Abstract Recent studies on British Ordovician ostracods have considerably helped to redress the neglect they suffered after the initial flurry of descriptions of species that were made more than 100 years ago. The British Ordovician holds a large, diverse ostracod fauna that has proven value in biostratigraphy and palaeogeo-graphy. Moreover, several of its faunas remain to be documented, thus offering potential additional rewards. The British Ordovician has representatives of each of the maj or orders of ostracod (for which see Whatley et al. 1993 ), except the Myodocopida. Most ostracod species of the Ordovician belong to the distinctive Order Palaeocopida, whose valves have a straight dorsal margin, are lobate and typically exhibit presumed sexual dimorphism of the shell. The basal Ordovician Tremadoc Series in Britain contains a few species of the Order Bradoriida Raymond, 1935, a taxon historically assigned to the Ostracoda but which most authors now consider to consist of two non-ostracod bivalved arthropod groups, namely the bradoriids sensu stricto and the phosphatocopids (see, for example, Hou et al. 1996 and references therein; Siveter & Williams 1997 ; Williams & Siveter 1998 ; cf. Hinz-Schallreuter 1998). In order to provide complete coverage of ostracods of traditional usage, and also to be consistent with the Cambrian part of this volume ( Rushton et al. 2009 ), the bradoriids of the British Ordovician are also treated herein. There are no known phosphatocopids in the British Ordovician. Recognition of homologies of lobes, sulci, various ventral ridges and other morphological features

Abstract >The Early Palaeozoic history of England and Wales was substantially influenced by the separation of Avalonia from Gondwana and its subsequent migration towards Laurentia. At the start of the Early Palaeozoic, the vast palaeocontinent of Gondwana straddled the South Pole and extended northwards into low latitudes. On the margin that hosted North Africa and North and South America there were areas of crust that were later to become detached terranes. The largest of these was Avalonia, the remnants of which now extend from NE USA, through the Atlantic Provinces of Canada and through England and Wales to Belgium and North Germany ( Cocks 2000 ). Elsewhere, at lower latitudes on the Gondwana margin, there were crustal segments that were later to become the terranes of Armorica (Britanny, Normandy and the Massif Central regions of France), Perunica (much of central Europe, but mainly preserved in the Bohemian part of the Czech Republic) and Iberia (Spain). In addition there are some smaller continental fragments whose history is difficult to establish. The area of England and Wales lay within Eastern Avalonia, which consisted of an initial crustal fragment that separated from Gondwana ( Fig. 3.1a ) and then accreted smaller terranes as it moved towards Laurentia. The core Avalon Terrane was probably assembled by accretion of crustal fragments on the Gondwana margin in the Late Precambrian or early Cambrian. At about the same time, this terrane accreted both the basement of the Welsh Basin ( Woodcock & Gibbons 1988 ) and an amalgamation