COPE,1 by combining the modifications of the quadrate and supporting bones with the characters used by Huxley, further developed Owen's classification, separating the Cope. Pythonomorpha and Rhynchocephalia as distinct orders from the Lacertilia. He eventually2 elaborated the following classification, based entirely on osteological characters: I. The quadrate bone immovably fixed to the adjacent elements by suture. A. Scapular arch external to ribs; temporal region with a complex bony roof ; no longitudinal postorbital bars. A tabular and supramastoid bones and a presternum; limbs ambulatory; vertebrae amphicoelous. Order 1, COTYLOSAURIA. ,SA. Scapular arch internal to ribs; temporal region with complex roof and no longitudinal bars. A presternum; limbs ambulatory. Order 2, CHELYDO SAU RIA.