1. 1. Hughes, C. P. Bull. Br. Mus. Nat. Hist. (Geol.) 18, 39–103 (1969). 2. Hughes, C. P. Bull. Br. Mus. Nat. Hist. (Geol.) 20, 115–182 (1971). 3. Hughes, C. P. Bull. Br. Mus. Nat. Hist. (Geol.) 32, 109–81 (1979). 4. Sheldon, P. R. thesis, Univ. Cambridge (1987). 5. Sheldon, P. R. Lethaia (in the press). 6. McNamara, K. J. J. Paleont. 60, 4–13 (1986). 7. Stanley, S. M. Macroevolution, pattern and process (Freeman, San Francisco, 1979). 8. Fortey, R. A. Spec. Pap. Palaeont. 33, 17–28 (1985). 9. Charlesworth, B. Paleobiology 10, 319–327 (1984). 10. Malmgren, B. A. & Kennett, J. P. Paleobiology 7, 230–240 (1981).