Key to the males and females of the hayashii -group in Vietnam

Males: Fully mature males are used in this key because the body color pattern of C. mattii (and probably in most Coeliccia species) shown the development of pruinosity with present the antehumeral markings on immature stage, but largely black in full mature ones (Phan et al. 2020).

1 Synthorax with yellow antehumeral markings.............................................................. 2

- Synthorax lacking antehumeral markings.................................................................. 4

2 Synthorax without pruinosity; antehumeral markings short, oval shaped; S9–10 yellowish (Kompier et al. 2020: Fig. 27a).............................................................................................. diomedea

- Synthorax with pruinosity; antehumeral markings as long as the length of mesepisternum........................... 3

3 Synthorax with a large triangular pruinose marking; antehumeral markings thin; S9–10 including appendages yellow (Phan & Kompier 2016: Figs 3A, 4A)...................................................................... hayashii

- Synthorax with a small pruinose squarish spot; antehumeral markings broad apically then narrowing; S9 black, S10 yellow with a dorsal black marking (Kompier et al. 2020: Fig. 26e)................................................. coronata

4 Synthorax without pruinosity (Figs 17, 18)............................................................. natgeo

- Synthorax with pruinosity.............................................................................. 5

5 Most synthorax is covered by pruinosity (Phan & Kompier 2016: Fig. 3C)................................... mattii

- Synthorax with pruinose spot(s)......................................................................... 6

6 Synthorax largely black with gray-blue pruinose spots and bluish stripes; S8–10 pale blue; anal appendages white (Phan & To 2019: Figs 5, 8)................................................................................. schorri

- Synthorax with large rectangular pruinose areas; S8 black, S9–10 including anal appendages yellowish................ 7

7 The large rectangular pruinose markings confined to the mesepimeron; metepisternum yellowish (Phan 2019: Fig. 9).................................................................................................. lecongcoi

- The large rectangular pruinose markings covering part of both metepisternum and mesepimeron; metepisternum black (Phan 2019: Fig. 10).................................................................................... duytan