The large genus Orthomorpha is rediagnosed and is shown to currently comprise 51 identifiable species ranging from northern Myanmar and Thailand in the Northwest to Lombok Island, Indonesia in the Southeast. Of them, 20 species have been revised and/or abundantly illustrated, based on a restudy of mostly type material; further 12 species are described as new. The type-species O. beaumontii (Le Guillou, 1841) is redescribed in due detail from male material as well, actually being a senior subjective synonym of O. spinala (Attems, 1932), syn. n. Two additional new synonymies are proposed.
All species have been keyed and all new and some especially widespread species have been mapped. Further six species, including two revised from type material, are still to be considered dubious, mostly because their paraterga appear to be too narrow to represent Orthomorpha species. A new genus, Orthomorpchoices gen. n., diagnosed versus Orthomorpha through only moderately well developed paraterga, coupled with a poorly bi- or trilid gonopod tip, with at least some of its apical prongs being short spines, is erected for two species: O. setasus (Attems, 1937), the type-species, which is also revised from type material, and O. exaratus (Attems, 1953), both comb. n. ex Orthomorpha.