Key to adult males of Heterotrissocladius in China

1. AR> 1.0, squama with 25–48 setae, thorax with 8–14 prealars.................................................. 2

-. AR <1.0, squama with 6–12 setae, thorax with 4–5 prealars.................................................... 3

2. Whole wing membrane covered with setae, cell an with more than 450 setae, AR1.2–1.3 (except one specimen from Gansu province 0.83)....................................................................... H. marcidus (Walker)

-. Wing membrane covered with setae on apical half, cell an with 0–162 setae, AR nearly 1.5..... H. scutellatus (Goetghebuer)

3. Palp with 4 palpomeres, Cu1 less than 200 Μm long.............................................. H. quartus sp. n.

-. Palp with 5 palpomeres, Cu1 usually more than 300 Μm long................................................... 4

4. Anal lobe of wing well developed, apex of inferior volsella narrowed and distinctly bent, gonostylus with triangular crista dor- salis.................................................................................... H. flectus sp. n.

-. Anal lobe of wing reduced, apex of inferior volsella broad and straight, gonostylus with pointed crista dorsalis................................................................................................... H. reductus sp. n.