Taxonomic review of the acritarch genera Acanthodiacrodium Timofeev, 1958 and Diornatosphaera downie, 1958

Following a previous suggestion, the acritarch genus Acanthodiacrodium Timofeev, 1958 is restricted to its type species A. dentiferum Timofeev, 1958; also, an emendation of the genus Diornatosphaera Downie, 1958 is proposed. About 152 species of Acanthodiacrodium are validity published; four of them are formally transferred herein to Diornatosphaera; viz., D. angusta (Downie, 1958), the type species; D. comptula (Rasul, 1979); D. echinata (Timofeev, 1959) and D. golubii (Fensome et al., 1990).