A reappraisal of the lower Silurian brachiopods Borealis and Pentamerus

The pentamerids Borealis borealis and Pentamerus oblongus are redescribed and a new subspecies B. borealis osloensis subsp. nov. is erected. Specimens from the virtually continuous Llandovery succession of the Oslo Region show a gradational evolution from B. borealis to P. oblongus, with a transition within the Idwian The occurrence of different evolutionary forms suggests a diachronous base for the limestone unit containin; these fossils in the Oslo Region. The recognition of this phyletic lineage may further improve the correlation to lower Silurian shelly faunas of the Oslo Region, Estonia, and Great Britai