Ichthyosaurus

‖Ich′thy‐o‐sau″rus (?), n.; pl.Ichthyosauri (#). [NL., fr. Gr. ιχθὔσ, -ύοσ, a fish + σαυ̑ροσ a lizard.] (Paleon.) An extinct genus of marine reptiles; — so named from their short, biconcave vertebræ, resembling those of fishes. Several species, varying in length from ten to thirty feet, are known from the Liassic, Oölitic, and Cretaceous formations.