In 1908 H. Witkamp, then with the Royal Dutch Petroleum Company, collected a number of molluscan fossils at a locality near Sungai Kari Orang, on the north flank of the Kari Orang anticline, the locality subsequently being known simply as Kari Orang. It yielded also a few corals which were described by J. Felix and H. Gerth and dated as just Miocene. In the present paper 27 molluscan species, containing few bivalves are described from Kari Orang, including 5 new ones: Terebralia? orangensis, Erosaria (Erosaria) kutaiana, Hinia (Uzita) kalimantanensis, Mitra (Mitra) ickeae, and Turridrupa? witkampi. No less than 17 out of 21 species used for age determination occur in Preangerian assemblages, equally close relationships existing with the classical Preangerian of Java and the Lower Gelingseh fauna of East Borneo, while the ties with other Bornean molluscan assemblages are weak to non-existent. It is concluded that the age of the Kari Orang fauna is Preangerian, Tf3.