A review of certain non-tabulate Cretaceous hystrichospherid dinocysts

Abstract

Species assignable to three Cretaceous non-tabulate hystrichospherid dinocysts genera, Kleithriasphaeridium, Florentinia and Silicisphaera gen. nov. are reviewed and five new species proposed: K. loffrensis, F. resex, S. buspina, S. tenera and S? torulosa. Members of these genera are basically spherical in shape, possess either a precingular (3″) or combination precingular (3″)-apical archaeopyle and a variable number of differently shaped intratabular processes. Specific differentiation is based mainly on variation in process number and size. Much of the new information given in this paper is derived from the study of material from (1) the Ryazanian and Valanginian of eastern England, and (2) the Late Albian to Senonian of the Loffre Borehole, northern France. The stratigraphic ranges of all the species are discussed; since a succession of stratigraphic appearances and extinctions occurs in the Cretaceous and the ranges of individual species are fairly limited, careful identification of species will give fine stratigraphic control. The new genus, Silicisphaera, first appears in the mid-Turonian and apparently becomes extinct by the close of the Senonian. Florentinia and Silicisphaera are considered to be ancestral to the Tertiary Diphyes and Hystrichokolpoma.