Megarthrus

Key to the species of Megarthrus from southern India and Sri Lanka

1 Body predominantly rust brown or chestnut brown; elytra unicolored; antennomeres 9 and 10 strongly asymmetrical (fig. 63); frons with lateral outlines oblique to apex broadly rounded, or subtruncate. Male: protarsomeres 5 with conspicuous adventral apophysis; mesotibiae markedly arcuate (fig. 56) (rufomarginatus -complex)....................................... 2

- Body predominantly yellow brown; elytra bicoloured; antennomeres 9 and 10 symmetrical; frons with lateral outlines markedly concave to apex truncate. Male: protarsomeres 5 without adventral apophysis; mesotibiae fairly straight (fig. 20) (bimaculatus -complex)................................................................................. 3

2 Body chestnut brown, except legs and antennae paler; antennae unicoloured. Male: aedeagus (figs 66–68) with sclerotized dorsal valve longer than half the distance from its posterior edge to the aedeagal tip; internal sac with a very large subbasal sclerite; abdominal sternite V with medial area slightly swollen and bearing a short transverse ridge. Female: valvifers in dorsal view gradually tapering, with lateral outline gently convex (fig. 71); dorsal outline of valvifers almost straight (fig. 72); genital tergites with a medial macula cordiform (fig. 70)........................... Megarthrus rufomarginatus (fig. 2)

- Body rust brown, concolorous with legs and antennae, except antennomeres 11 markedly paler than the others. Male: aedeagus (figs 48–51) with sclerotized dorsal valve not longer than half the distance from its posterior edge to the aedeagal tip; internal sac with a subbasal group of strong spines; abdominal sternite V with medial area slightly swollen and bearing a short transverse ridge. Female: valvifers in dorsal view evenly tapering, with lateral outline almost straight (fig. 58); dorsal outline of valvifers angulate subapically (fig. 59); genital tergites with a medial macula oval (fig. 60)..... Megarthrus lanka (fig. 1)

3 Male: aedeagus with ventral wall subapically right angled, apical portion conspicuously projecting ventrally (figs 32, 33). Female: valvifers each with a dorsal apophysis locate at level of dorsobasal margin (fig. 41) … Megarthrus nilgiriensis (fig. 5)

- Male: aedeagus with ventral wall subapically not right angled. Female: valvifers each with a dorsal apophysis located near midlength (figs 12, 24)................................................................................ 4

4 Male: aedeagus with ventral outline of ventral wall sinuate to tip truncate (figs 16, 17). Female: lateral outline of middle portion of valvifers converging (fig. 23); female: genital tergites with two transverse subbasal sclerites (fig. 25)......................................................................................... Megarthrus narendrani (fig. 4)

- Male: aedeagus with ventral outline of ventral wall arcuate to tip blunt (figs 7, 8). Female: lateral outline of middle portion of valvifers parallel (fig. 11); female: genital tergites without subbasal sclerites (fig. 3)....... Megarthrus bimaculatus (fig. 3)