The species "Cetiosaurus longus", named in 1842 by Owen, was referred to the genus "Cetiosauriscus" without comment by sauropod palaeontologist John Stanton McIntosh in 1990. The species was named for a dorsal and caudal vertebrae from the Portland Stone of Garsington, Oxfordshire (both now missing) and two other caudal vertebrae from the same deposit of nearby Thame. Owen also referred a single vertebra and some metatarsals originally named "Cetiosaurus epioolithicus" (an invalid "nomen nudum") to the species. One of the vertebrae (OUMNH J13871) may instead be a cervical, as it has one mildly convex and one concave articular face. Characterised as having uniquely elongate vertebral centra (body of the vertebra), "C. longus" is not a diagnostic taxon. As it lacks any diagnostic features of "Cetiosauriscus", the species should be referred to by its original designation, "Cetiosaurus longus".