The purpose of this application, under Article 81.1 of the Code, is to preserve stability in the taxonomy of stegosaurian dinosaurs by replacing Stegosaurus armatus Marsh, 1877, the unidentifiable type species of the ornithischian dinosaur genus Stegosaurus Marsh, 1877, with the very well represented nominal species Stegosaurus stenops Marsh, 1887, also from the Upper Jurassic Morrison Formation, U.S.A. This genus is the basis for Stegosauria Marsh, 1877, stegosauroidea Marsh, 1880, stegosauridae Marsh, 1880 and stegosaurinae Marsh, 1880. Maidment et al. (2008) listed seven putative autapomorphic characters for Stegosaurus and five for the species Stegosaurus armatus in its current usage. However, the holotype of S. armatus, which consists of an articulated series of 18 incomplete vertebrae from the proximal half of the tail and a very large but incomplete dermal plate, shows none of these diagnostic characters and so S. armatus must be considered a nomen dubium. However, the holotype of S. stenops Marsh, 1887 shares all 12 autapomorphies with S. armatus in its current usage, being based on an almost complete skeleton (USNM 4934), most of it still in the rock preserving almost natural articulation, which would make S. stenops by far the best available species to replace S. armatus as type species of Stegosaurus Marsh, 1877.