Key to the species in the Onthophagus anthracinus species complex

1. Pygidium apically convex, shiny, and smooth; distinctly punctate; alutaceus basally (Fig. 7). Pronotal punctures with indistinct margin, (Fig. 8) ........................................................................ 2

– Pygidium almost flat, shallowly and indistinctly punctate, alutaceous basally; apex less shiny and alutaceous (Fig. 9). Pronotal punctures with distinct margins, often appearing like a shiny, ocellate ring, (Fig. 10) ...................................................................................................... 3

2. Posterior half of metaventrite medially impunctate or with one or two course punctures (Fig. 11). Usually occurs in lowland alluvial habitats from Texas, United States of America to Oaxaca, Mexico ................................ Onthophagus alluvius Howden and Cartwright, 1963

– Posterior half of metaventrite medially with a few coarse punctures near midline, as coarsely punctate medially as laterally with larger punctures (Fig. 12). Usually occurs in montaine habitats from Arizona, United States of America to Sierra Madre Occidental and the Transverse Volcanic System (Federal District, Mexico) ............................................................ ........................................................................................ Onthophagus durangoensis Balthasar, 1939

3. Pronotal punctures umbilicate (Fig. 10); small, shallow, nonsetate secondary punctures abundantly scattered among large punctures. Big Bend region of Texas, United States of America to Veracruz, Mexico .................................................................................................................. .................................................................. Onthophagus mextexus Howden and Cartwright, 1970

– Pronotal punctures not umbilicate, like a shiny ring (Fig. 13); small, shallow nonsetate secondary punctures sparsely scattered among large punctures. Oaxaca Highlands, Mexico to Chiriquí, Panama ................................................................................................................................ 4

4. Pronotal punctures 75 μm in diameter with an evident shiny ring, punctures separated by approximately one puncture diameter (Fig. 13). Pronotal longitudinal sulcus evident in major males (Fig. 13), area around it convex. Phallobase with a distinct ring (Fig. 19), internal sac lamella as in Figure 22. Oaxaca, Mexico ...................................................................... ........................................................................................................ Onthophagus etlaensis new species

– Pronotal punctures 50 μm in diameter with no evident shiny ring, separated by 1–2 puncture diameters (Fig. 14). Pronotal midline well marked in major males (Fig. 14), pronotal area around it flattened forming a rhombus. Phallobase with an indistinct ring (Fig. 17), internal sac lamella as in Fig. 21. Chiapas, Mexico to Chiriquí, Panama .................. .............................................................................................. Onthophagus anthracinus Harold, 1873