ostracophori

from The Century Dictionary.

• A division of fishes, commonly regarded as a subclass, containing extinct species whose remains, are found from the Silurian to the Lower Carboniferous. Jaws, a segmented backbone, and limb-arches are wanting, and the head and front part of the body are protected by bony plates. The term is in common use, though antedated by Aspidoganoidei.