Technical Abstract: As part of ongoing investigations on anthidiine bees, the type of Anthidium albitarse Friese was found to be conspecific with one of the two species of the small resin bees Hypanthidioides subgenus Michanthidium. The new combination, H. (Michanthidium) albitarse, is the oldest name resulting in Gnathanthidium sakagamii Urban as a new junior synonym. The previously unknown male of the second species, H. ferrugineum, is also described and figured, including the genitalic structure and associated sterna. Males and females of H. ferrugineum have been collected from flowers of Cuphea sp. (Lythraceae).