The Onthophagus anthracinus Harold, 1873 (Coleoptera: Scarabaeidae: Scarabaeinae: Onthophagini) species complex of the Onthophagus landolti Harold, 1880 species group is established and analysed. A new species, O. etlaensis, is described from this group. Onthophagus mextexus Howden and Cartwright, 1970 is considered a valid species and O. knulli Howden and Cartwright, 1963 is placed in synonymy with O. durangoensis Balthasar, 1939 new synonymy. A key for the O. anthracinus species complex is presented along with photographs and illustrations of the main taxonomic differences. An update of the O. landolti species group is presented.