Tricleidus is a cryptoclidid from the Oxford Clay Formation of the UK. The holotype specimen (NHMUK R 3539) consists of disarticulated elements including most of skull and half the postcranium, from the Kosmoceras jasoni – Peltoceras athleta zones from the lowest deposits of the Oxford Clay Formation. The type and only species of Tricleidus is T. seeleyi.
Persson (1962) erected the new species ‘Tricleidus‘ svalbardensis, but this species reallocated to Colymbosaurus (Knutsen et al. 2012a).
