The fossils from Muara Kobun were collected by M. Schmidt (Royal Dutch Petroleum Company) as far back as 1902. Eighteen species, including two new ones (Cerithium (Gourmya) kobunense and Carditella witkampi) have been examined, the majority being gastropods whose combined stratigraphical ranges suggest a Preangerian age, with, however, the additional stipulation that perhaps some level high up in Tertiary f3 is involved rather than an age comparable to that of the Gelingseh faunas first partly described by K. Martin and the present writer. The molluscs from Pulu Senumpah were collected by L.M.R. Rutten in the period 1911-1913. There are no more than seven species, all gastropods, over half of which indicate best relationships with the Muara Kobun fauna, hence their being tentatively assigned the same age.