Couplet 31

31a:  Head with short but distinct temple behind eye, set off from narrowed neck; apex of mandible bidentate; ligula with a single lobe; mesonotum with stridulatory file.

Megalopodidae  p. 445

31b:  Head lacking temples, evenly narrowed from behind eyes to neck; apex of mandible unidentate or bidentate; ligula lobed; mesonotum without stridulatory file.