It has also been named Ichthyosaurus trigonus posthumus, and identified with Macropterygius and Brachypterygius extremus.
Many specimens have been referred to Ichthyosaurus trigonus; Bauer (1898) suggested that – what are now – Ophthalmosaurus, Brachypterygius and Nannopterygius should be synonymised into Ichthyosaurus trigonus, as this is the older name.