†Placodermi McCoy, 1848 †Arthrodira Woodward, 1891 †Brachythoraci Gross, 1932 1 Genus †Holonema Newberry, 1890 2.1 Genus †Homostius Asmuss, 1856 2.2.1 Genus †Buchanosteus Stensiö, 1945 2.2.2 †Eubrachythoraci Miles, 1971