Key to the species of genus Ommatidiotus Spinola in Northeast Asia (modified from Horváth, 1905 and Anufriev & Emeljanov, 1988)

MALE

1. Coryphe elongated, length more than 1.5 times longer than width............................................... 2

- Coryphe not elongated, length almost as long as width....................................................... 6

2. Coryphe almost 1.5 times longer than width................................................................ 3

- Coryphe more 2 times longer than width.................................................................. 4

3. Coryphe less 1.5 times longer than width, anterior margins relatively pointed at apex...... O. japonicus Hori (Japan, China)

- Coryphe more 2 times longer than width, anterior margins rounded at apex......... O. longiceps Puton (Mongolia (North))

4. Metope with median carinae whitish, contrasted with background.............................................. 5

- Metope with median carinae blackish, concolorous with background.. O. koreanus Matsumura (North Korea, Russia, Japan)

5. Forewing with veins brown, contrast with background.................... O. acutus Horváth (China, Mongolia, Russia)

- Forewing with veins concolorous with background.................... O. pseudolongiceps Meng, Qin & Wang (China)

6. Forewing with blackish markings on costal area, distinctly contrast with background............................... 7

- Forewing without blackish markings on costal area, concolorous with background.......... O. inconspicuus Stål (Russia)

7. Body size more than 3.0 mm (including forewing)........................................................... 8

- Body size less than 3.0 mm (including forewing)............................ O. dashdorzhi Dlabola (China, Mongolia)

8. Aedeagus in posterodorsal view, lateral processes relatively long, protruding downward............................. 9

- Aedeagus in posterodorsal view, lateral processes relatively short, protruding upward....... O. nigritus Matsumura (Russia)

9. Aedeagus in posterodorsal view lateral processes reaching at base, not connected............................................................................................. O. dissimilis (Fallén) (North Korea *, Transpalearctic)

- Aedeagus in posterodorsal view lateral processes not reaching at base, connected by short transverse cross-piece shaped............................................................................. O. sylvaticus Emeljanov (Russia)

FEMALE

1. Coryphe elongated, length more than 1.5 times longer than width............................................... 2

- Coryphe not elongated, length almost as long as width....................................................... 6

2. Coryphe almost 1.5 times longer than width................................................................ 3

- Coryphe more 2 times longer than width.................................................................. 4

3. Coryphe less 1.5 times longer than width, anterior margins relatively pointed at apex........... O. japonicus Hori (Japan)

- Coryphe more 2 times longer than width, anterior margins rounded at apex......... O. longiceps Puton (Mongolia (North))

4. Metope with median carinae whitish, contrasted with background.............................................. 5

- Metope with median carinae blackish, concolorous with background.............. O. koreanus Matsumura (North Korea)

5. Forewing with veins brown, contrast with background.................... O. acutus Horváth (China, Mongolia, Russia)

- Forewing with veins concolorous with background.................... O. pseudolongiceps Meng, Qin & Wang (China)

6. General coloration of body light brown to brown, dorsal and ventral colorations contrasted.......................... 7

- General coloration of body black, dorsal and ventral colorations not contrasted............ O. nigritus Matsumura (Russia)

7. Coryphe with longitudinal dark stripes with a narrow reddish stripe medially, contrasted bicolored..................... 8

- Coryphe with longitudinal stripes broad brown or reddish medially, unicolored.................................... 9

8. Anterior margins of coryphe round............................... O. dissimilis (Fallén) (North Korea *, Russia, Japan)

- Anterior margins of coryphe slightly angulated..................................... O. inconspicuous Stål (Russia)

9. Body size less than 4.5 mm (including forewing)........................................................... 10

- Body size more than 4.5 mm (including forewing)............. O. karafutonis Matsumura stat. rev. (North Korea, Russia)

10. Cubital and median cells of forewing without stripes................................. O. dashdorzhi Dlabola (China)

- Cubital and median cells of forewing with longitudinal reddish-brown stripes........... O. sylvaticus Emeljanov (Russia)