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A new species of bubble-headed trilobite, Staurocephalus oliveae sp. nov., is described from 250 specimens collected from a recently discovered locality in the Sholeshook Limestone Formation (upper Katian, Upper Ordovician; Ashgill, Cautleyan Zone 1 equivalent) in the village of Llanddowror, Carmarthenshire. Although no fully articulated specimens were found, the material is the most abundant and well-preserved of any Ordovician Staurocephalus species known from Britain and Ireland, and enables the complicated 3D structure of its cephalon to be reconstructed. Staurocephalus oliveae sp. nov. is the earliest representative of the genus recorded in Avalonia, following its presumed migration into the area from Laurentia or Baltica. Recognition of this Cautleyan species resurrects the potential usefulness of the long established, widely distributed, Staurocephalus clavifrons as a latest Katian (= Rawtheyan) indicator. [ABSTRACT FROM AUTHOR]

The taxonomic status of the stratigraphically–important Caradoc genera Salterolithus Bancroft, 1929, Broeggerolithus Lamont, 1935 and Smeathenia Dean, 1960 and the species therein is critically reviewed. The radial alignment patterns of the fringe pits within the E arcs are used to distinguish Salterolithus from Broeggerolithus; fringe morphology and pit counts are used to distinguish species within these genera. ‘Broeggerolithus’ harnagensis is reassigned to Salterolithus and S. praecursor, S. caractaci paucus and Smeathenia smeathenensis are all regarded as junior synonyms of Salterolithus harnagensis. This revision of the Anglo–Welsh Cryptolithinae reveals the evolution of morphologically very variable populations and environmentally constrained morphotypes and species. Eight species and subspecies of Salterolithus and Broeggerolithus are retained and redescribed and their stratigraphical distribution in the Caradoc of Britain, Ireland, Belgium and Scandinavia is clarified. [ABSTRACT FROM AUTHOR]