Source : Webster's Revised Unabridged Dictionary (1913)

Placodermi \Plac`o*der"mi\, n. pl. [NL., fr. Gr. ?, ?, a tablet
   + ? skin.] (Paleon.)
   An extinct group of fishes, supposed to be ganoids. The body
   and head were covered with large bony plates. See Illust.
   under {Pterichthys}, and {Coccosteus}.

Source : WordNet®

Placodermi
     n : extinct group of bony-plated fishes with primitive jaws
         [syn: {class Placodermi}]