The lancanjiang species group of the termitophilous ground beetle genus Orthogonius Macleay, 1825, is defined and reviewed. This group is characterized by the black and rather elongate body, dense punctation on head and elytra, long and slender appendages, thin fore tibiae, and elytral interval 3 without a subapical setiferous pore. To date, the lancanjiang species group is composed of four species and one subspecies, including three new species and one new subspecies which are described in the present paper: O. macrophthalmus sp. n. (northern Vietnam), O. euthyphallus sp. n. (southern Vietnam), O. euthyphallus bolavenensis ssp. n. (southern Laos) and O. carinatus sp. n. (northern Laos). A distribution map and a key to all species of this group are also provided.
Keywords: Carabidae; Coleoptera; Oriental; Orthogoniini; Orthogonius; taxonomy.