The Genus Codium in New Zealand Part I. Systematics* This investigation was carried out during the tenure of a University of New Zealand Research Fund Fellowship at Auckland University College. Vivienne Dellow, Department of Botany Victoria University College, Wellington [Read before the Wellington Branch, August 28, 1951; received by the Editor, August 28, 1951] Summary The genus Codium is represented in New Zealand waters by six species. The New Zealand members of Codium adhaerens. (Cabr.) Ag. have been split up into a northern and a southern variety, var. convolutum var. nov., type locality Motutapu, and var. incrassatum var. nov., type locality Stewart Island. The differences from C. adhaerens (s.str.) are not regarded as of sufficient magnitude to warrant the creation of new species. Gametangia are figured for the first time in Codium cranwelliae. C. mamillosum Harv. and C. muelleri Kuetz do not occur in New Zealand. Owing chiefly to the larger size of the utricles, the New Zealand members of C. dichotomum have been assigned to a new form, f. novo-zelandicum, type locality Lyttelton. In spite of great variation in utricle size and shape among individuals belonging to the Codium fragile assemblage, there are no constant differences on which to base the formation of new varieties. C. fragile var. gracile O. C. Schmidt has been raised to the rank of a separate species, under the new combination Codium gracile. No intermediate forms have been found which might be a connecting link between C. fragile and C. gracile. Codium cuneatum in New Zealand has typically thick, striated utricle apices, and has been described accordingly as f. striatissimum f. nov., type locality Bay of Islands. Introduction An investigation of herbarium and preserved material of both overseas and New Zealand specimens has shown that six species of Codium inhabit New Zealand waters. Dried material has been examined from the herbaria of the late R. M. Laing, the Botany Division of the Department of Scientific and Industrial Research, Professor V. J. Chapman, Mr. V. W. Lindauer, and from the writer's own herbarium. Preserved specimens have been collected mainly by the writer, excluding those from the Southern Fiords, Stewart Island, and the Subantarctic Islands. Wherever possible, descriptions are based on material preserved in 5 per cent. formalin in seawater, since dried specimens are extremely unreliable as a basis for accurate measurements. Tissues removed from herbarium sheets were swollen as nearly as possible to normal size by boiling or placing for 24 hours in a solution of the detergent Ados No. 3. Classification Setchell (in Lucas, 1935) proposed a division of Codium into 2 sub-genera: (a) Tylecodium—cushion-like forms with typically branched utricles; (b) Schizocodium—dichotomous forms, with utricles mainly simple. Schmidt, following De Toni, earlier recognised 4 sections, each of which he divided into 2 subsections. The most primitive group is regarded by him as that of the Adhaerentia, members of which are more or less flattened and crustose or sponge-like, with a surface region of palisade utricles and a subsurface region of medullary filaments. Attachment is effected by means of rhizoids over the entire lower surface. Slightly more advanced in complexity is the Bursae group,