The endemic Patagonian genus Titomaya gen. nov. is erected to include the Danian Meretrix chalcedonica (Lefipan and Salamanca formations) and Titomaya longobucca sp. nov. (Salamanca Formation) from the Chubut Province (Argentina). Although Meretrix and Titomaya share the same characteristic sculpture of their nymphs, Titomaya is differentiated by having medium to small, subtriangular, higher than long shells, a narrower and shorter hinge plate, smaller cardinal and anterior teeth, and by the development of a deeper pallial sinus. This new genus rules out the presence of Meretrix in Patagonia, as was long believed, and increases the list of endemic taxa that characterize the Danian assemblages of Patagonia.