Key to Oriental Probolomyrmex ^HNS species based on the worker

1. Petiole posterodorsally with a pair of strong angles/teeth (in dorsal or lateral view)............ 2

- Petiole posterodorsally without a pair of strong angles/teeth; posterodorsal margin at most weakly emarginated medially............................................................................... 3

2. Petiole (including subpetiolar process) as long as high; subpetiolar process developed, subrectangular........................................................................................... bidens Brown ^HNS

- Petiole (including subpetiolar process) distinctly longer than high; subpetiolar process low, with a small anteroventral projection............................................... procne Brown ^HNS

3. Posterodorsal margin of petiole in dorsal view well produced medially into a horn (Fig. 8D)............................................................................................. watanabei Tanaka ^HNS

- Posterodorsal margin of petiole in dorsal view not produced (Figs. 1D, 6D, 7D), or produced but truncate or shallowly emarginate medially (Figs. 2D, 3D, 4D, 5D) ....... 4

4. Posteroventral portion of subpetiolar process spinose, protruding or sharply angled (Figs. 5C, 7C)................................................................................................................ 5

- Posteroventral portion of subpetiolar process rounded or obtusely angled (Figs. 1C, 2C, 3C, 4C, 6C)............................................................................................................. 6

5. Petiole in profile with its posterior outline straight and vertical (above the articulation with gaster); anteroventral projection of subpetiolar process relatively thin and translucent(Fig. 7C) ............................................................................................. vieti ^HNS sp. nov.

- Petiole in profile with its posterior outline concave (above the articulation with gaster); anteroventral projection of subpetiolar process relatively thick and not translucent(Fig. 5C).................................................................................... maryatiae ^HNS sp. nov.

6. Anteroventral portion of subpetiolar process in profile broadly expanded anteroventrad(Fig. 6C)................................................................ okinawensis Terayama et Ogata ^HNS

- Anteroventral portion of subpetiolar process in profile narrowly expanded anteriad or anteroventrad (Figs. 1C, 2C, 3C, 4C)............................................................................ 7

7. Petiolar node in profile with an extremely long and flattened dorsal outline (Fig. 2C); SI>160.......................................................................................................... itoi ^HNS sp. nov.

- Petiolar node in profile with a dorsal outline which is moderately long (or short) and flattened or curved (Figs. 1C, 3C, 4C); SI<150............................................................8

8. Posterior face of propodeum margined laterally with a carina which is angulate dor- sally but only rarely forms a conspicuous propodeal spine (1C); LPtI<135................... ..................................................................................................... dammermani Wheeler ^HNS

- Posterior face of propodeum margined laterally with a carina which forms a triangular propodeal spine (Figs. 3C, 4C); LPtI>135....................................................................9

9. Frontal carina in profile lower, with a semicircular outline (Fig. 9C); 4th antennal segment a little shorter than broad (Fig. 10C)..................... longinodus Terayama et Ogata ^HNS

- Frontal carina in profile higher, with a gently triangular outline (Fig. 9D); 4th antennal segment a little longer than broad (Fig. 10D)........................... longiscapus Xu et Zeng ^HNS