Early Australian volutiform gastropods (Caenogastropoda: Neogastropoda) from the Cretaceous and Palaeocene: description of Eovolutilithes miria n. sp. and Costopeplum n. gen.

Australia supports a highly distinctive volute fauna, yet the early history of the group is obscured by a fragmented fossil record. Here, we re-examine two early Australian volutiform representatives: the first, from Maastrichtian deposits of the Miria Formation (Carnarvon Basin, Western Australia) and previously referred to Eovolutilithes cf. subsemiplicatus (d'Orbigny, 1850), represents an undescribed member of the extinct Pholidotomidae (Neogastropoda: Pholidotomoidea), which we name Eovolutilithes miria n. sp. The second, Mitra? rhytidata Darragh, 1997 (Mitridae) from the Palaeocene Pebble Point Formation (Otway Basin, Victoria), is reassigned to the Volutidae based on the re-evaluation of its overall morphology, teleoconch sculpture and columellar plait characters. Due to its multispiral protoconch, which distinguishes it from the morphologically similar volute Notopeplum H. J. Finlay, 1927, we erect Costopeplum n. gen. and introduce Costopeplum rhytidatum n. gen. & n. comb. The appearance of C. rhytidatum within a cosmopolitan Palaeocene assemblage is consistent with planktotrophic dispersal, whereas Eocene Australian volutes indicate later transitions toward non-planktotrophy.