1. Tucker, D. W., Nature, 183, 495 (1959).
2. Schmidt, J., Phil. Trans. R. Soc., B, 211, 179 (1922).
3. Deelder, C. L., Nature, 185, 589 (1960).
4. Sinha, V. R. P., and Jones, J. W., Proc. Third Br. Coarse Fish Conf., 70 (1967).
5. Fine, J. M., Drilhon, A., Ridgway, G. J., Amouch, P., and Boffa, G., C.r. hebd. Séanc. Acad. Sci., Paris, 265, 58 (1967).