Key to males of species of the baconii species group

1 Eyes very large and prominent, head wider than long, aedeagus broadly expanded medially ( baconii species group)....... 2

- Eyes large or quite small, head longer than wide, aedeagus not expanded medially............. other Orthogonius species

2 First hind tarsomere shorter than 5th, median lobe of aedeagus slightly expanded ventrally at middle portion, apex distinctly sharp in lateral view, apical lamella pointed at apex........................................... O. nepalensis Habu

- First hind tarsomere longer than 5th, median lobe of aedeagus distinctly expanded ventrally at middle portion, apex more or less

blunt in lateral view, apical lamella obtuse at apex........................................................... 3 3 Median lobe of aedeagus stouter, strongly expanded ventrally at middle portion (Figs 11–12)............ O. rogueti n. sp.

- Median lobe of aedeagus more slender, moderately expanded ventrally at middle portion, apical lamella stout, at least as wide as long............................................................................................ 4

4 Apical lamella of median lobe of aedeagus elongated, longer than wide, broader at apex (Figs 4–5).... O. baconii Chaudoir

- Apical lamella of median lobe of aedeagus stout, as long as wide, narrower at apex (Figs 7–8)......... O. ceylanicus n. sp.