This paper deals with the occurrence pattern of the ephyra stage of the jelly-fish, Aurelia aurita LAMARCK, in Urazoko Bay near Tsuruga. Sampling of the material and hydrographic observations were made usually twice a month by vertical haul of a plankton-net (45cm in mouth aperture, 0.33mm in mesh) throughout the period from November 1966 to October 1967. The results obtained are summarized as follows:
1) The ephyrae occurred from middle January to late June, with the peak in April. Therefore, storobilation of the polyp of Aurelia aurita was supposed to continue through the early season of the above-mentioned period in this bay.
2) Ephyrae were distributed rather evenly in the inner part as well as in the mouth of the bay, except when the highest population density showed 33.1-68.0 per m³ in the inner part of the bay in April.
3) Ephyrae occurred at 8°-22°C in surface water temperature, 15.9-18.9‰ in surface chlorinity; they were observed to occur 10.1 per m³ in population density in water at 11°-21°C, in temperature and 16.9-18.8‰ in chlorinity.