Since 1953 the Pliocene-Pleistocene boundary in New Zealand has been set at the base of the Nukumaruan (regional) Stage because that coincides with the abrupt first appearance of the subantarctic bivalve Chlamys delicatula (Hutton) in marine sequences of central New Zealand. However, it is now estimated, on the basis of biostratigraphic, magnetostratigraphic, and radiometric data, that the Nukumaruan commenced at about 2.4 Ma and ended about 1.3 Ma and that the Olduvai subchron approximately coincides with the middle of the Nukumaruan. In the stratotype Nukumaruan, and in correlative sections, a marked lithologic change (interpreted as the result of glacio-eustatic regression) following the first appearance of Gephyrocapsa sinuosa Hay and Beaudry may be correlative with the top of the Olduvai and with the Vrica boundary-stratotype.