A.C. Buller (1868) described Argyrophorus williamsianus nov., on one specimen collecled by CharlesDarwin at “Port Famine", Strail of Magellan. Most Chilean and European Lepidopterologisls for ihepast 100 years have noi properlv recognized this species, although E. Creta in this Catalogue (1965)memions it as present from “Nuble (Termas de Chillán) down lo Pon Famine (Strait of Magellan)''.J. Herrera (1962) during his visit to the British Museum (Natural History) had the privilege toexamine all the material of this species kept there, and except for the Darwin's examplc coming fromPon Famine, all the resl were collected from cióse argentinian localities. In his paper J. Herreradescribed a new genus, Stuardosatyrus, to hold Butler's species, under which new combination it is nowreferred to.Professor Vicente Pérez D'A, from 1981 on, has collected abnut 30 specimens of both sexes allcoming from “Planicies Orientales" with coid climate steppe (BSk’). in actual Chilean lerritorv.The female genitalia of S. williamsianus (Butler) is herein described and illuslrated for the First time,as wcll as the wing venalion and genitalia of cióse allied genera lo which williamsianus has often beassigned to.Photographs of S. williamsianus and of the types ol Etchevemus chiliensis magallamrus Herrera, are alsoincluded.