The true identity of the scorpion Scorpio (Atreus) obscurus Gervais, 1843 is discussed based on new data. The original type material was recently discovered in the collections of the Muséum national d’Histoire naturelle in Paris, which confirms that this old species, originally described by Gervais based on two female specimens from French Guiana, does indeed belong to the genus Tityus C. L. Koch, 1836. Furthermore, an analysis of all morphological characteristics of Tityus (Atreus) obscurus verifies its position as a senior synonym of both Tityus paraensis Kraepelin, 1896 and Tityus cambridgei Pocock, 1897. In this paper, we designate the two female syntypes of Scorpio (Atreus) obscurus as a female lectotype and a female paralectotype for Tityus (Atreus) obscurus (Gervais, 1843), and synonymize Tityus paraensis Kraepelin, 1896 with Tityus obscurus (Gervais, 1843).