Abstract The white gypsum dune ecosystem in the Tularosa Basin in south central New Mexico is the largest gypsum dune field on earth, covering 712.25 km2. White Sands National Monument in Otero County, New Mexico, protects approximately 40%, 297.85 km2, of this dune field. In 2006 the US National Park Service initiated a long term study of the Lepidoptera at White Sands National Monument, resulting in the discovery of two new species, Euxoa lafontainei Metzler & Forbes, n. sp. and Protogygia whitesandsensis Metzler & Forbes, n. sp. described herein. Adult moths and male and female genitalia are illustrated for Euxoa lafontainei, and adults and male genitalia are illustrated for Protogygia whitesandsensis and its relatives.