Abstract: After the first dinoflagellates monograph was published in China in 1978, the new information about the Bobaidinioid group has been accumulated, which results in reviewing our understanding of this group. The main emendations here emphasize the combination archeopyle of tAa+3Ia or tAa+3I type, the number and distribution of girdle projections, and the nature of girdle folds of this group, on which the systematic position of Bohaidinioideae belonging to Deflandreaceae of Peridiniineae has been allocated. Five forms of seven species of four genera have been emended, and two new species and three new forms have also been described in this paper. They are Bohaidina alveolae, B. spinosa form spinosa, B. spinosa form quadrata, and B. spinosa form fusiforma. In addition an attemp has been made of reconstructing the paleoecology of Bohaidinioideae and its possible role in the process of dinoflagellates migration from marine to freshwater, based on reviewing the geological history of nonmarine dinoflagellate records in the world, the occurrence of Bohaidinioideae and other associated genera and species in the same stratum, combined with available geological and palaeontological evidences.

Key words: Bohaidinioid dinoflagellates, Combination archeopyle, Girle proiection and girdle filds