Three species of Porambonitids are described from the Middle Ordovician of the Oslo Region, ).[orway. One of them, Porambonites (Porambonites) kjerulfi is new. The nomenclature, taxonomy and evolution of the farnily are discussed. The new species (P. (P.) kjerulfi) is related to the Lower Ordovician representatives of the farnily, and similar species are also found in other parts of Western Europe during the Middle Ordovician. The two other species, which both belong to the subgenus Isorhynchus KING, are Baltic ones.