A re-examination of the type material of Lithothamnion crispatum Hauck allowed to identify some tetrasporangial empty conceptacles that were overlooked during a previous revision. The macroscopic morphology and plant habit, the microscopic anatomy of the vegetative thallus and the tetrasporangial conceptacles of the type material have been compared with freshly collected Mediterranean plants. The 5-7 rosette cells surrounding each pore of the tetrasporangial conceptacle roof are larger than the normal epithallial cells and the whole structure (pore and rosette cells) lays in a depression below the conceptacle roof surface. The dioecius gametangial plants are described. The comparison of the reproductive anatomy of Lithothamnion superpositum Foslie 1899 and Lithothamnion crispatum Hauck 1878 shows that both species possess tetrasporangial conceptacle roofs that are pitted with depressions as a consequence of disintegration of uppermost cells in filaments surrounding pore canals. The correspondence of vegetative and reproductive characters demonstrates that they are conspecific, and therefore L. superpositum Foslie must be considered a younger heterotypic synonym of L. crispatum Hauck.
