Abstract Even though the ostracod-like fossils that occur in Cambrian rocks are now excluded from the Ostracoda as strictly construed, they are included in the present volume to complete the stratigraphical record of such animals in British rocks. These Cambrian ostracod-like forms are currently referred to the orders Bradoriida Raymond, 1935 and Phosphato-copida Müller, 1964. Originally Raymond (1935) established the Order Bradorina ( sic ) to include all Cambrian ostracod-like forms. Muller (1964) subdivided the Bradoriida into the suborders Phosphatocopina, which he consided to have primary phosphatic carapaces, and Bradoriina, supposedly with chitinous or calcareous carapaces. In 1982 Müller raised both these groups to ordinal level; such a classification based on carapace composition is, however, untenable ( Siveter & Williams 1997 ). Phosphatocopids were first considered to be early ostracods ( Muller 1964, 1979 ; Jones & McKenzie 1980 ), but, based on more recent evidence from soft parts, they are now known to be the sister group of the Eucrustacea ( Walossek 1999 ; Siveter et al. 2001, 2003 ; Maas et al. 2003 ). The Bradoriida (sensu Muller 1982 ) are probably a polyphyletic group that may include ancestral ostracods together with other crustacean or arthropod groups ( Jones & McKenzie 1980 ; Hou et al. 1996 ). Hinz-Schallreuter (1993b, 1998, 2000) , who preferred to encompass both bradoriids and phosphatocopids under the name ‘Archaeocopa’ ( ex Archaeocopida Sylvester-Bradley, 1961), characterized the order as an 'ostracod group' distinct from 'true ostracods' by

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