Following a restudy of the type material of Muderongia simplexAlberti 1961, this species and the informally-named Volgian morphotype Muderongia sp. A of Davey (1979) are deemed to be unequivocally conspecific. They both have angular endocysts, the extremities of which extend into the pericystal horns, thereby engendering a cornucavate cyst organisation. The specific diagnosis of Muderongia simplex is emended to note this morphologic phenomenon. The distinctive Lower Cretaceous (Ryazanian to Hauterivian–Barremian) circumcavate representatives of Muderongia which have been extensively referred to as Muderongia simplex in the literature are assigned to the new species Muderongia endovata. The distinction between the genera Muderongia and Phoberocysta is maintained, contrary to a recent synonymisation.