Modiomytilus, a new mytilid bivalve from the Tertiary of southern Patagonia

Abstract

Modiomytilus n. gen. is described from Tertiary sediments exposed in the southwestern corner of Santa Cruz province (Argentina). This large mytilid is characterized by its ornamentation of strong comarginal undulations, its smooth ligamentary ridge, and its relatively large anterior adductor muscle. Two new species are assigned to it: Modiomytilus argentinensis n. sp., from the Centinela Formation (Miocene) south of Lago Argentino, and Modiomytilus mercerati n. sp., from the Río Turbio Formation (Eocene) in Sierra Dorotea. Although other species belonging to this new taxon and previously referred to Mytilus have been described from Tertiary sediments in the region, none are known so far from rocks of comparable age outside Patagonia.