A new species, Cnestusquadrispinosus, is described from Thailand, Brunei Darussalam, and East Malaysia (Sabah). It is compared to three related species of Cnestus which lack a mycangial tuft of hairs on the pronotum, and have an impressed elytral declivity.
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.
Four new species, Arixyleborus halabala Sittichaya, Beaver & Smith sp. nov., Arixyleborus longicauda Sittichaya, Beaver & Smith sp. nov., Arixyleborus vellus Sittichaya, Beaver & Smith sp. nov. are described from Thailand, and Arixyleborus liratus Sittichaya, Beaver & Smith sp. nov. from Thailand and East Malaysia (Sabah). With the inclusion of the species described here, the diversity of Arixyleborus is increased to 46 species, of which 20 occur in Thailand. A synoptic list with distributions and habitat types is provided.