What is 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 called?

cephalaspis — 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. (Webster's 1913.)

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