A re-description and a re-classification is made for the plesiosaur specimen PMO A 27745 previously identified in 1962 as Tricleidus svalbardensis Persson. In all probability the fossil is from the Slottsmøya Member of the Agardhfjellet Formation and was collected at the entrance to Sassenfjorden, Svalbard. Its age is Volgian. Study of the material, in reference to the current taxonomy of the Plesiosauria which acknowledges the Polycotylidae as part of the Plesiosauria, suggests that it may belong to the Tricleidia of the Superfamily Cryptocleidoidea. A cladistic analysis of related taxa places Tricleidus svalbardensis in a close relationship with Polycotylus, Dolichorhynchops and Tricleidus. The distal part of the fossil is preserved, from the pelvic girdle backwards with dorsal, sacral, and caudal vertebrae present, along with two ischia, two pubes and two flippers of which the right is almost complete. Some rib fragments are also preserved. A catalogue has been made of all available Jurassic and Cretaceous marine vertebrate material from Svalbard containing three plesiosaur propodials and epipodials, a plesiosaur ilium, a large ichthyosaurian humerus and a few plesiosaur teeth.