plesiosauria

from WordNet (r) 3.0 (2006)

Plesiosauria
    n 1: any of the plesiosaurs [syn: {Plesiosauria}, {suborder
         Plesiosauria}]

from The Collaborative International Dictionary of English v.0.48

Plesiosauria \Ple`si*o*sau"ri*a\, n. pl. [NL. See
   {Plesiosaurus}.] (Paleon.)
   An extinct order of Mesozoic marine reptiles including the
   genera Plesiosaurus, and allied forms; -- called also
   {{Sauropterygia}}.
   [1913 Webster]