Potoxylon melagangai is a common tree growing on the river floodplain of the Melinau River at Mulu Park HQ. where these seeds were photographed.
There are two trees called Belian in Borneo, Potoxylon melagangai and Eusideroxylon zwageri. We were unable to locate any Eusideroxylon zwageri at Mulu.
According to James LaFrankie (2010) Eusideroxylon zwageri does not grow north of Sibu in Sarawak on the west coast of Borneo.