After the circulation of the preliminary version of this work (January 1961) the author has learned of a similar theory put forward independently and simultaneously by Y. Ne'eman (Nuclear Physics, to be published). Earlier uses of the 3 dimensional unitary group in connection with the Sakata model are reported by Y. Ohnuki at the 1960 Rochester Conference on High Energy Physics. A. Salam and J. Ward (Nuovo Cimento, to be published) have considered related questions. The author would like to thank Dr. Ne'eman and Professor Salam for communicating their results to him.