North-West European Thecate Hydroids and their Medusae. Part 1. Laodiceidae to Haleciidae - Cornelius, P. F. S. (In: R.S.K. Barnes & J.H. Crothers, eds, Synopses of the British Fauna (New Series). The Linn. Soc. London and Est. Coas. Sci. Ass. - Field Studies Council., 1995)