The Carnian-Rhaetian genus Miliolipora (Soritoidea, Milioliporidae) is characterised by a coarsely perforated porcelaneous wall and a quinqueloculinoid arrangement of semi-tubular chambers. Miliolipora tamarae nov. sp. has been documented in the Rhaetian Dachstein reef limestone of Mt. Begunjˇsˇcica (Karavanke Mts., northern Slovenia). This new species differs from Miliolipora cuvillieri Brönnimann and Zaninetti in its costate outer chambers and evolute coiling. Both species are abundant in an oncoid rudstone/grapestone facies located immediately behind the central reef zone. In this depositional context, Miliolipora spp. were subjected to mechanical sorting and are believed to have been transported a short distance from their habitat. The costae and the overall less rounded shape of the test helped to stabilize M. tamarae nov. sp. on the sea floor. Both species were widely spread in the Tethyan realm confirming the broad palaeobiogeographic distribution of the Late Triassic foraminifera.