aspidocephali

Century Dictionary and Cyclopedia

1. A Paleozoic order of singular ostracoderm fishes. They have a large, heavily plated head-shield composed of three layers; orbits close together; body, in the typical genera, covered with quadrangular scales; no paired fins; and heterocercal tail. The best-known of these forms is Cephalaspis. The species have been found only in the Upper Silurian beds of Great Britain and the Baltic provinces and in the Old Red Sandstone.