A new rare Upper Ordovician mound dwelling palaeoloricate chiton is described as <i>Crassaplax collicola</i> gen. et sp. nov. from three large isolated intermediate valves from the Katian carbonate mud mounds of the Boda Limestone in the Siljan district of central Sweden. Together with the previously known <i>Spicuchelodes</i>? sp., also from the Boda Limestone, these are the only known Late Ordovician ...