Key to Nigidius species in the obesus group

1. Pronotal disc each side of me dian sulcus with small but deep punctures, thus surface appearing entirely punctate (Fig. 8); Sumatra .............................. N. helleri Boileau

– Pronotal disc each side of median sulcus with minute, shallow punctures, thus appearing nearly impunctate, contrasting with adjacent groups of coarse punctures (Fig. 9); not from Sumatra ................................................................... 2

2. Elytral intervals almost impunctate medially, appearing more carinate (intervals with punctures only lateral, adjacent to striae); peninsular Malaysia ................. N. obesus Parry

– Elytral intervals punctate medially thus appearing less strongly carinate (intervals irregularly punctate); not from peninsular Malaysia ......................................... 3

3. Male genitalia with flagellum sinuous, with small lobe near apex (Fig. 11); Southeast Asia...................................................... N. dawnae Gravely

– Male genitalia with flagellum overall straight, with large lateral lobe distant from apex (Fig. 12); Borneo.............................................. N. gravelyi Paulsen, n. sp.