The new retiolitid graptolite Kirkigraptus inexpectans gen. et sp. nov., from the Neodiversograptus nilssoni Biozone of the Bartoszyce borehole, Poland is described. It is unique among the retiolitids not having a preserved virgella or ancora. Instead the most proximal structures are two round proxi-lateral lists, joining the two genicular lists of the first thecae, connecting the two sides of the rhabdosome. The lists are interpreted as a possible homologue of the distal edge of the ancora umbrella in typical retiolitids. The size of rhabdosome with large proximal lateral orifices, and the ventral panels of thecae with mid-ventral lists, are similar to those of Plectograptus, whereas the two ancora sleeve panels consisting of spaced horizontal lists only, resemble those of Valentinagraptus. It is possible that the new retiolitid may represent a new pattern of development of the proximal end of the rhabdosome, different from that in all other retiolitids.

Key words: Graptolithina, Retiolitidae, Kirkigraptus, ancora, proxi-lateral list, Silurian.

Anna Kozłowska akd@twarda.pan.pl, Instytut Paleobiologii PAN, ul. Twarda 51/55, PL-00-818 Warszawa, Poland; Denis E.B. Bates deb@aber.ac.uk, Institute of Geography and Earth Sciences, University of Wales, Aberystwyth Ceredigion SY23 3DB, UK.