A new species of the genus Vilcunia from near Lago Belgrano, 47°50' South latitude, Santa Cruz, Argentina, is described. The morphology of the new species, V. periglacialis sp. nov. and the closely related V. silvanao are compared and a redescription of V. silvanae is made. Both species are of biogeographical interest given their distribution in the basaltic mesetas of the slopes of the Patagonian Andes.Material digitalizado en SEDICI gracias a la colaboración del Dr. Jorge Williams (FCNM-UNLP).Facultad de Ciencias Naturales y Museo