From culture studies it appears that the species of Erythrocladia and Erythrotrichia have a great morphological variability. The delimitation of the species has been studied. In the genus Erythrocladia two species are recognized, in Erythrotrichia three, and in Porphyropsis two. In cultures of Erythrotrichia carnea a conchocelis stage was found; its morphological structure is similar to that of the conchocelis thalli as described for Bangia and Porphyra. The mode of spore formation in the conchocelis thalli is, however, different; in Erythrotrichia monospores were formed whereas in Bangia and Porphyra only neutral spores are known. Cell-fusions were observed in filaments of Erythrotrichia carnea; this could indicate the occurrence of sexual reproduction. There is a striking agreement with the observations made bij Flint and Magne on Kyliniella and Rhodochaete respectively. Besides a preliminary scheme of the life-cycle of Erythrotrichia carnea, information on distribution, cytology, development, and asexual reproduction of all species is given.