Rossmaessleria scherzeri was named as a new species from Gibraltar in 1867, then cited repeatedly and illustrated in the literature up to 1904. Subsequently, except for passing mentions in 1976 and 1982 it has usually been overlooked, resulting in its omission from local and European lists of threatened species. In 2006 it was dismissed as a dubious taxon, probably synonymous with Iberus marmoratus. We report the “rediscovery” of the species at Gibraltar in 2015 and redescribe and illustrate it, showing differences from Iberus marmoratus (with which it coexists) and giving the first account of its genital anatomy, which reaffirms the generic allocation. The genus has otherwise been known from nine taxa restricted to NW. Morocco, from which the genital anatomy has been described for three taxa. In addition, we provide the first descriptions of the genitalia of R. olcesei, redescribe its shells, report additional localities and comment on variation in its shell characters.