The maxillary palpi of Osmia (sens. lat.) are given by most authors as four-jointed. I have examined the maxillary palpi of sixteen species in this group, and find in every instance that these palpi are five-jointed. The first joint is usually small, sometimes globular in shape, and visible with a hand-lens only under very favorable conditions. The following species were examined: From the coll. of the State Agr'l College of Colorado—O. armaticeps; Cr.; Coloradensis, Cr.; dubia, Cr.; fulgida, Cr.; integra, Cr.; lignaria, Say, and mandibularis, Cr., all from Colorado.