What is "cephalaspis"

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] ||

Cephalaspis (head shield) was a genus in the class Osteostraci of Palaeozoic armoured jawless fishes, or ostracoderms. It was a medium-sized detritivorous fish that lived in freshwater streams and estuaries of the early Devonian.