The continuous sequence of Maastrichtian to Paleocene sediments exposed in the Sierra Dorotea area in southwestern Santa Cruz (Argentina) contains a rich molluscan fauna with many elements characteristic of the Weddellian Faunistic Province. The presence in this fauna of genera such as Taioma, Heteroterma, Fyfea, Zemacies, and Priscaphander suggests close affinities with faunas of similar age from New Zealand, further supporting the existence of continuous shallow-sea conditions along the southern margin of the Pacific Ocean during the end of the Cretaceous and beginning of the Tertiary. In this paper 25 species are described, of which six are new: Pseudofax costellatus n. sp., Taioma patagonica n. sp., Heteroterma elegans n. sp., Fyfea beui n. sp., Priscaphander sanjosensis n. sp., and Priscaphander bracaccinii n. sp.