‖n.; pl. Ichthyosauri [ NL., fr. Gr. 'ichqy`s, -y`os, a fish + say^ros 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. [ 1913 Webster ]