Key to Mexican species of Exenterus

1. Female. Antenna yellow or brownish yellow, at most scape, pedicel and a few basal flagellomeres infuscate dorsally (Figs 8, 9). Propleuron, metapleuron and propodeum yellow or yellow-marked (Fig. 10). Hind coxa yellow at least in its ventral half (Fig. 10). Metasomal tergite 2 black with conspicuous posterior yellow band (Fig. 20)................................ 2

- Male. Antenna dorsally, propleuron, metapleuron, propodeum, hind coxa and metasomal tergite 2 black (Figs 22, 24)..... 3

2. Hind tarsus, in dorsal view, with tarsomere 3 distinctly elongate (Fig. 1). Tergite 3 with transverse yellow band in posterior 0.5 (Fig. 3). Pronotum entirely yellow...................................................... E. durangensis sp. nov.

- Hind tarsus, in dorsal view, with tarsomere 3 transverse or as long as broad (Figs 2, 17). Tergite 3 with transverse yellow band in posterior 0.2–0.25 (Fig. 4). Pronotum yellow with conspicuous dorsomedian and lateral black markings (Figs 12, 14).................................................................................... E. sehuerachicus sp. nov.

3. Epomia almost straight, converging towards anterior margin of pronotum ventrally and more or less reaching it (Fig. 6). Genae black with eye orbits narrowly yellow-banded (Fig. 5). Mandible black basally (Fig. 5). Mesosoma black with only subtegular prominence and extreme hind margins of scutelum and postscutellum yellow................... E. durangensis sp. nov.

- Epomia with lower half subparallel to anterior margin of pronotum, ending far from it, and with upper end weakly but distinctly curved (Fig. 7). Genae with yellow eye orbits distinctly widened ventrally, thus the entire lower 0.2–0.3 of gena is yellow (Fig. 22). Mandible yellow basally (Fig. 21). Mesosoma black with yellow stripes on anterior margin and lateral side of pronotum, lateral stripes on mesoscutum, posterior about 0.7 of scutellum, entire postscutellum, subtegular prominence and conspicuous mark on mesopleuron above the upper end of epicnemial carina (Fig. 22).......... E. sehuerachicus sp. nov.