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Abstract
Triceratium unguiculatum Greville and T. pulvinar A. Schmidt are two very similar but distinct species occurring in middle Eocene to Oligocene deposits. Their main difference is in the form and the robustness of their rimoportulae. Descriptions of both are given. They differ from T. favus, the type species of the genus, in having only one rimoportula per elevation and in not having a secondary marginal ridge, a new term defined in the discussion, but they should continue to be placed in Triceratium. Biddulphia reticulata Roper is transferred to Triceratium as T. dictyotum Sims & Ross.