The Collaborative International Dictionary of English v.0.48:

Hatteria \Hat*te"ri*a\ (h[a^]t*t[=e]"r[i^]*[.a]), n. [NL.]
   (Zool.)
   A New Zealand lizard, which, in anatomical character, differs
   widely from all other existing lizards. It is the only living
   representative of the order Rhynchocephala, of which many
   Mesozoic fossil species are known; -- called also
   Sphenodon, tuatara, and Tuatera.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sphenodon \Sphe"no*don\, n. [Gr. sfh`n a wedge + ???, ???, a
   tooth.] (Zool.)
   Same as Hatteria.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Sphenodon
    n 1: coextensive with the order Rhynchocephalia: tuataras [syn:
         Sphenodon, genus Sphenodon]