It is shown that the genus Chiasmolithus as currently understood comprises two discrete lineages. It is proposed that these should be formally recognised as separate genera. A new genus, Sullivania, is described and ten new combinations: S. californica, S. consueta, S. danica, S. edwardsii, S. gigas, S. inconspicua, S. minima, S. nitida, S. titus and Cruciplacolithus oulchyensis are introduced. The speculative evolution in the genera Cruciplacolithus, Sullivania and Chiasmolithus is discussed and illustrated.
- Received March 1, 1991.
- Revision received June 1, 1992.
- © 1992 The Micropalaeontological Society