A new genus, Paridiagonum, with the new species, Patidiagonum bidentatum, and a new species of Fortagonum Darlington, 1952, Fortagonum bellorum, are described from Mt. Misim in the vicinity of Wau, central eastern Papua New Guinea. The new genus in body shape is similar to the genus Idiagonum Darlington, 1952, but is distinguished from that genus by absence of setae at the prosternal intercoxal process, presence of three discal punctures on the elytra, bidentate apex of each elytron, deeply excised fourth tarsomeres, and much shorter and wider female gonocoxites 2, which lack the dorso-median ensiform seta. Structure of the fourth tarsomeres, however, suggests relationships with some species described by Darlington (1952) as belonging to Colpodes Macleay (e.g., Colpodes antedens Darlington, 1952, and Colpodes acuticauda Darlington, 1952). The new species of Fortagonum is distinguished from all described species by a combination of characters: chaetotaxy of head, pronotum, and elytra; distinctly fusiform shape of pronotum; rather triangular shape of the unarmed elytra; and structure of the aedeagus.