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