†Placodermi McCoy, 1848
   †Arthrodira Woodward, 1891
     †Brachythoraci Gross, 1932
       1 Genus †Holonema Newberry, 1890
       2.1 Genus †Homostius Asmuss, 1856
       2.1.0 [Genus †Homotius Carr & Hlavin, 2010] see Genus Homostius Asmuss, 1856
       2.2.1 Genus †Buchanosteus Stensiö, 1945
       2.2.2 †Eubrachythoraci Miles, 1971