Key to the O. belorhinus species complex, based on major males

(modified from Moctezuma et al. 2020). Note that O. genuinus Kolmann & Solís, 2001 is excluded from this species complex based on the redefinition by Montezuma et al. (2020).

1 Anterior midline of pronotum moderately to strongly impressed................................................ 2

- Anterior midline of pronotum obsolete, Oaxaca (Santa María Chimalapa; Fig. 2)....................................................................................... O. istmenus Moctezuma, Sánchez-Huerta, & Halffter, 2020

2 Bifurcation of clypeal horn V-shaped, Costa Rica (Fig. 2)................... O. grataehelenae Kohlmann & Solís, 2001

- Bifurcation of clypeal horn broadly U-shaped.............................................................. 3

3 Bifurcation of strongly elongate clypeal horn reaching to the gena, with an indentation at the apex; Costa Rica (Fig. 2)............................................................................ O. andersoni Howden & Gill, 1987

- Bifurcation of clypeal horn elongate, projecting over the clypeus but not reaching the gena, sinuate or straight without indentation apically......................................................................................... 4

4 Anterior half of pronotum with two lateral concavities and a weak medial-frontal tubercle, Chiapas (Tacaná Volcano; Fig. 2).............................................. O. tacanensis Chamé-Vázquez & Sánchez-Hernández, new species

- Anterior half of pronotum without concavities and frontal median tubercle formed by two distinct protuberances, central Mexico to El Salvador (Fig. 2).......................................................... O. belorhinus Bates, 1887