Key to the males of Sinotilla with a weak ventral lobe on the mandible

1. Clypeus with a pair of subapical rounded tubercles; T2 abruptly convex.......................................... 2

- Clypeus without subapical tubercles; T2 evenly convex....................................................... 4

2. Tegula projecting posteriorly, reaching half of scutellum; metasoma without bluish metallic luster; apical pale fringes on T1–T3 dense............................................................................................... 3

- Tegula weakly projecting postero-laterally, slightly protruding beyond mesoscuto-scutellar articulation; metasoma with distinct bluish metallic luster; apical pale fringes on T1–T3 sparse; species from Okinawa-jima Is., Japan ........ Si. jambar sp. nov.

3. Mesosoma black except pronotum and mesoscutum yellowish red; species from Taiwan ......... Si. serpa serpa (Zavattari)

- Mesosoma yellowish red, including scutellum and metanotum, propodeum and mesopleuron black; species from China mainland........................................................................... Si. serpa columnata (Chen)

4. Mesosoma more or less yellowish red; metasoma black; POL/OOL 0.5–0.8....................................... 5

- Mesosoma black; metasoma with T1–T2 and S1–S2 yellowish red; POL/OOL = 0.68–0.75.............. Si. trisecta (Chen)

5. POL/OOL = 0.8; species from China mainland.................................................... Si. hong Lelej

- POL/OOL = 0.50–0.65; species from Malaysia and Indonesia ................................. Si. runcina (Zavattari)