A new species, Pseudacanthus alani n. sp., is described from cloud forest in Oaxaca, Mexico. This species is similar to Pseudacanthus junctistriatus Kuwert 1891 in size, shape of antennal lamella, and the absence of pubescence on abdominal terga, but has larger internal tubercles, an apex of central tubercle that is not free, glabrous elytral humerus, pubescent mesepisternum and mesepimeron and mesosternal scar, and male sexual characters. Photographs are provided of the head, male and female genitalia, and plectrum. Additionally, a taxonomic key to species of Pseudacanthus Kaup 1869 is provided, complemented with photographs of diagnostic characters. Finally, we propose two junior synonyms: Pseudacanthus solidus (Arrow 1907) n. syn. of Pseudacanthus junctistriatus and Pseudacanthus truquii Kuwert 1891 n. syn. of Pseudacanthus mexicanus (Truqui 1857).
Keywords: Bess beetles; Proculini; cloud forest; plectrum; taxonomy.