Re-examination of the holotype of Dermacentor atrosignatus Neumann, 1906 (Acari: Ixodidae) stored in the Natural History Museum (London, UK) revealed that this taxon is identical with D. auratus Supino, 1897 and should be treated as a junior synonym of the latter species. A correct name for the distinct species previously identified as D. atrosignatus Neumann, 1906 sensu Wassef & Hoogstraal, 1984 should be D. tricuspis (Schulze, 1933) n. comb., n. stat. Adults of D. tricuspis are redescribed here. Re-examination of extensive holdings of Oriental Dermacentor Koch, 1844 ticks stored in the United States National Tick Collection revealed that a morphologically distinct new species of this genus, namely D. falsosteini D. Apanaskevich, M. Apanaskevich & Nooma n. sp. should be recognized. Adults of D. tricuspis and D. falsosteini n. sp. can be distinguished from other species of Oriental Dermacentor and each other by the colour pattern of the conscutum and scutum, the pattern of punctations on the pseudoscutum and scutum, the shape of female genital structures and spurs on coxa I. Dermacentor tricuspis is recorded from Indonesia, Malaysia, the Philippines and Thailand where the adults were mostly collected from various species of wild pigs (Artiodactyla: Suidae) and vegetation; few adults were available from other mammals (Artiodactyla: Bovidae; Carnivora: Canidae, Felidae, Ursidae; Pholidota: Manidae), as well as humans and reptiles (Squamata: Elapidae, Varanidae). One male was reared from a nymph collected on a rodent (Rodentia: Muridae). Dermacentor falsosteini n. sp. is found in Indonesia, Malaysia and Thailand where the adults were collected from bearded pig, Sus barbatus Müller, wild boar, S. scrofa Linnaeus, unidentified wild pig, Sus sp. (Artiodactyla: Suidae), Malayan tapir, Tapirus indicus Desmarest (Perissodactyla: Tapiridae), human and vegetation.