The trilobite order Proetida forms a minor but important faunal element within the Ordovician strata of Baltoscandia. This review follows the current systematic, taxonomic, and stratigraphical usage and discusses the distribution of these trilobites within the context of the Confacies Belt model. A database of species-level information was derived from numerous publications relating to the Scandinavian and Baltic states and relevant neighbouring regions. Important additional information on stratigraphical occurrences of genera has been derived from glacial erratic boulders (geschiebe) from northern Germany and adjacent areas. The representatives from Baltoscandia of three superfamilies, Bathyuroidea, Aulacopleuroidea, and Proetoidea, are listed. The genus level was chosen as the most practicable to plot on the maps, one showing the time interval for the Kukruse Regional Stage (or Global Stage Slice Sa1), the other that for the Pirgu and Porkuni stages (or stage slices Ka4 and Hi1-Hi2). These intervals each show a diversity peak within the ranges of about 30 genera of Proetida and over 70 species from the Ordovician successions of Baltoscandia. Out of these a total of nine genera cross the Ordovician-Silurian boundary.The regional comparisons from within Baltoscandia show differences in facies dependency of certain genera, with possibly also a latitudinal component. During the late Ordovician the faunal resemblance appears to be closest to the neighbouring palaeocontinent Avalonia, suggesting a faunal exchange between or pathways to both continents from elsewhere. Besides climatic and geographical proximity of palaeocontinents, sea-level changes also have to be considered in explaining the distribution of Proetida in Baltoscandia.

High resolutional microfacies data from the Beringhauser Tunnel section in the northern part of the Rheinisches Schiefergebirge allow the reconstruction of a relative sea-level curve. Distinctive sedimentological signals in this cephalopod limestone section indicate the positions of sea-level lowstands that correlate well with preexisting sea-level curves. Only slight differences in some lowstand positions have been observed by means of conodont biostratigraphy. The basal Famennian portion of the succession at the Beringhauser Tunnel section exposes microbial sedimentary structures reported from the Rheinisches Schiefergebirge for the first time that are indicative of initial mud-mound formation or mud-mound flanks. Further mud-mound growth with the development of a synsedimentary relief was stopped, probably due to drowning.

Biometric analyses of the trilobite Cyamella stensioei Owens, 1979, from carbonate mud mounds of the Upper Ordovician Boda Limestone of central Sweden, along with a comparison of closely allied rorringtoniid taxa from outside Baltoscandia, reveal important systematic and ecological information on this proetide taxon. Biometric analysis of the cephala of C. stensioei shows a number of instars, reflecting several ontogenetic stages, and a meraspis stage of this taxon is figured for the first time. C. stensioei is exclusively found in mass accumulations in the former, open cavities of the carbonate mud mound and was therefore most likely a cavity-dweller, possibly adapted to this lifestyle through chemosymbiosis. Some of the cavities are interpreted as former seepage conduits. Comparison of C. stensioei with other rorringtoniid trilobites suggests possible ancestors occurring in South China and Sibumasu terranes, determined earlier as Decoroproetus sp. and Cyamella sp., all differing from the genus Paracyamella, which is reassessed here. In wider terms of ancestry, they originate from Baltica or Laurentia, where the first rorringtoniids are known from the middle Darriwilian.

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Auf Grund eines Versehens wurde die Abb. 4 im Beitrag GEYER et al. (Pal~iontologische Zeitschrift 78 (1): 127-136) falsch beschnitten. Daher wird an dieser Stelle eine korrigierte Version nachgeliefert.