Key to the species of the plagiatus group

1 Distance between ocelli distinctly longer than distance between ocellus and posterior margin of eye................... 2

- Distance between ocelli as long as distance between ocellus and posterior margin of eye or slightly shorter.............. 7

2 Aedeagus with very narrow median lobe and significantly broadened apical portions of parameres (Cheng et al. 2021: fig. 68). Body length: 4.0– 5.8 mm. Habitus as in Cheng et al. (2020: fig. 58). Russia, China ..................... G. paramerus

- Aedeagus with broader median lobe and significantly narrower apical portions of parameres......................... 3

3 Pronotum distinctly transverse, strongly narrowed posteriad. Median lobe moderately wide (Fig. 29). Body brown. Body length: 6.2–6.7 mm. Habitus as in Figs. 8. Corsica ........................................................ G. corsicus

- Pronotum slightly transverse, gradually narrowed posteriad. Median lobe narrow. Body brown to black, sometimes with a pale spot on each elytron................................................................................... 4

4 Elytra wide, usually 1.8 times as broad as pronotum, with elongate reddish-yellow spot along suture. Parameres extending distinctly beyond apex of median lobe (Figs. 33–34). Body length: 4.8–6.2 mm. Habitus as in Fig. 9. Middle Europe................................................................................................. G. suturalis

- Elytra narrower, about 1.6 times as broad as pronotum, unicolored or with reddish spot in middle portion of each elytron. Parameres not extending, or only slightly, beyond apex of median lobe.......................................... 5

5 Median lobe with concave latero-apical margins (Figs. 31–32). Body length: 5.6–6.3 mm. Habitus as in Fig. 10. Middle Europe................................................................................ G. pedemontanus

- Median lobe with latero-apical margins gradually narrowed toward apex......................................... 6

6 Each elytron without or sometimes with yellow-brown to brownish-red oblique spot. Apical portion of median lobe narrow, gradually narrowed toward subacute apex (Figs. 12–26). Legs yellow-brown to brown. Body length: 3.9–6.7 mm. Habitus as in Figs. 1, 3, 5–7. Palaearctic Region............................................................ G. plagiatus

- Elytra without spots. Apical portion of median lobe moderately wide, sharply narrowed toward rounded apex (Figs. 36–39). Legs brown to black. Body length: 4.2–6.5 mm. Habitus as in Fig. 9. Europe............................... G. nigrita

7 Elytra as broad as long. Median lobe gradually narrowed toward widely rounded apex (Cheng et al. 2020: fig. 55). Body brown to black. Body length: 5.5–7.4 mm. Habitus as in Cheng et al. (2020: fig. 54). China ....................... G. magnus

- Elytra slightly longer than long. Median lobe sharply narrowed before middle toward lancet-shaped apex (Cheng et al. 2020: figs. 85, 87–89: figs. 85, 87–89)). Body brown to reddish-brown. Body length: 4.3–5.6 mm. Habitus as in Cheng et al. (2020: fig. 81). China .................................................................................. G. shii