Late Ordovician Bivalvia Heteroconchia (Cycloconchidae and Glyptarcidae) from western Argentina

On the basis of existing and new collections from northwestern Argentina (Sierra de Zapla and Sierra de Mojotoro) as well as from the Precordillera (San Juan Province), two new genera of the Superorder Heteroconchia Hertwig are erected. Specimens from the Santa Gertrudis Formation (Late Llanvirn-Early Caradoc, Quebrada del Gallinato, Sierra de Mojotoro) assigned to Cycloconcha cf. C. oblonga Foerste were revised, and on the basis of new collections from the Capillas Formation (Sierra de Zapla) a new taxon of Glyptarcidae Cope, Zaplaella capillaensis gen. and sp. nov., is erected. Poladonta sanjuanina gen. and sp. nov. is proposed for unnamed, previously studied specimens of Cycloconchidae Ulrich from Early Caradoc pebbles contained in the basal diamictite of the Don Braulio Formation (Precordillera basin).