Abstract
Annual population changes of four species of Stauromedusae at Plymouth are described. Three of these, Haliclystus auricula, Lucernariopsis campanulata and L. cruxmelitensis, have one generation in a year; Craterolophus convolvulus has two. The completion of the life-cycle of the four Plymouth species within a year is in agreement with Berril's (1962) studies of three species on the west Atlantic coast and with a reinterpretation of Sars's (1846) observations on Lucernaria quadricomis on the coast of Norway.

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