The new retiolitid species, Spinograptus tubothecalis, is described from the Colonograptus praedeubeli and C. deubeli biozones from two localities in Poland: a borehole on the East European Platform and the Holy Cross Mountains. This was a recovery phase after the severe Silurian Cyrtograptus lundgreni Event. The new species has a unique, previously undescribed form of finite rhabdosome. Unlike the species Spinograptus reticulolawsoni and S. lawsoni, in which the finite rhabdosomes taper distally, its rhabdosome is parallel−sided with the two distal thecae developed as isolated tubes without genicular processes, with a small appendix between them. The new species also has preserved membranes of the sicula, thecae and ancora sleeve, similar to a few species of Spinograptus from the lower Homerian. Spinograptus tubothecalis, like Spinograptus clathrospinosus and S. spinosus, has paired reticulofusellar genicular processes on the pre−thecal ventral orifices, similar to but shorter than thecal processes. Transverse rods, a rare character in post−Cyrtograptus lundgreni Event retiolitids occur in the new species in rudimentary form.

Key words: Graptoloidea, Retiolitidae, Spinograptus, finite colony, Silurian, Poland.

Anna Kozłowska [akd@twarda.pan.pl] and Kinga Dobrowolska [kdobrowolska@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, Aberystwyth University, Aberystwyth, Ceredigion SY23 3QQ, UK .