Key to Chinese species of the genus Omalus

1. T3 with wide semitransparent rim (≥ 1 MOD).............................................................. 2

- T3 without semitransparent rim or with narrow semitransparent rim (≤0.5 MOD)................................... 5

2. Mesoscutum weakly wrinkled; notauli distinct and complete.................................. O. corrugatus sp. nov.

- Mesoscutum polished without wrinkles; notauli indistinct or absent............................................. 3

3. Tarsal claw with four teeth............................................................... O. timidus (Nurse)

- Tarsal claw with three teeth............................................................................ 4

4. Mesoscutellum evenly punctate and with two anterior foveae; metanotum gibbous with round and subequally spaced punctures.................................................................................. O. hainanensis sp. nov.

- Mesoscutellum largely polished and without anterior foveae; metanotum prominent with irregular and large punctures without interspaces....................................................................... O. potanini (Semenov)

5. Tarsal claw with four teeth............................................................................ 6

- Tarsal claw with three teeth............................................................................. 8

6. Mesoscutum weakly wrinkled............................................. O. probiaccinctus Wei, Rosa, Liu & Xu

- Mesoscutum polished, at most punctate................................................................... 7

7. Body light metallic green with golden reflections; medial vein short and strongly arched. O. stella (Semenov & Nikol'skaya)

- Female body metallic blue sometimes with violet reflections and male body metallic blue to green, often dorsally blackish; medial vein longer and gently curved.................................................... O. aeneus (Fabricius)

8. Notauli distinct and deep............................................................................... 9

- Notauli indistinct and shallow, impressed as fine lines....................................................... 10

9. Pronotum with scattered and shallow punctures medially; metasoma pear-shaped; T2 distinctly wider than T1; T3 with median notch V-shaped.................................................................. O. berezovskii (Semenov)

- Pronotum almost impunctate medially; metasoma distinctly elongate; T2 not wider than T1; T3 with median notch shallowly indented................................................................. O. tibetanus Wei, Rosa, Liu & Xu

10. Mesoscutellum without anterior foveae...................................... O. helanshanus Wei, Rosa, Liu & Xu

- Mesoscutellum with two anterior foveae................................................................. 11

11. Tegula fully metallic blue; mesopleuron without striae among punctures; propodeal angle indistinct. O. imbecillus (Mocsáry)

- Tegula transparent brown, with faint metallic reflections anteriorly; mesopleuron with striae among punctures; propodeal angle distinct and stout.................................................... .. O. pseudoimbecillus Wei, Rosa, Liu & Xu