The article offers information on marine phytoplankton of the Welsh coasts, particularly the vicinity of Aberystwyth in Wales. It states that the research done consisted primarily of a detailed investigation into the nature of the phytoplankton of the location, with special attention to temporal and spatial variations. In this research, "regular" sampling nets were towed along a given route for 15 minutes from a small rowing boat. Samples were also obtained from Red Wharf Bay, Moelfe, Bangor, Saundersfoot, and Port Erin, Isle of Man. Accompanying diagrams which illustrate the movement of water in Aberystwyth are also presented.