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The first six of the eight DSDP Leg 21 sites yielded silicoflagellates in some intervals. Site data including the age of assemblages recorded in each of them are as follows: Site 203: 22°09.22'S, 177°32.77'W;water depth 2720 meters; Quaternary. Site 204: 24°57.27'S, 174°06.69'W; water depth 5354 meters; Recent with Maastrichtian reworking. Site 205: 25°30.99'S, 177°53.95'E; water depth 4320 meters;late Miocene. Site 206 (with holes 206 and 206C): 32°00.75'S, 165°27.15'E; water depth 3196 meters; middle Eocene, late Oligocene, Miocene, Pliocene, Quaternary. Hole 207A: 36°57.75'S, 165°26.06'E; water depth 1389 meters;middle Eocene. Site 208: 26°06.6l'S, 161°13.27'E; water depth 1545 meters; early Paleocene. The late Oligocene to Quaternary silicoflagellates from Sites 203 through 206 and some species from the early Paleocene at Site 208 have been particularly investigated for this report. In addition, a few incertae sedis microfossils are included for their biostratigraphic value. No information is given on the middle Eocene silicoflagellates. Most data discussed herein came from the investigations of core catcher samples prepared aboard the drilling vessel. Although the distance between such samples is about 9 meters, they gave sufficiently detailed information about the range of the taxa concerned in the thick late Oligocene-Pleistocene sequence. Since this sequence is almost continuously cored and yields fairly rich assemblages, the main purposes of this report are the biostratigraphic zonation of this interval and improvement of the zonation established by Martini (1971) for the equatorial Pacific sediments cored in Leg 7 of the DSDP. For these purposes, in addition to the Leg 21 core catcher samples, some from Site 66.1 (western Equatorial Pacific) and Site 33 (northeastern Pacific), kindly provided for radiolarian studies by the DSDP Sample Distribution Panel, have been investigated as well (Figures 1, 2, and 3). The species determined previously from these two sites are not always similar to those determined by us, and for a better correlation, it was necessary that they should have the same content. Particular attention was paid to some systematic questions since the successful use of the silicoflagellates in biostratigraphy depends in a great measure on the accurate determination of the taxa. Many of the opinions regarding these questions expressed herein are different from those of previous authors. This reflects the stage of present-day knowledge of the silicoflagellates, whereby the morphologic systematics is controlled by the temporal and spatial distribution of the taxa and is influenced by our Phylogenetic constructions. In order to support some opinions, we made use of statistical data and of supplementary information obtained from the study of other silicoflagellate assemblages. Of course, some of the taxa used and some of the Phylogenetic linneages proposed are controversial. Such controversies are inherent in any group, the systematics of which is in a state of flux. This is especially true of the silicoflagellates, where the wide variability sometimes raises very difficult problems.

Paleocene, Late Oligocene and Post-Oligocene Silicoflagellates in Southwestern Pacific Sediments Cored on DSDP Leg 21