We analyzed 117 specimens from eight Mexican states and 22 localities whose taxonomic identification was doubtful to assign them to Belonuchus ephippiatus or B. erytrhopterus. The goal of this paper is to analyze the most important characters reported in the literature to separate both species and decide if it is one or two entities. The analysis included the measurement of different parts of the body and the proportions between them, but this one focused on the total body length, the number of punctures that form each of the two central rows of the pronotum, the aedeagus length and its proportion in relation to the body length, since they are the most important characters indicated in the literature that allows to separate the two species. The results show that it is not possible to distinguish two species with any of the characters analyzed, combined or alone, so it was proposed for the second time in the history of these species that B. erythropterus is a junior synonym of B. ephippiatus. Aspects of the great morphological variation observed in B. ephippiatus, its geographic distribution and its biology are discussed. Finally, a new species of the same species group is described and it is distinguished from B. ephippiatus, besides providing schemes and photographs that help its recognition.
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