1. Brahic, A.: 1977, Astron. Astrophys. 54, 895.
2. Clairemidi, S.: 1982, in A. Brahic (ed.), ?Planetary Rings?, IAU Colloq. 75, 397.
3. Clairemidi, S.: 1987a, Earth, Moon and Planets 38, 237.
4. Clairemidi, S.: 1987b, Earth, Moon and Planets 39, 21 (this issue).
5. Clairemidi, S. and Brahic, A.: 1986, submitted to Icarus.