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: Orthomorpha atypicasp. n., Orthomorpha communissp. n., Orthomorpha isarankuraisp. n., Orthomorpha picturatasp. n., Orthomorpha similanensissp. n., Orthomorpha suberectasp. n., Orthomorpha tuberculiferasp. n.,Orthomorpha subtuberculiferasp. n. and Orthomorpha latitergasp. n., all from Thailand, as well as Orthomorpha elevatasp. n.,Orthomorpha spiniformissp. n. and Orthomorpha subelevatasp. n., from northern Malaysia. The type-species Orthomorpha beaumontii (Le Guillou, 1841) is redescribed in due detail from male material as well, actually being a senior subjective synonym of Orthomorpha spinala (Attems, 1932), syn. n. Two additional new synonymies are proposed: Orthomorpha rotundicollis (Attems, 1937) = Orthomorpha tuberculata (Attems, 1937), syn. n., and Orthomorpha butteli Carl, 1922 = Orthomorpha consocius Chamberlin, 1945, syn. n., the valid names to the left. 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, Orthomorphoidesgen. n., diagnosed versus Orthomorpha through only moderately well developed paraterga, coupled with a poorly bi- or trifid gonopod tip, with at least some of its apical prongs being short spines, is erected for two species: Orthomorpha setosus (Attems, 1937), the type-species, which is also revised from type material, and Orthomorpha exaratus (Attems, 1953), both comb. n. ex Orthomorpha.
The genus Antheromorpha is redefined and shown to comprise 11 valid species: Antheromorpha miranda (Pocock, 1895), Antheromorpha bistriata (Pocock, 1895), Antheromorpha comotti (Pocock, 1895), Antheromorpha festiva (Brölemann, 1896), Antheromorpha harpaga (Attems, 1937), Antheromorpha mediovirgata (Carl, 1941), Antheromorpha minlana (Pocock, 1895), Antheromorpha pardalis (Pocock, 1895), Antheromorpha paviei (Brölemann, 1896), comb. n., Antheromorpha rosea Golovatch, 2013 and Antheromorpha uncinata (Attems, 1931). Three new synonymies are proposed: Antheromorpha bivittata (Pocock, 1895) and Antheromorpha melanopleuris (Pocock, 1895) are synonymized under Antheromorpha miranda (Pocock, 1895), and Antheromorpha orophila (Carl, 1941) under Antheromorpha comotti (Pocock, 1895). Detailed descriptions and illustrations of fresh material from Thailand and Malaysia are given, especially regarding colour patterns which appear to be crucial for accurate species identifications. Two Antheromorpha species proposed by Attems are redescribed, based on type material. The genus is rediagnosed and a key and a distribution map are also provided. At least in Thailand, adult Antheromorpha rosea have been found to occur every year only for one or two weeks in September or October, disappearing thereafter.
The millipede genus Malayorthomorpha Mršić, 1996, so far monospecific and previously known only from Park Belum, Perak State, northern Malaysia, is recorded from a mountain in Betong District, Yala Province, southern Thailand for the first time, being represented there by two new species: M.halabala sp. nov. and M.hulutbeeda sp. nov. Both new species are found to occur syntopically and can be assumed as narrowly endemic to the Titiwangsa Mountain Range which begins in southern Thailand, crosses the Malaysian border, and extends into east and west coast regions of the Malay Peninsula. In addition, the generic diagnosis is slightly updated, and a key to all three species is provided.