The purpose of this application, under Article 81.1 of the Code, is to preserve stability in the taxonomy of sauropod dinosaurs by designating Cetiosaurus oxoniensis as the type species of Cetiosaurus. The genus Cetiosaurus (including the species C. medius and C. oxoniensis) was established during the earliest period of research on sauropod dinosaurs, and is historically significant. The name Cetiosaurus was fixed to the type species Cetiosaurus medius, a sauropod of indeterminate affinities; however, the fragmentary nature of the type material of C. medius, combined with the subsequent description of much more complete Middle Jurassic sauropod material as Cetiosaurus oxoniensis, has meant that subsequent literature has overwhelmingly adopted C. oxoniensis over C. medius as the primary exemplar of Cetiosaurus. Stability would be best served by designating Cetiosaurus oxoniensis as the type species of the genus Cetiosaurus in place of the current type species, C. medius.