Article: The Scandinavian Middle Ordovician trinucleid trilobites

Thirteen species of trinucleid are described from the lower Llanvirn to lower Caradoc platform successions of Norway and Sweden. Of these, five are established taxa, four are described under open nomenclature, and four are new: Bergamia johanssoni sp. nov., Botrioides impostor sp. nov., B. simplex sp. nov., and B. margo sp. nov. The genus Botrioides is stabilized by choosing a neotype for the type species 'Trinucleus' coscinorinus Angelin and placing it in the synonymy of B. bronnii (Boeck). Two species groups are recognized within Botrioides centred on B. bronnii and B. foveolatus (Angelin). Trinucleids were largely restricted to the western, deepest water, parts of the platform. Although the oldest species, Bergamia johanssoni sp. nov., represents an early Llanvirn immigration of an Anglo-Welsh genus, the Baltic stocks were endemic until the mid-Llandeilo when Botrioides spread into the Gondwanan province and possibly Reedolithus extended into Scoto-Appalachian faunas. Middle and late Caradoc immigrations of Broeggerolithus and Tretaspis into Scandinavia were from the Anglo-Welsh basin and North America respectively.