An exceptionally well-preserved early Oligocene diatom assemblage is documented and illustrated from the internal sediment of a gastropod shell, which was collected from glacial sedments recovered at ODP Site 739, Prydz Bay, Antarctica. The diatoms were deposited between 35.9 and 34.8 Ma according to diatom and calcareous nannofossil stratigraphy, apparently soon after a period of major ice sheet advance across the Prydz Bay continental shelf. The diatom assemblage is neritic in character, but it can readily be correlated with open ocean assemblages from the Southern Ocean as well as with similar material recovered from the CIROS-1 drillhole in the Ross Sea. -Authors