Micrhystridium pumile (O. Wetzel, 1932 ex 0. Wetzel, 1933) Downie and Sarjeant, 1965

Name illegitimate; nomenclatural jr. synonym of the acritarch taxon Hystrichosphaera (now Baltisphaeridium) longispinosa forma longispinosa, the potential autonym since, in validating Hystrichosphaera longispinosa forma pumilis, O. Wetzel, 1933 included in synonymy the holotype of the species. See also Hystrichosphaera longispinosa forma pumilis (name illegitimate),
Hystrichosphaeridium pumile (name illegitimate), Diacrocanthidium? pumile (name illegitimate) and Baltisphaeridium pumile (an acritarch species; combination not validly published). Deflandre, 1937 proposed the elevation of this taxon to specific rank as Hystrichosphaeridium pumile. The name Hystrichosphaera longispinosa forma pumilis, although accompanied by a description, was not validly published by O. Wetzel, 1932 since the generic name Hystrichosphaera was not validated
until 1933.
Holotype: O. Wetzel, 1933, pl.4, fig.24; designated by Sarjeant, 1985
Age: Late Cretaceous (based on material from an erratic)