Ophiogomphus Lieftinck 1964

Key to the males and females of Ophiogomphus species of Vietnam

Males

1 Anterior hamulus with anterior branch long and slender occupying about 2/3 of anterior hamuli length (Fig. 20); basal hamulus tooth with a weakly developed................................................................ longihamulus

- Anterior hamulus with anterior branch comparatively short and broad, occupying about a half of anterior hamulus length (Figs 22, 24, 26); basal hamulus tooth broader and forming a triangular lobe........................................... 2

2 Posterior hamulus in lateral view curvilinear, narrowed apically ending in a narrow spatulate lobe; cornua of glans short, branches widely separated apically (Fig. 27); larger species (Abdomen: 46 mm; Hw 37 mm)..................... sinicus

- Posterior hamulus in lateral view hook-shaped, stockier apically ending in a thicker spatulate lobe (Figs 22, 24); cornua of glans long, widely, deeply incised, U- or V-shaped (Figs 23, 25); smaller species (Abdomen: 37–39 mm; Hw 29–31.5 mm)...... 3

3 Lobe of penis vesicle strongly protruded ventrally. Cornua of glans short, U-shaped (Fig. 23)................... minimus

- Lobe of penis vesicle short in ventrally. Cornua of glans long, V-shaped (Fig. 25)........................... phantoani

Females

1 Vulvar lamina triangularly excavated at apex (Figs 29, 35)..................................................... 2

- Vulvar lamina with lobes approximate or narrowly U-shaped (Figs 31, 33)........................................ 3

2 Vulvar lamina nearly as long as S9, lobes widely separated apically (Fig. 29)............................ longihamulus

- Vulvar lamina half as long as S9 (Fig. 35).............................................................. sinicus

3 Vulvar lamina pointed in apex; occiput with two widely separated, serrated, sharp marginal projections (Figs 32, 33)................................................................................................... phantoani

- Vulvar lamina incised apically; occiput with two erect, rounded marginal projections (Figs 30, 31)............... minimus