Opinions from D. S. Brown 1981
- 'Apractocleidus is an objective synonym of Cryptoclidus'
- 'Apractocleidus teretipes is a subjective synonym of Cryptoclidus eurymerus'
- 'Aristonectes belongs to Cryptoclididae'
- 'Cimoliosaurus is a misspelling of Cimoliasaurus'
- 'Cimoliosaurus durobrivensis is recombined as Tremamesacleis durobrivensis' according to White 1940
- 'Tremamesacleis durobrivensis is a subjective synonym of Muraenosaurus leedsii'
- 'Cimoliosaurus durobrivensis is a misspelling of Cimoliasaurus durobrivensis'
- 'Cimoliosaurus plicatus is a subjective synonym of Muraenosaurus leedsii'
- 'Cimoliosaurus richardsoni is recombined as Cryptoclidus richardsoni'
- 'Colymbosaurus belongs to Elasmosauridae'
- 'Cryptoclididae belongs to Plesiosauroidea'
- 'Elasmosauridae belongs to Plesiosauroidea'
- 'Elasmosaurus belongs to Elasmosauridae'
- 'Kimmerosaurus belongs to Cryptoclididae'
- 'Kimmerosaurus langhami belongs to Kimmerosaurus'
- 'Muraenosaurus belongs to Elasmosauridae'
- 'Muraenosaurus (Cryptoclidus) was reranked as Cryptoclidus and belongs to Cryptoclididae'
- 'Cryptoclidus platymerus is a subjective synonym of Cryptoclidus eurymerus'
- 'Muraenosaurus beloclis belongs to Muraenosaurus'
- 'Cimoliasaurus brevior is a nomen dubium'
- 'Muraenosaurus leedsi is a misspelling of Muraenosaurus leedsii'
- 'Muraenosaurus leedsii belongs to Muraenosaurus'
- 'Muraenosaurus platyclis is a subjective synonym of Muraenosaurus leedsii'
- 'Muraenosaurus platyclis is recombined as Tremamesacleis platycleis' according to White 1940
- 'Picrocleidus is a subjective synonym of Muraenosaurus'
- 'Plesiosauria belongs to Sauropterygia'
- 'Plesiosauridae belongs to Plesiosauroidea'
- 'Plesiosauroidea belongs to Plesiosauria'
- 'Plesiosaurus belongs to Plesiosauridae'
- 'Plesiosaurus affinis is a nomen dubium'
- 'Plesiosaurus brachistospondylus is a nomen dubium'
- 'Plesiosaurus brevis belongs to Plesiosaurus' according to Owen 1854
- 'Plesiosaurus brevis is a nomen dubium'
- 'Plesiosaurus carinatus belongs to Plesiosaurus' according to Phillips 1871
- 'Plesiosaurus carinatus is replaced by Plesiosaurus phillipsi'
- 'Plesiosaurus doedicomus is a nomen dubium'
- 'Plesiosaurus durobrivensis belongs to Plesiosaurus' according to Seeley 1892
- 'Plesiosaurus durobrivensis is a subjective synonym of Cryptoclidus eurymerus'
- 'Plesiosaurus ellipsospondylus belongs to Plesiosaurus' according to Phillips 1871
- 'Plesiosaurus ellipsospondylus is a nomen dubium'
- 'Plesiosaurus eurymerus is recombined as Cryptoclidus eurymerus'
- 'Plesiosaurus hexagonalis is a nomen dubium'
- 'Plesiosaurus infraplanus is a nomen dubium'
- 'Plesiosaurus levis belongs to Plesiosaurus' according to Owen 1854
- 'Plesiosaurus levis is a nomen dubium'
- 'Plesiosaurus manselii is a subjective synonym of Colymbosaurus trochanterius'
- 'Plesiosaurus manseli is a misspelling of Plesiosaurus manselii'
- 'Colymbosaurus megadeirus is a subjective synonym of Colymbosaurus trochanterius'
- 'Plesiosaurus megadirus is a misspelling of Plesiosaurus megadeirus'
- 'Plesiosaurus megapleuron belongs to Plesiosaurus' according to Owen 1854
- 'Plesiosaurus megapleuron is a nomen dubium'
- 'Plesiosaurus oxfordiensis is a nomen nudum'
- 'Plesiosaurus oxoniensis is a nomen dubium'
- 'Plesiosaurus phillipsi is a nomen dubium'
- 'Plesiosaurus planispondylus belongs to Plesiosaurus' according to Damon 1860
- 'Plesiosaurus planispondylus is a nomen nudum'
- 'Muraenosaurus plicatus is a subjective synonym of Muraenosaurus leedsii'
- 'Plesiosaurus subdepressus is a nomen nudum'
- 'Plesiosaurus trochanterius is recombined as Colymbosaurus trochanterius'
- 'Plesiosaurus truncatus is recombined as Muraenosaurus truncatus' according to Sauvage 1911
- 'Plesiosaurus truncatus is a nomen dubium'
- 'Plesiosaurus validus is a nomen dubium'
- 'Plesiosaurus winspitensis is a nomen dubium'
- 'Pliosauridae belongs to Pliosauroidea'
- 'Pliosauroidea belongs to Plesiosauria'
- 'Pliosaurus portlandicus is a subjective synonym of Colymbosaurus trochanterius'
- 'Sauropterygia was reranked as a subclass and belongs to Reptilia'
- 'Sthenarosaurus belongs to Plesiosauroidea'
- 'Tremamesacleis is a subjective synonym of Muraenosaurus'
- 'Tricleidus belongs to Elasmosauridae'
- 'Tricleidus seeleyi belongs to Tricleidus'