on the basis of collections from tremadoc and arenig successions of northwestern argentina, the affinities of goniophorina isberg, 1934, are reassessed. studied material includes ucumariids, lipanellids, goniophorina , and other specimens for which the new genus lossella is proposed with the new species l . juancruzi sp. nov. as type species. goniophorina and lossella are grouped in the new family goniophorinidae. synapomorphies of goniophorinids, ucumariids, and lipanellids lead to the conclusion that goniophorina integrates a major group of edentulous bivalves, a lineage of which -the ucumariidsprobably gave rise to anomalodesmata. this fauna represents a rapid, local diversification event that is part of the west-gondwanan bivalve radiation during the early ordovician.