1. Bania, T.M., and Lockman, F.J. 1982 (submitted for publication).
2. Brahic, A. 1977, Astr. Ap., 54, 895.
3. Chevalier, R.A. 1977, Ann. Rev. Astr. Ap., 15, 175.
4. Comins, N. 1981, M.N.R.A.S., 194, 169.
5. Cox, D.P., and Smith, B.W. 1974, Ap. J. (Letters), 189, L105.