Gephyrostegus bohemicus Jaekel from the Upper Carboniferous of Nyran is the oldest and most primitive member of the Seymouriamorpha. A new description is given based partly on the described material, but mainly on two hitherto undescribed specimens. These specimens are remarkably complete and make possible a description of the palate, previously unknown, and also a comparative study of the development of the vertebrae. The single specimen, also from Nyran, described by Watson (1926) as Diplovertebron punctatum is made the type of a new species G. watsoni. The position of Gephyrostegus in the Seymouriamorpha is discussed. Its primitive nature is emphasized and a comparison is made with later more specialized forms. The relationship of early tetrapods is considered and a new classification suggested.