Key to the genera Ctenocerus Dahlbom, 1845 and Paraclavelia Haupt, 1930

(The key is not specific to the Asian species but applies to the African species.)

Females

1. Lower frons lateral to and ventral to antennal sockets deeply depressed, leaving frontal bridge (Figs 1A, F, J, 2E, G, I, 3D, arrow) this being continuous to clypeus on same plane; clypeus deeply and broadly depressed only basilaterally; fore femur swollen, thicker than mid femur (Figs 2A, F, H, J, 3H) ....................................................................................................... Ctenocerus Dahlbom, 1845

– Frontal bridge absent, i.e., lower frons deeply depressed lateral to antennal sockets and ventral to them across its whole width (Figs 6A, D, G, J, 7D); clypeus with deep depression across whole width of its base, depression being broader laterally than medially; fore femur not swollen (Figs 6F, I, 7H) .......................................................................................................... Paraclavelia Haupt, 1930

Males

1. Supra-antennal area of frons not or slightly produced anteriorly (Figs 4C, F, I, 5G); lower frons with frontal bridge (Figs 4A, D, G, 5D, arrow), this being sometimes narrow and slightly depressed below level of supra-antennal area unlike in female .............................. Ctenocerus Dahlbom, 1845

– Supra-antennal area of frons produced into frontal ledge overhanging antennal radicle (Fig. 8C, F, I); frontal bridge absent (Fig. 8A, D, G), i.e., lowermost frons across its whole width depressed much below level of supra-antennal area and slightly below level of clypeus ... Paraclavelia Haupt, 1930

Based on these key characters, at least Ct. decipiens, which is known only from a male from South Africa, should be transferred to Paraclavelia. Examination of the males of this species has revealed that they bear the characteristics of Paraclavelia, i.e., the frons protruded over the antennal sockets (Fig. 8F) and lacking the frontal bridge (Fig. 8D), although the flagellum is biramous (Figs 8D–F, K). Moreover, the male of Ct. srilankae sp. nov. has the crenulate flagellum (Fig. 5H). Thus, the males of both Ctenocerus and Paraclavelia may have the flagellum uni- or biramous, or crenulate, as discussed below, invalidating this character as diagnostic for the genera as proposed by Arnold (1932).