Arthrorhachis Hawle and Corda, 1984 (Agnostida) in the Prague Basin (Barrandian area, Czech Republic) revisited

The agnostid Arthrorhachis Hawle & Corda, 1847 from the Prague Basin (type area of its occurrence, including type species of the genus) is revised. The taxonomic position of all earlier established type specimens is clarified. All available material, including recently collected specimens, is described and discussed. The glabellar impressions are described for the first time on material from the Barrandian area. The stratigraphical distribution of the two established species, A. tarda (Barrande, 1846) and A. pragensis (Pribyl & Vanek, 1968) is evaluated. Although Arthrorhachis belongs to the latest agnostids, its representatives are locally common in the dark coloured siltstones of the Zahorany, Bohdalec and especially Kraluv Dvur formations (upper Sandbian-upper Katian interval). In the Prague Basin, the last specimens of Arthrorhachis seem to persist up to the onset of the Hirnantian glaciation. The classical concept of the so-called "Lejskov facies" characteristic by comparatively abundant agnostids is discussed.