The tarphyceratid cephalopod Trocholites in the Middle-Late Ordovician of the Prague Basin – the Baltican element in peri-Gondwana

. The tarphyceratid cephalopod Trocholites in the Middle –Upper Ordo-vician of the Prague Basin—the Baltican element in peri-Gondwana. Acta Palaeontologica Polonica 68 (3): 529–538. The vast majority of cephalopods of the order Tarphyceratida are known from regions that were located at mid-or low palaeolatitudes during the Ordovician (mainly Baltica, Laurentia, and Chinese palaeoblocks). Only a handful of tarphy - ceratid specimens are known from high palaeolatitude regions of peri-Gondwana and Gondwana. Here, we describe the two best-preserved trocholitid cephalopods known to date from the Ordovician of the Prague Basin. The first is from the late Darriwilian/early Sandbian Dobrotivá Formation and is assigned to Trocholites fugax , a species previously recorded from roughly coeval strata of Iberia, France, and Bohemia. The specimen thus strengthens previous hypotheses regard - ing the interchange of non-benthic faunas between Baltica and different regions of peri-Gondwana during the Middle/ Late Ordovician boundary interval. The second specimen, assigned to a new species of Trocholites chaloupkai sp. nov., is from the late Sandbian–early Katian Zahořany Formation and thus represents one of the stratigraphically youngest Trocholites in the Ordovician of peri-Gondwana. Internal structures of the shell of the holotype of the new species were studied using micro-CT tomography. This revealed that T. chaloupkai sp. nov. closely resembles the stratigraphically older (Darriwilian) species Trocholites depressus from Estonia.