Protandrena Cockerell subgenus Pterosarus Timberlake is the last major group within the North American Andrenidae to have not received a major revision in the United States and Canada, which leaves a large gap in the knowledge of bee biodiversity in the region. The taxonomy of Pr. (Pterosarus) remains unknown in many areas, particularly in Canada and the American West. In order to rectify this, a revision of Pr. (Pterosarus) was completed. Species delimitation followed the process of integration by congruence, with morphological, geographical, and ecological used to delimit species. Morphometric data were analyzed using linear discriminant analysis and partitioning around medioids. Forty-six species were revised, sixteen of which are described as new, thirteen names are treated as junior synonyms, and one name has been elevated from subspecific to specific status. Eight new lectotypes are designated, and the previously unknown females of two species are described. Descriptions, floral record tables, distribution maps, images, and keys to the males and females are provided.