The Collaborative International Dictionary of English v.0.48:

Holocephali \Hol`o*ceph"a*li\, n. pl. [NL., from Gr. "o`los
   whole + kefalh` head.] (Zool.)
   An order of elasmobranch fishes, including, among living
   species, only the chim[ae]ras; -- called also Holocephala.
   See Chim[ae]ra; also Illustration in Appendix.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Holocephali
    n 1: chimaeras and extinct forms [syn: Holocephali, subclass
         Holocephali]