The Collaborative International Dictionary of English v.0.48:

Ostracodermi \Os`tra*coder"mi\, prop. n. pl. [NL., fr. Gr.
   'o`strakon shell of a testacean + ? skin.] (Zool.)
   A suborder of fishes of which Ostracion is the type.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Ostracodermi
    n 1: extinct group of armored jawless vertebrates; taxonomy is
         not clear [syn: Ostracodermi, order Ostracodermi]