This, the only genus of the subfamily Pioninae, now includes 33 species from the United States. Detailed descriptions, with figures, are given for 30 of these, including 11 that are new: P. michiganensis, P. conglobatella, P. pinguipalpis, P. mitchelli, and P. haberba (Michigan, P. brunsoni (Montana and Michigan), P. flatheadensis (Montana), P. loda (Montana and Washington), P. washingtonensis (Washington), P. spangleri (Missouri), and P. floridana (Florida). ... Present genera of Piona, based on female characters, are quite unsatisfactory. Characters of the males offer better criteria for grouping the species, but any new subgeneric revision should be based on the world fauna and not on that of the United States alone.