This thesis proposes to deal with certain species or the genus Cystophora, a fucoid common on many rocky coasts of Australasia. Three species (C. retroflexa, C. scalaris, C. torulosa) were collected from Lyttelton Harbour, South Island, New Zealand, (Map, Figs. 1,2.) and are discussed in some detail; they were identified with certainty only late in the year, after an extensive examination of all the available literature (which was far from complete), and of some herbarium specimens (for the most part doubtfully identified or not at all). The results however have furnished an account of all the known New Zealand species; this account, though in the main a compilation and comparison of earlier writers, is based on the very reliable works of J. Agardh and so can lay claim to accuracy. The anatomy and oecology, and in the main the general morphology, research methods, and some other parts, are based on actual work on the collected specimens of the above three species. Earlier work has been entirely descriptive of the morphology.