Key to species of S. signatus species-group from Vietnam and China

1 Pterostigma elongate, about 0.33 as long as cell r1, not filling entire apex of cell R1; R4+5 and M1 distinctly convergent apically; thorax brownish yellow................................................................................ 2

- Pterostigma short, about 0.2 as long as cell r1, filling entire apex of cell R1; thorax blackish except scutellum dark yellow; R4+5 and M1 not distinctly convergent apically..................................................... S. apicalis sp. nov.

2 Antenna dark yellow with first flagellomere dark brown or blackish; wing slightly tinged grayish or grayish brown........ 3

- Antenna brownish with first flagellomere dark brown; wing darker, grayish brown........ S. daqingshanensis Yang et Yang

3 Hind leg brown except coxa and tarsus yellow with tarsomere 5 brown.............. S. xishuangbannaensis Yang et Yang

- Hind leg yellow except basal 0.5 of femur dark brown, apical 0.33 of tibia brown and tarsomere 5 dark brown................................................................................................... S. basalis sp. nov.