As a result of the first phylogenetic analysis of the Mecocephala group, Hypanthracos Grazia & Campos, 1996 is included to the Mecocephala group; H . meridionalis is redescribed, and four new species in three new genera are described: the genus Chimerocoris gen.n. is proposed to accommodate C . luridus sp.n., the genus Liscocephala gen.n. is proposed to accommodate L . fumosa sp.n. and the genus Triunfus gen.n. is proposed to accommodate two new species: T . carvalhoi sp.n. and T . incarnatus sp.n. The new taxa are distributed in Brazil and Uruguay. In addition, Ogmocoris Mayr, 1864 is redescribed, a lectotype is designated, and the genitalia of both sexes for O .  hypomelas (Burmeister) are described for the first time. The standard terminology for the male genitalia of members of the Mecocephala group is proposed. Photographs, illustrations, and a distribution map are also provided for all the species.