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Introduction
The extended and varied assemblage of erratic Ordovician sponges in Germany and the Netherlands has been subject of numerous studies, from the first decades in the 19th Century, such as by Goldfuss (1826), Klöden (1834), Roemer (1861), Quenstedt (1878) and Rauff (1893-1894, 1895), to recent studies, such as those by Van Kempen (1978), Von Hacht (1990), Von Hacht & Rhebergen (1997), Rhebergen et al. (2001) and Rhebergen (2009). The provenance of the sponge assemblages has been discussed in many papers, but has not been achieved exactly. There is more and more evidence that they originate from the eastern Baltic, considering similarities with sponges from bedrock in Estonia and the St. Petersburg region.
The notes in the present short paper refer to three sponge species, all of them included in this assemblage. Better preservation of skeletal elements in new material and renewed examination of sponge collections, which have as yet remained unnoticed in the European and American literature, lead to corrections of the systematic position of two sponge species. In addition, a new repository of the holotype of a third species is reported herein.