1. Cloud, jun., P. E., in Evolution and Environment (edit. by Drake, E. T.), 1 (Yale Univ. Press, New Haven, 1968).
2. Glaessner, M. F., Biol. Rev., 37, 467 (1962).
3. Glaessner, M. F., and Wade, M., Paleontology, 9, 599 (1966).
4. Berkner, L. V., and Marshall, L. C., Proc. US Nat. Acad. Sci., 53, 1215 (1965).
5. Cloud, jun., P. E., Science, 148, 27 (1965).