 1758) |
| Oscinellinae Becker, 1910 |
| Palaeoconioscinella Duda, 1930 |
| Palaeoenderleiniella Duda, 1930 |
| Parectecephala Becker, 1910 |
| Parectecephala maculosa (Loew, 1872) |
| Pseudochlorops Malloch, 1914 |
| Pseudogaurax Malloch, 1915 |