Upper Ordovician Bryozoans from Ojl Myr, Gotland, Sweden

A revision is given of the bryozoan fauna described by Wiman (1901), from a series of glacial erratic boulders found in Oj l Myr, Gotland, Sweden. The fauna is of Late Ordavieian age, and correlates weil with the Porkuni Stage in Estonia, probably most closely with its younger part. Twenty-five species are described, eight of them new: Ceramopora hennigi, Ceramopora corniforme, Bactropora solida, Eridotrypa peculiare, Areanapara (?) wimani, Ptilodichtya irregularis, Cyclophaenopora minor and Cyclophaenopora annulata. A new species, Cyclophaenopora robusta, has been made on weil preserved material, from the Middle Ordavieian of Sweden. A new genus, Cyclophaenopora, and a new family, Nematotrypidae, have been erected. A discussion of the classification of Ordavieian bryozoans is given and a provisional scheme suggested, based on the observations on both the Ojl Myr material, and weil preserved material from the Ordavieian and Silurian of other areas. The cryptostomes are divided according to the three main units used by Astrova & Morozova (1956), hut because this classification is largely artificial, each unit is subdivided into a central group, assumed to be genetically related, and other forms (the unit incertae sedis), which are placed in the unit according to externat morphology and convention. The general chapters include discussions on the budding pattern as a possible a id in classification, and a description of various types of zooecial specialisatians and zoarial appendages, som e of which ma y be related to reproduction. The available evidence points to a relationship of the cryptostomes with the other stenolaematous groups. The anatomy of the peculiar jointed base of the Ptilodichtyidae has been studied, and a functional anatomical explanation is given. A review of the occurrence of phosphatic bodies in Ordavieian and Silurian bryozoans is given, based in part on the Oj! Myr material, and studies of other material. The physiological importance of the various phosphatic bodies is also discussed. A discussion is given on the use of zoarial form in early Palaeozoic bryozoans for palaeoecological analysis. In spite of the poor preservation of histological detail, the shapes of the colonies are often weil preserved, and can be studied free of sediment and post-depositional deformation. The Oj l Myr fauna is used as an example of an analysis of this type; i t is concluded that i t lived in quiet water, on a soft bottom, perhaps within the photic zone