Key to genera of Discomyzini from the New World

1. A postsutural supra-alar seta much reduced (no larger than surrounding setulae) or absent............................ 2

- A postsutural supra-alar seta present, size subequal to presutural supra-alar seta.................................... 5

2. Pseudopostocellar setae well developed, length about 1/2 that of ocellar setae, orientation divergent at usually less than 90°....................................................................................... Clasiopella Hendel

- Pseudopostocellar setae weakly developed, length considerably less than 1/2 that of ocellar setae, orientation variable...... 3

3. Only the reclinate fronto-orbital seta well developed; face conspicuously and deeply, transversely rugose...................................................................................................... Discomyza Meigen

- At least 1 proclinate fronto-orbital seta in addition to reclinate seta well developed; face usually at most with shallowly impressed, transverse striae.............................................................................. 4

4. Eye appearing bare; 1 well-developed proclinate fronto-orbital seta (2nd seta greatly reduced), inserted anterior to reclinate seta; presutural supra-alar seta weakly developed, length less than anterior notopleural seta (except in M. cressoni Lizarralde de Grosso); legs bicolored.............................................................. Mimapsilopa Cresson

- Eye conspicuously setulose; 2 well-developed proclinate fronto-orbital setae, anterior proclinate seta at about same level as large, reclinate seta, posterior proclinate seta inserted posterior of reclinate seta; presutural supra-alar seta well developed, length longer than anterior notopleural seta; legs unicolorous, blackish brown...................... Helaeomyia Cresson

5. Interfrontal seta present; fronto-orbital setae 4 (anterior 2 setae proclinate, 3rd lateroclinate, 4th lateroreclinate)................................................................................................. Paratissa Coquillett

- Interfrontal seta absent; fronto-orbital setae 2–3.............................................................. 6

6. Supra-alar seta well developed, length subequal to postalar seta; wing usually mostly hyaline, at most with anterior margin faintly infuscate....................................................................... Rhysophora Cresson

- Supra-alar seta moderately well developed, length about half postalar seta; wing usually with at least anterior margin infumate, wing sometimes mostly brown and with white spots............................................ Guttipsilopa Wirth