Revision of Elektoriskos williereae (G. & M. DEFLANDRE) VANGUESTAINE, 1979 and Dilatisphaera williereae (MARTIN) LISTER, 1970, the primary types Of which come from the Brabant Massif in Belgium, underlines the evidence for their stratigraphic value in the Llandovery, lowest Series of the Silurian. Data indicate that in Belgium and Great Britain the species appear, respectively, slightly above the base of the Rhuddanian and in the upper part of the Aeronian. The stratigraphic level at which they appear in eastern North America, although less well documented, is compatible with the above
