1. Fraser, F. C. & Purves, P. E. Proc. R. Soc. Lond. 152, 62–78 (1960).
2. Purves, P. E. in Whales, Dolphins, and Porposes (ed. Norris, K. S.) 320–378 (Univ. California Press, Berkeley, 1966).
3. Reysenbach de Haan, F. W. Acta otolar. Suppl. 134, 1 (1957).
4. Fleischer, G. Adv. Anat. embryol. Cell Biol. 55, 1–70 (1978).
5. Gingerich, P. D. & Russell, D. E. Contr. Mus. Paleont. Univ. Mich. 25, 235–246 (1981).