The Collaborative International Dictionary of English v.0.48:

Sauropterygia \Sau*rop`te*ryg"i*a\, n. pl. [NL., fr. Gr. ? a
   lizard + ?, ?, a wing.] (Paleon.)
   Same as Plesiosauria.
   [1913 Webster]

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]

WordNet (r) 3.0 (2006):

Sauropterygia
    n 1: extinct marine reptiles: plesiosaurs; nothosaurs [syn:
         Sauropterygia, order Sauropterygia]