In 1980, Charig described a specimen of indeterminate diplodocid from the Early Cretaceous of England, and re-examined the holotype of "Cetiosauriscus leedsii" to compare its characteristics. In this publication he confirmed that the ilium of the holotype of "C. leedsii", NHMUK R1988, was too incomplete to be compared to the also incomplete ilium of the referred specimen NHMUK R3078. Because of the lack of overlap the referral of NHMUK R3078 to "Cetiosauriscus leedsii" was no longer verifiable, so Charig named the new species "Cetiosauriscus stewarti" for NHMUK R3078. The specific name was chosen to honour Sir Ronald Stewart, the chairman of the London Brick Company that owned the clay pit the fossils had been found in. Furthermore, Charig considered "Cetiosauriscus leedsii" and "Cetiosauriscus greppini" to be dubious taxa, making "C. stewarti" the only valid species within "Cetiosauriscus". Because of the invalidity of the type species "C. leedsii", Charig made a petition to the International Code of Zoological Nomenclature (ICZN) in 1993 to designate "Cetiosauriscus stewarti" as the type species of its genus, being the taxon containing the specimen Huene had originally named the genus for and distinguished from "Cetiosaurus", and also a taxonomically more stable name. This was accepted by the ICZN in 1995, making "Cetiosauriscus stewarti" the type species of "Cetiosauriscus". The only specimen that can confidently be assigned to "C. stewarti" is the holotype NHMUK R3078, although it is possible that isolated teeth from the Oxford Clay could be from the taxon.