21. Mandibles, long palpi and ligula present; size very small .......... Fam. 47. Micropterygidae, see p. [435].
22. Hind wing with not more than 8 nervules (Cat. 23-58).
23. Hind wing with nervule 8 remote from 7 after origin of nervules 6 and 7 (Cat. 24-51).
24. Frenulum absent (Cat. 25-29).
25. Hind wing with one internal nervure; nervule 8 with a precostal spur .......... Fam. 31. Pterothysanidae, see p. [406].
26. Hind wing with two internal nervures (Cat. 27 and 28).
27. Hind wing with a bar between nervules 7 and 8 near the base; nervure 1a directed to middle of inner margin .......... Fam. 30. Endromidae, see p. [406].
28. Hind wing with no bar between nervules 7 and 8; nervure 1a directed to anal angle .......... Fam. 29. Lasiocampidae, see p. [405].
29. Hind wing with three internal nervures .......... Fam. 21. Arbelidae, see p. [396].
30. Frenulum present (Cat. 31-51).