The viduatus species-group of Nearctic Pachybrachis Chevrolat, 1836 is defined and revised. The group is composed of nine species, including four described as new species: Pachybrachis bloxham Riley and Barney, Pachybrachis chester Riley and Barney, Pachybrachis deceptor Riley and Barney, and Pachybrachis kentuckyensis Riley and Barney. Lectotypes are designated for Cryptocephalus m-nigrum Melsheimer, 1847, Cryptocephalus trinotatus Melsheimer,1847, and Pachybrachys intricatus Suffrian, 1852, and a neotype is designated for Cryptocephalus viduatus F., 1801. A key to species is given, and a description, figures, and range map are presented for each species. Some new descriptive terminology is introduced for the male genitalia. The male median lobe is described and illustrated for the first time for each species. Adults of the viduatus species-group appear to be associated with the plant genus Hypericum L. (Clusiaceae).