Cyprinids belonging to the genus Dionda have a relatively broad distribution in southwestern North America. However, validity of populations in several of the nominal species has not been examined rigorously. During the course of a conservation-genetics study of Dionda in western Texas we determined that one population presumed to represent Dionda episcopa instead belongs to Dionda argentosa. This extends the native range of D. argentosa to include the lower Pecos River basin in addition to its currently recognized distribution in three tributaries of the Rio Grande. Conservation implications for both species are discussed.