Lower Ordovican acritarchs from successions in England and North Wales.

One hundred and thirty eight acritarch taxa are described from the organic residues of samples collected in North Wales, Shropshire, and the Lake District. The species occur in one or more of 16 microfloral assemblages, selected from 88 prepared samples. Three new genera and seven new species are proposed. Range charts are presented which show the occurrence and distribution of all the species described in detail. On the basis of these results, five microfloral zones and two subzones are proposed. Each zone or subzone is characterised by an assemblage of species, and equates to part of the established Lower Ordovician graptolite zonation. The proposed biostratigraphical scheme is applied to microfloral assemblages from several localities in the English Lake District, most of which were either previously undated or doubtfully dated. Comparisons are made with Arenigian and Llanvirnian assemblages described from the European area, by other authors. Tentative conclusions are drawn as to the possible continuity of the British province with other European areas during Arenigian and Llanvirnian times. Factors affecting the preservation of acritarchs are discussed and a visual classification scheme is presented which takes into account fragmentation, degree of corrosion, and colour.