Apidaurus, a neotropical alydine genus, is revised. Apidaurus conspersus Stål is redescribed and Apidaurus triguttatus Berg synonymized with it (new synonymy); Apidaurus longitylus Schaefer and Schaffner new species is described, and the two species are keyed. The fifth instar of A. conpsersus is briefly described. The genital capsule of Apidaurus is also described, and its homologies with structures of other alydine genital capsules are discussed. Apidaurus conspersus occurs from southern Texas into southern Brazil, and A. longitylus from French Guiana into Brazil; the two species overlap in Paraguay. The phylogenetic relationships of the genus, and of the two species, are discussed.