Specimens of Myophorianeuquensis, type species of Groeberella Leanza, collected from new Sinemunian-Pliensbachian localities of Chile and Argentina, have increased the knowledge of its diagnostic characters; these are here presented in a complementary description of the species and in an emended genus diagnosis. Groeberella is known in the Lower Jurassic of Chile (G. neuquensis and G. sp.) and Argentina (G. neuquensis) and in the Middle Jurassic of Argentina (G. sp, indet. Leanza). The new localities recorded in Argentina and Chile, between latitudes 26 degrees 02' and 44 degrees 30'S, extend the known geographical distribution. Groeberella increases the number of bivalve genera of chronostratigraphical importance in the Jurassic of South America. Due to the fact that the morphological characters of Groeberella are not present in any of the families with trigonian hinge of the order Trigonioida, Groeberellidae nov., is proposed herein. This taxon is characterized by forms with external myophorian shape, trigonian dentition, plain area and escutcheon, prominent carinae, and flank with radial costae. Also described is Groeberella so., based on scarce and moderately well preserved specimens, collected from sinemurian strata of Quebrada Pan de Azucar, Northern Chile.