A Haplotaeniatum-dominated radiolarian fauna has been discovered in Llandoverian (Early Silurian) strata of the Scandinavian platform, Dalarna, Sweden. As one of six occurrences of this fauna world-wide, it supports the premise that many elements in the Haplotaeniatum Assemblage have a wide geographic distribution and will be of significance in building an Early Silurian radiolarian biostratigraphic scheme with global application. In addition to Haplotaeniatum, this fauna contains palaeoscenidiid and secuicollactine taxa that are known only from one other locality, the Cape Phillips Formation, Canadian Arctic. These taxa may prove to be fairly cosmopolitan and biostratigraphically useful as more data from other localities are collected. Two new genera, Labyrinthosphaera and Gyrosphaera, and three new species, Labyrinthosphaera macdonaldi, Gyrosphaera siljanensis, and Gyrosphaera raneatela, are described herein. Labyrinthosphaera has a multi-layered labyrinthine meshwork and with six or more tri-bladed spines. Gyrosphaera has a labyrinthine meshwork and displays spiraliform layering, similar to that described in Haplotaeniatum, indicating a close phylogenetic link between these two Llandoverian taxa. Further data from additional localities is needed to determine the potential diachroneity of a global Haplotaeniatum acme zone, and to identify additional taxa whose first and last occurrences may be used as biostratigraphic datums for the Llandoverian.

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