The Collaborative International Dictionary of English v.0.48:

Rhynchocephala \Rhyn`cho*ceph"a*la\, n. pl. [NL., fr. Gr.
   "ry`gchos snout + kefalh` head.] (Zool.)
   An order of reptiles having biconcave vertebrae, immovable
   quadrate bones, and many other peculiar osteological
   characters. Hatteria is the only living genus, but numerous
   fossil genera are known, some of which are among the earliest
   of reptiles. See Hatteria. Called also Rhynchocephalia.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Rhynchocephalia
    n 1: tuataras; extinct forms from middle Triassic [syn:
         Rhynchocephalia, order Rhynchocephalia]