Opinions from S. W. Williston 1903
- 'Brachauchenius belongs to Pliosauridae'
- 'Brimosaurus belongs to Plesiosauria'
- 'Brimosaurus grandis belongs to Brimosaurus'
- 'Cimoliasaurus belongs to Plesiosauria'
- 'Cimoliasaurus laramiensis belongs to Cimoliasaurus'
- 'Cimoliosaurus magnus is recombined as Cimoliasaurus magnus'
- 'Cimoliosaurus snowii is recombined as Cimoliasaurus snowii'
- 'Discosaurus is a subjective synonym of Cimoliasaurus'
- 'Discosaurus planior is recombined as Cimoliasaurus planior'
- 'Discosaurus vetustus is recombined as Cimoliasaurus vetustus'
- 'Dolichorhynchops belongs to Plesiosauria'
- 'Dolichorhynchops osborni belongs to Dolichorhynchops'
- 'Elasmosaurus belongs to Plesiosauria'
- 'Elasmosaurus intermedius belongs to Elasmosaurus'
- 'Elasmosaurus orientalis belongs to Elasmosaurus'
- 'Elasmosaurus platyurus belongs to Elasmosaurus'
- 'Elasmosaurus serpentinus belongs to Elasmosaurus'
- 'Embaphias belongs to Plesiosauria'
- 'Embaphias circulosus belongs to Embaphias'
- 'Megalneusaurus belongs to Plesiosauria'
- 'Nothosaurops belongs to Plesiosauria'
- 'Nothosaurops occiduus belongs to Nothosaurops'
- 'Oligosimus belongs to Plesiosauria'
- 'Oligosimus grandaevus belongs to Oligosimus'
- 'Orophosaurus belongs to Plesiosauria'
- 'Orophosaurus pauciporus belongs to Orophosaurus'
- 'Pantosaurus belongs to Plesiosauria'
- 'Parasaurus striatus is recombined as Pantosaurus striatus'
- 'Piptomerus belongs to Plesiosauria'
- 'Piptomerus hexagonus belongs to Piptomerus'
- 'Piptomerus megaloporus belongs to Piptomerus'
- 'Piptomerus microporus belongs to Piptomerus'
- 'Piratosaurus belongs to Plesiosauria'
- 'Piratosaurus plicatus belongs to Piratosaurus'
- 'Plesiosaurus belongs to Plesiosauria'
- 'Plesiosaurus brevifemur belongs to Plesiosaurus'
- 'Plesiosaurus gouldii belongs to Plesiosaurus'
- 'Plesiosaurus gulo belongs to Plesiosaurus'
- 'Plesiosaurus lockwoodii is recombined as Taphrosaurus lockwoodii'
- 'Plesiosaurus mudgei belongs to Plesiosaurus'
- 'Plesiosaurus shirleyensis belongs to Plesiosaurus' according to Knight 1900
- 'Pliosauridae belongs to Plesiosauria'
- 'Polycotylus belongs to Plesiosauria'
- 'Polycotylus ischiadicus belongs to Polycotylus'
- 'Polycotylus latipinnis belongs to Polycotylus'
- 'Taphrosaurus belongs to Plesiosauria'
- 'Trinacromerum belongs to Plesiosauria'
- 'Trinacromerum bentonianum belongs to Trinacromerum'
- 'Uronautes belongs to Plesiosauria'
- 'Uronautes cetiformis belongs to Uronautes'