Early Ordovician (Arenig) paleogeography, major rock suites and potential ocean surface currents; based on remanent magnetism data supplemented by plots of the positions of shelf sea carbonates and reefs.
European lancelet (Branchiostoma lanceolatum). (After J. E. Webb, On the populations of Branchiostoma lanceolatum and their relations with the West African lancelets, Proc. Zool. Soc. Lond., 127:131, 1956)