This preliminary list of some of the classes of the algae has been prepared, mainly for the use of British phycologists, to form a basis on which to work for the eventual compilation of a complete check and localitylist of all species of British marine algae. The compiler would be grateful for all additions and corrections to this list, and for records of marine species from the algal classes not included in the present list.The classes of algae treated in this list are the Chlorophyceae (S3 gen., IS6 spp.), Xanthophyceae (7 gen., IS spp.), Chrysophyceae(IS gen., 22 spp.), Phaeophyceae (96 gen., 199 spp.), Rhodophyc;eae(126 gen., 324 spp.), and Cyanophyceae(39 gen., 12Sspp.). The genera are listed alphabeticallyunder the family and the species alphabetically under the genus. If a name has been changed from that given in Newton (1931), the name in Newton is added, in brackets, below. Names preceded by a question mark appear to need revision for nomenclatural or taxonomic reasons. Most of the so-called varieties listed are very probably merely habitat forms of the species, but further investigation is needed before new combinations are made for them. Notes are given at the end of each class, the number in brackets following a name in the list refers to these notes..

The production, longevity, growth, regeneration and reproduction of Laminaria saccharina (L.) Lamour. on the Devon and Argyll coasts are described.Bathymetric zone and habitat control the fertility and longevity of the gametophyte and consequently the production of the sporophyte. Sporophytes develop at the higher levels during the winter, early spring, late summer and autumn, and at the lower levels during spring, summer and autumn.Longevity of the sporophyte depends on season of germination, bathymetric zone and habitat. Winter sporophytes rarely persist to maturity. Spring sporophytes form the bulk of all L. saccharina populations except on very sheltered coasts in the sublittoral zone where summer sporophytes may be equally numerous. On the British coast the life-span of a L. saccharina sporophyte does not exceed 3 years.

The Preliminary Check-list of British Marine Algae (Parke, 1953), with three subsequent lists of additions and corrections (Parke, 1956,1957,1959), was superseded by the Revised Check-list of British Marine Algae (Parke & Dixon, 1964) and the Check-list of British Marine Algae - Second Revision (Parke & Dixon, 1968). Since the publication of the 1968 list, changes, both taxonomic and systematic, have been sufficiently numerous to warrant the present list incorporating further additions, corrections and emendations.

The Preliminary Check-list (Parke, 1953), with the three subsequent lists of additions and corrections (Parke, 1956, 1957, 1959) was intended to provide a fundamental basis for the preparation of a Flora of the British marine algae sponsored by the British Phycological Society. Changes, both taxonomic and systematic, have been so numerous in recent years that a new Check-list is now necessary for the six Classes dealt with in 1953. Five additional Classes, marked below with an asterisk, are also included in the new list. As there is still controversy regarding the status and arrangement of the major algal groups they are here given, as in Parke (1953), the rank of Class.