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. Species of Aulacodiscus and Trinacria, two important marinediatom genera with biostratigraphic utility in offshore North Sea explorationand onshore correlation, are identified, described andemended and the North Sea microfaunal zonation scheme is revised accordingly. Occurring mainly aspyritised diatom moulds or steinkerns, detailed scanning electron microscope(SEM) analysis of several specimens, formerly in open nomenclature, hasallowed the correct taxonomic identification of pyritised morphologies foundto belong to the genus Aulacodiscus, including A. allorgei,A. heterostictus, A. insignis, A. singilewskyanus, A. subexcavatus and A. suspectus. Theimportant marker species Trinacria regina is emended. SEM studies,using specimens preserved in pyrite and original silica, have shed furtherlight on the varying forms and frustule morphology of Trinacria regina so that valves and frustules formerly thought to represent separatespecies are now found to be grouped within this taxon; SEM studies have shownthat many of these variations represent different valves within a chain,whilst others may signify ecophenotypic variants. Emendments are thereforemade to clarify the taxonomic status of different variants withinT. regina, important inthe Palaeocene–Eocene boundary interval onshore and offshore such as theSele and Balder formations and the Fur Formation diatomite of Jutland,Denmark. Species of taxa formerly in open nomenclature are now assigned toAulacodiscus insignis, which are important offshore markers inoffshore late Oligocene to early Miocene sediments in northwest Europe.

journal of micropalaeontology

Species of the diatom taxa &amp;lt;i&amp;gt;Aulacodiscus&amp;lt;/i&amp;gt; and &amp;lt;i&amp;gt;Trinacria&amp;lt;/i&amp;gt; with biostratigraphic utility in Palaeogene and Neogene North Sea sediments