The thread-legged bug genus Onychomesa Wygodzinsky 1966 (Hemiptera: Reduviidae: Emesinae: Emesini, formerly Metapterini) and its three described species are reviewed. The Sri Lankan species Ischnonyctes alatus Distant 1903 is resurrected from the synonymy with Schidium marcidum (Uhler, 1896) and transferred to Onychomesa, and O. susainathani Wygodzinsky, 1966 is considered a junior synonym of this species, resulting in the following taxonomic changes: O. alata (Distant 1903), stat. rev. et comb. nov. = O. susainathani Wygodzinsky 1966, syn. nov. The lectotype of I. alatus is designated. A new species, O. schuhi Chen et Cai, sp. nov., is described from Hainan Island, southern China. An updated key to the species of Onychomesa is provided.
The species is registered in ZooBank (http://zoobank.org/8F582127-631F-4CD9-9E02-C3CD14AA52DC).
