ABSTRACT
The Dinoflagellata, as a group, are prominently represented in the marine plankton, being second only to the diatoms in their abundance, and in their importance as a source of food for other planktonic forms and some fishes. In addition to the truly planktonic genera, of which Ceratium and Peridinium are the most abundant in British waters, a number of shore-living forms, occurring between the sand-grains in the tidal area, are frequently present in such profusion as to cause discoloration of the sand-surface. These latter, comprised chiefly in the genera Amphidinium and Gymnodinium, have received much attention within recent years, and the series of reports by W. A. Herdman (1911-14), Laurie (1914), and E. C. Herdman (1921-24) upon their occurrence, habits, and morphology, have thrown much light upon a hitherto obscure and neglected group, and have served to emphasise the profound importance of the rôle played by these minute organisms in the biological complex of the sandy beach.
