Intertidal Communities of the Poor Knights Islands, New Zealand. By L. M. Cranwell, M.A., F.L.S., Auckland Museum, and L. B. Moore, M.Sc., Auckland University College. [Read before the Auckland Institute, June 9, 1937; Received by Editor, October 1, 1937; issued separately, March, 1938.] Contents. Introduction. Description of Poor Knights. General Environmental Conditions. The Biotic Communities. The Zonation. Chthamalus Association. Apophlaea-Elminius Association. Novastoa-encrusting coralline Association. Nemastoma Association. Xiphophora Association. D'Urvillea Association. Carpophyllum elongatum Association. Alternatives to C. elongatum. Sublittoral communities. Notes on Special Habitats. Discussion and Comparison with Other Areas. Introduction. One of the most striking features of certain of the off-shore islands of the North Auckland coast is the many-ranked and beautifully symmetrical zonation of intertidal communities. Bands of sessile shellfish and seaweeds run like white, red, and brown ribbons around the shores, a striking local expression of the incidence of certain major factors operating throughout the whole littoral region. An evaluation of these factors has nowhere been completed satisfactorily, and little attention has been paid them in New Zealand. After a period of observing and collecting on the mainland and various islands from East Cape northwards almost to Cape Brett we chose the Poor Knights Group, which illustrates an extreme of exposure for this coast, for an analysis of the biotic communities, in the hope that there, under exceptionally uniform conditions, controlling factors might be more easily recognisable. Published work on the ecology of the group has been restricted to descriptions of the remarkable land vegetation by Cockayne (1906), Oliver (1925), and Cranwell (1937), and of the breeding habits of certain seabirds by Falla (1934). Notes on birds have also been given by H. Hamilton (1925) and there are odd references to the vegetation in our paper on the Hen and Chickens Islands (1935). It is hoped that the present account may suffice for comparison with other parts of the New Zealand coasts, although with the time available,