The southwestern Atlantic Stingray Dasyatis macrophthalma Gomes, Rosa, and Gadig was described under two different names which appeared in the original publication by mistake. By using the First Reviser principle, according to the provisions of the International Code of Zoological Nomenclature, we select Dasyatis marianae as the valid name for the species. The name D. macrophthalma previously had been published by other authors in its homonym form D. macrophtalma, without reference to a formal description (a nomen nudum). It is herein treated as the junior objective synonym of D. macrophthalma. To avoid the repetition of similar cases, we recommend the authors preparing descriptions of new taxa refrain from publicizing manuscript names in the Web, scientific meetings, news media, or museum labels.