The Acanthoscelides oblongoguttatus group of Acanthoscelides Schilsky is composed of two species that are often collected together associated with ant-acacias in the genus Vachellia Wight & Arn. (Fabaceae). Acanthoscelides oblongoguttatus (Fåhraeus) was described first and was redescribed in a modern revision of the genus. However, the redescription was based on a second, undescribed species and did not conform to the original description. When a second species, Acanthoscelides sauli Romero, Cruz, and Kingsolver, was described, it was instead a redescription of A. oblongoguttatus. To rectify this situation, A. sauli is here proposed as a junior synonym of A. oblongoguttatus, new synonymy, a lectotype is designated for A. oblongoguttatus, and Acanthoscelides sanchezsotoi Morse, new species is described.