A new bee genus from Argentina, Psaenythisca, is described and includes three species: P. flavifrons (Vachal, 1909), n. comb, (originally described as Psaenythia), P. wagneri (Vachal, 1909), n. comb. (originally described as Psaenythia), and P. punctata (Urban, 2009), n. comb. (originally described as Anthrenoides). The new genus is proposed based on a comparative study of the Protandrenini lineages. Psaenythisca is closely related to Cephalurgus and Rhophitulus, and can be distinguished mainly by the forewing with three submarginal cells, premarginal area of S2 to S5 of male with dense pubescence, distal margin of S6 of male slightly emarginated, and male genitalia with relatively broad basal sclerite. Among Protandrenini genera with three submarginal cells, it differs from Anthrenoides and Psaenythia by the combination of male genitalia with a basal sclerite, metasomal terga lacking yellow markings, propodeum rounded, middle tibial spur of the female finely serrate, and slender basal area of S8 of male. In addition, a lectotype is designated for Psaenythia (Psaenythia) wagneri Vachal, 1909. The holotype of P. flavifrons and the lectotype of P. wagneri are redescribed, and the female of P. flavifrons and male of P. punctata are described for the first time. An identification key to, and distribution maps of, the species of Psaenythisca are also provided.

Nearly a quarter of a century ago, Arturo Roig-Alsina and the second author discovered a communal nest of one of the species, now known as Psaenythisca wagneri (Vachal, 1909). The nest descended approximately 2 m into the ground and is described herein. From this nest, provision masses, eggs, larvae, and pupae were retrieved as well as developmental and behavioral information. The immatures are described and compared with those of related taxa, and the developmental and behavioral information are recorded. Of special interest is the fact that males exhibit a wide range of head sizes and head shapes. All of this gives rise to intriguing new questions for future investigation.