"Translucent yellowish-white jellyfish with brown markings around the fringe and on the top of the bell. Those atop the bell resemble a compass, with V shapes radiating out from a central point."
"Common off Southern and Western coasts of Britain in summer months."
It's definitely a compass jellyfish, loads of them around the west of Ireland coast. Saw one swim past me when I was at the beach last week. It was worrying but apparently their sting is quite mild. Not sure on what scale tho!