Genus Syscia Roger, 1861

Key to Asian species of Syscia Roger, 1861 based on the worker caste

1. Antennae with 9 segments (Figs 9A, 10D) ....................................................................................... 2

– Antennae with 11 segments (Figs 2C, 3A, 4D, 5A, 7A) .................................................................. 3

2. Mesosoma rather elongate, long-ellipsoidal, with lateral sides and anterior margin obviously convex in dorsal view (Fig. 9C); both anterior margin and posterior margin of petiole convex in lateral view (Fig. 9D); posteroventral corner of subpetiolar process blunt rounded in lateral view (Fig. 9D); postpetiole in dorsal view longer than wide (Fig. 9C) ..................................... S. typhla Roger, 1861

– Mesosoma rather robust, subrectangular with almost parallel lateral sides, and anterior margin slightly convex in dorsal view (Fig. 10C); both anterior margin and posterior margin of petiole straight in lateral view (Fig. 10D); posteroventral corner of subpetiolar process acute angled in lateral view (Fig. 10D); postpetiole in dorsal view wider than long (Fig. 10B) ....... S. zhoui sp. nov.

3. Head in full-face view oval (Figs 2A, 8B) ....................................................................................... 4

– Head in full-face view rectangular or trapezoidal (Figs 3B, 4A, 5A, 6A, 7A, 8B) .......................... 5

4. Body entire reticulate, with deep bottoms (Fig. 8) ............................................................................. ....................................................... S. reticularis reticularis Jaitrong Wiwatwitaya & Yamane, 2020

– Body covered with punctures or shallow fovea (Fig. 2) ................................... S. arcodorsa sp. nov.

5. Petiole in dorsal view broader than long (Fig. 3C); in lateral view the front and the back margins of the petiole vertical (Fig. 3A) .............. S. chaladthanyakiji Jaitrong, Wiwatwitaya & Yamane, 2020

– Petiole in dorsal view longer than broad or as long as broad (Figs 4C, 5B, 6B, 7B); in lateral view the front and the back margins of petiole steep or sloped (Figs 4D, 5D, 6C, 7C) ............................ 7

6. Subpetiolar process in lateral view subtriangular (Fig. 4C); anterior margin of petiole slightly convex (Fig. 4D) ................................................................................................. S. humicola (Ogata, 1983)

– Subpetiolar process in lateral view subrectangular (Figs 5D, 6C, 6B, 7C); anterior margin of petiole slightly concave ................................................................................................................................ 7

7. Propodeal declivity straight or slightly convex in lateral view (Figs 6–7) ......................................... ................................................................................................................. S. guizhouensis comb. nov.

– Propodeal declivity slightly concave in lateral view (Fig. 5) ............................................................. .............................. S. indica Aswaj, Sahanashree, Udayakantha, Aniruddha & Priyadarsanan, 2021