~ulifot.nirr Acnci~tny q f . S c i e~r r~s . Golden G n t~ Pork, So11 Frnncisco. Cnljfornin, 941 18-9961 U.S.A. 2 U.S. Genlng icnl S I O T P~ MS Y 15, Menlo Pork. Cnlvbnt irr. 94025 U.S.A. ABSTRACT: Vcry wcll-prcscrvcd Pliocene diato~ns frorn a diaromi~e u n i~ interbedded within glacial sediments at Ocean Drilling Program Sitc 742 in Prydz Bay. Antarctica are documented and illustrated. The presence of T/rnln.~.~iosirrr kolhei, 7: tomkirrn, Actir~oc~clrrs ncri~~nc/rilit.r, A. knr.r!rtrii and

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... c ahsencc of Ni!;trlrio irrfr~fri,yid(rric~. 7: itrsigrrrr and E r7ttbrifica in Sample 119-742A-15R-4, 44-46cm constrain its agc to ca. 2.7-1.8 Ma (!:ite Plioccne). Diatoms associated with sea ice cons~ilute 3 5 8 of the I Pliocene diatom nssemblagc, compared with 716 of the modem scdimcnt asscmhlage at the site, snggsling thar sea ice was present during the lnre Plivcene pried of rlrposition of the a~mplc. ;~lthough it prohahly was not thc significant feature it is today. Tlrcrlrrssinsirrr rllitil>nrrr (Donahue) Fenner is described and illus~rr~terl in detail and is validly published. An cxpandcd description I and numerous illustntions arc also presented for 7: romkbrtr Rrady. ~)~i c r o l~n l e n n t o l o~~! 1201. 42. no. 3, 11' 1). 285-302, tpralliprrrr I. p/rrrt:r. 1-8, z~h l r 1, 1996 285 I This article is a U.S. government work, and is not subject to copyright in the United States. A/bcl-t D. M(rhood orld John A. Brrrmn: Lnte Pliocene Dintonis in a Dirrfminite frtln~ Pnldz dzcij: Eosf Anturcticu Nit:sr/rm praeritrta GERSONDE 1991. p. 148. pl. 1, figs. 7-17: pl. 2, Rhi7nsolcniu sp. D nf HARWOOD AND MARUYAMA 1992, p. 705, fig. 5,6. pl. 3, fig. 3.4, pl. 10, fig. 7. pl. 1 X. figs. 7-10 Rrt?rat.k.~: Rare. not recordcd in Table 1 . Apicies rounded, three apical CORtaC turned towards the apex. Gersonde suggests N. prcreclrr-tu is a precursor of N. curtn (Nitrsckin cttrta = Fragi-I~rt-iopsis crrt-[(I). As discussed undcr T: nbliqurcostafa, unti I a detailed SEM study is made of the Fmgilan'opsis, their taxonomic position is in question. Harwood ant! Maruyama (1992) list thc last occurrence of N. pruecm-ta at 3.6 Ma, subslantially dder than the estimated age of Sample 1 19-742A-15R-4, 44-4hcm 12.2-1 .R Ma). RIziznxo!enin Irebetnta f. bidens Heiden Plate 7. figure 8 Rhitmsublilr /tr~l>etnto f. bidetis Hciden in HEIDEN AND KOkBE 1928. -FENNER ET AL.. 1976. p. 778, pl. 13. fig. 8. -JOUSE 1Y77, pl. 8, fig. 18 as R. spp. Remarks: Rare, not recorded in Table 1. Ecolrtgy: Fenner ct al. (1976) rcpnrted this tnxon fmm both Antarctic and subantarctic waten hut note that it had its maximum abundance in the region of the PFZ. Rl~iznsolenia Rebetutu t hiemalis Grnn Plate 7, figures 5,7 Rh~znsolerrin hehet(rto f. Iii~~~rolis GRAN 1905, p. 527, pl. 27, fig 9; FENNER ET AL.. 1876. p. 778. pl. 13, figs. 10-1 2. Rernark.~: Rare, not recorded in Table 1 . Ecolugjh: Fenner et al. (1976) reported this taxon from both Antarctic and subantarctic waters but note that it had its maximum abundance in the region of the PFZ. Rhiznsnkniu s~l i f o m i s Brightwell Platc 1 , figure 7; plate 7, figures 4.7 Rhizflsoleiiia sn1iifonrlis Brightwell. -FENNER ET A t . 1976, p. 779. pl. 13. figs. 3-5.9. -HARWOOD AND MARUYAMA 1992, p. 705, pl. 18. lig. 20. Ecolngy: Fenner et al. (1976) notes that R, s~l i f o n n i s is gener-aIly reported to he a cosmopolitan species. She recorded it in both Antarctic and Subnnlarctic waters. Rhizosolenia sp. D Plate 1 , figures 4a, 4h, 5a, 5h; plate 7, figure 3 Remrrrks: The robust apical end of this distinctive diatom contains irregularly-shaped areolae that are separated by prominent marginal ridges (pl. I, ligs. 4b, 5a, 5b). These ridges are twisted around the apical horn in a screw-like fashion (pl 1, figs. 4b, 5 b). Cnscitrosiln srdluri~ (Rnpcr) Heidcn var. .r-ytn1,nlophorn (Grun.) HEIDEN and KOLRE, p. 47 1. Ecology: According to Hasle et al. (1 98X), S. micmtria.~ is contined to Antarctic waters and is particularly common on or in shclf-ice or in the surrounding plankton. T?~alirssiosira elliptipora (Donahue) Fenner ex Mahaod and Barron Plate 4, figure 3; plate 5, figures 4a-7c; plate 8, figure 6 Thaka.~.riosira ellipripora (Donahuc) Fenner ex Mahood and Barron. Validation: Cosci~iodisc~r.~ ellipripora Donahue, was descrihd in an unpublished (and difficult to obtain) Ph.D, dissertation (Donahuc 1970) and is therefore invalid under Article 29 of the Tntemational Code of Botanical Nomenclature. It is also invalid because Donahue (1970) failed to designated a type (Art. 37, PLATE 4 1,2 Thulassiosircr kolbei (JousE) Geaonde. 1, scale bar = 20prn; 2, scatc har = 20prn, internal. 3 Thalassin.~iru ~llipripom (Donohue) Fenner ex Mahood and Ramon. scale bar = 20pm. internal. 4-5 Thnla.~siosira Ie~~tiginosa (Janisc h) G . Fryxell. 4a, scale bar = 20pm, internal, labiate pmcess (small arrow). strutted process depressions (large arrow):4b, scale bar = 2pm. internal, margin of fig. 4b, strutted process depression (arrow); 5, scale bar = 20vm, labiate aperture (arrow). 7 TI~nlassifisim fetruoesfrupii var reimeri Mahood and Barron. ha, scale bar = 10, labiate aperture (small arrow). central depression with strutted process apcrture (large amw); 6b, scale bar = 2pm, labiate pr0ces.s (small arrow), central strutted process apcrture (large arrow); 7, scalc bar = IOprn. labiatc pmcess (smull arrow), central strutted pmcess (Iarge arrow). Pliocene 1licztum.s br ci D i o t o r n i t e ,~~~~~~