SUMMARYA second record of the occurrence ofPorphyridium sordidumGeitler 1932 is reported. Cultures were obtained by plating crude material on agar plates of various salinities with the higher salinities selectively favoring the growth of this species. Proposed synonymy ofP. sordidumwithP. cruentumis rejected. The author suggests that more attention be given to the establishment and use of depositories for living unialgal, reference cultures in taxonomical work on the more delicate algae, and that taxonomical manipulations of such forms based only upon word descriptions and the study of dried herbarium material should be viewed with a degree of caution.