The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ichthyopterygia \Ich`thy*op`te*ryg"i*a\, n. pl. [NL. See
   Ichthyopterygium.] (Paleon.)
   See Ichthyosauria.
   [1913 Webster]