A hydromedusa from the Antarctic, R. lizzioides sp. nov. is described and illustrated. The species is characterizedby its rounded bell-shaped form, being almost as broad as high, the presence of an apical dome and a gastric peduncle, the 4 unbranched oral arms, the number of nematocyst clusters (7-18in specimens 1.5 mm or greater in height), the occasional presence of 1 or more nematocyst clusters near the mouth margin, the 5-7 tentacles in each perradial tentacular bulb, the 3-5 tentacles in each interradial tentacular bulb, and the ovoid shape of the tentacular bulb. A key to the known species of Rathkea is provided.figs. 1-2, tabs. 1-2.Descriptor: Rathkea lizzoides
