EARLY CARBONIFEROUS BIVALVIA FROM WESTERN ARGENTINA

Lower Carboniferous deposits of western Argentina yield invertebrates and plant remains. In the Tournaisian epoch, a transgression from the 'Pacific' flooded the Rio Blanco Basin, forming a semi-restricted inla nd sea. Marine invertebrates of this age comprise the Malimanian fauna , which is based on the Protocanites-Rossirhynchus Assemblage. Eleven species of Bivalvia are here described; Palaeoneilo subquadratum sp. n ov., Malimania triangularis gen. et sp. nov.. Phestia sp.. Volsellina? sp. Posidoniella malimanensis sp. nov., Leptodesma? sp., Schizodus sp ., Cypricardinia? sp., Edmondia? sp. Sanguinolites punillanus sp. nov. , and Vacunella? sp. nov. They are accompanied by gastropods, trilobit es, conularids and corals. The Malimanian fauna is regarded as a poorl y to moderately varied assemblage that was influenced by some basinal restrictions. It was probably connected to faunas of Chile and Peru, a nd lived during a stage of mild climate before the beginning of the La te Palaeozoic ice age.