Rianilaneuria diminuta Pescador & Peters, a new genus and species from the mideastern slopes of Madagascar, is described from male and female adults and eggs. The adults are defined by the presence of vein IR and the absence of vein IMP in the forewing; male genitalia with two-segmented forceps, short penes and a small truncate styliger; absence of mesoscutellar filaments; and elongate coxae. The egg chorion is adorned with widely spaced and circularly clustered sponge-like microsetae.