Key to the Taiwanese species of Leptophion

1. Hind wing with non-uniform shaped hamuli on R1, penultimate hamulus significantly elongated (Fig. 13). Proximal part of marginal cell of fore wing with an infumate area (Fig. 32). Postero-proximal part of second subdiscal cell of fore wing entirely hyaline without an infumate area (Fig. 32). Proximal corner of marginal cell of hind wing about 95° (Fig. 32). Lateral carinae of scutellum developed on anterior 0.8–0.9 (Fig. 11)................................ L. maculipennis (Cameron, 1905)

- Hind wing with uniform hamuli on R1, penultimate hamulus not elongated (Figs 21, 30). Proximal part of marginal cell of fore wing with an infumate area (Figs 33, 34). Postero-proximal part of second subdiscal cell of fore wing with an infumate area (Figs 33, 34). Proximal corner of marginal cell of hind wing about 45° (Figs 33, 34). Lateral carinae of scutellum developed on anterior 0.2 (Figs 19, 28)................................................................................ 2

2. 1m-cu of fore wing strongly sinuous (Fig. 33). Postero-distal corner of second discal cell of fore wing forming an obtuse angle, about 105–110° (Fig. 33). Fore wing with AI=1.1–1.4; ICI=0.9–1.0; SDI=1.1–1.2 (Fig. 33). Fore wing weakly infumate except for proximal part of marginal cell often with a more or less distinct infumate area (but occasionally no more infumate than apex of cell), and postero-proximal part of second subdiscal cell with a distinct infumate area (Fig. 33). Fore wing 17.0–21.0 mm............................................................... L. giganteus Shimizu & Watanabe, sp. nov.

- 1m-cu of fore wing abruptly curved (Fig. 34). Postero-distal corner of second discal cell of fore wing forming an acute angle, about 85° (Fig. 34). Fore wing with AI=0.8–0.9; ICI=0.5–0.7; SDI=0.9–1.0 (Fig. 34). Fore wing hyaline except for proximal part of marginal cell and postero-proximal corner of second subdiscal cell each with an infumate area (Fig. 34). Fore wing 13.0–15.0 mm.................................................................... L. radiatus (Uchida, 1956)