Source : Webster's Revised Unabridged Dictionary (1913)

Ichthyosauria \Ich`thy*o*sau"ri*a\, n. pl. [NL. See
   {Ichthyosaurus}.] (Paleon.)
   An extinct order of marine reptiles, including Ichthyosaurus
   and allied forms; -- called also {Ichthyopterygia}. They have
   not been found later than the Cretaceous period.

Source : WordNet®

Ichthyosauria
     n : extinct marine reptiles: ichthyosaurs [syn: {order
         Ichthyosauria}]