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 tarphyceratid 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 regarding 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.

Key words: Tarphyceratida, Trocholites ,micro CT, Darriwilian, Sandbian/Katian, Prague Basin, Baltica, peri-Gondwana, Bohemia.

Martina Aubrechtová [aubrechm@gmail.com; ORCID: https://orcid.org/0000-0002-9804-3249], Institute of Geology, Czech Academy of Sciences, Rozvojová 269, 16500 Prague 6, Czech Republic; Institute of Geology and Palaeontology, Faculty of Science, Charles University in Prague, Albertov 6, 12843 Prague 2, Czech Republic. Vojtěch Turek [vojtech_turek@nm.cz; ORCID: https://orcid.org/0000-0001-7366-8229], National Museum Prague, Václavské náměstí 68, 115 79 Prague 1, Czech Republic. Štěpán Manda [stepan.manda@geology.cz; ORCID: https://orcid.org/0000-0002-4939-2063], Czech Geological Survey, Klárov 3, 11821 Prague 1, Czech Republic.