The Collaborative International Dictionary of English v.0.48:

Cephalaspis \Ceph`a*las"pis\, n. [NL., fr. Gr. kefalh` head + ?
   a shield.] (Paleon.)
   A genus of fossil ganoid fishes found in the old red
   sandstone or Devonian formation. The head is large, and
   protected by a broad shield-shaped helmet prolonged behind
   into two lateral points.
   [1913 Webster]