Maximizing diductor adhension: An unusual cardinal process in Late Ordovician brachiopods from Estonia

Cardinal process is a structure on dorsal valve of brachio− pods serving for separation or attachment of diductor mus− cles. A cardinal process with a peculiar folded myophore is described from Late Ordovician “Orthis ” kukersiana−group brachiopods assigned to the genus Cyrtonotella (order Or− thida). This structure differs from those of other rhyncho− nelliformean brachiopods and can be considered as a sepa− rate type among about twenty varieties of processes de− scribed up to now. Large Late Ordovician orthoidean brachiopods of the “Orthis” kukersiana group of Öpik (1930) were later (Öpik 1934) as− signed to the genus Cyrtonotella Schuchert and Cooper, 1932. These brachiopods are distributed in the East Baltic throug