The Arenig Fawr area of North Wales constitutes the type area for the British Lower to Middle Ordovician Arenig Series and is complemented by sections in the Carmarthen and Whitland areas of South Wales. We describe chitinozoan assemblages from both areas in order to aid correlation of the Arenig Series in its type region with the global Ordovician series and stages. Chitinozoans recorded from Arenig Fawr provide permissive rather than conclusive evidence but suggest that the Henllan Ash Member correlates with the upper Floian Stage Slice Fl3 or lower Dapingian Stage Slice Dp1. Better results were obtained from South Wales where six chitinozoan assemblages are distinguished, ranging in age from late Tremadocian to middle Darriwilian (early Llanvirn). Most species are known from South China, Gondwana and/or Baltica where there are controls on ranges. They show that much of the lower Arenig (Moridunian) succession in South Wales correlates with the upper Floian Stage (Fl3). Correlatives of the lower and middle Floian Stage (Fl1, Fl2), if present, must be represented by the Ogof Hên Formation and lowest Carmarthen Formation. Chitinozoan assemblages from the upper Arenig Series (Fennian Stage) are more readily correlated with Gondwanan biozones and indicate correlation of the Fennian Stage with the Dapingian and lower Darriwilian (Dw1) stages. The middle Arenig Whitlandian Stage is constrained in South Wales to an interval from the uppermost Floian Stage to the basal Dapingian Stage, resulting in an inferred increased rate of sediment accumulation.

Figure 3 from the above article was erroneously published upside down. Please see below the correct version of the figure. The publishers apologise for this error.

Systematic collecting through the upper Wenlock (upper Homerian) and lower Ludlow (Gorstian and lowermost Ludfordian) Silurian rock succession of the Long Mountain, Powys, Wales, identifies some 48 chitinozoan species that distinguish four biozones, two subzones and an interregnum. Consideration of the chitinozoan biozones together with those of the graptolites enables a local three-fold subdivision of the late Homerian lundgreni graptolite Biozone, and the distinction of lower and upper intervals for the Gorstian incipiens graptolite Biozone. The base of the Ludlow Series in the Long Mountain more or less equates to the base of the Cingulochitina acme chitinozoan Biozone, although no key chitinozoan first or last appearance datums are associated with the series boundary itself. The new graptolite–chitinozoan biozonation allows enhanced correlation between upper Wenlock and lower Ludlow sedimentary deposits of the Lower Palaeozoic Welsh depositional basin and those of the palaeo-shelf in the stratotype Wenlock and Ludlow areas of Shropshire. Chitinozoans seem affected by the phenomena that caused the late Wenlock ‘Mulde extinction’ in graptolites but, with the final disappearance of 9 species and re-appearance of 11 species following an interval of overall low diversity, they seem to have suffered less severely than their macro-zooplanktonic contemporaries.

New chitinozoan data are presented from the classical section along the Onny River in the type Caradoc area, and from the deeper-water sections in the Shelve area, including the former British candidate GSSP for the base of the Upper Ordovician Series. The rich and well-preserved chitinozoan fauna of the Onny River has been a standard for 40 years, but new data revise some of the identifications. The assemblages are now attributed to biozones that are more readily applicable for international correlation. The main part of the section can be interpreted as belonging to the originally Baltoscandian Spinachitina cervicornis Biozone, although this is uncertain in the lower part. Within this biozone, the Fungochitina actonica Subzone has been defined. The Onny Formation at the top of the section is equated with the Acanthochitina latebrosa–Ancyrochitina onniensis Biozone; contrary to earlier reports, Acanthochitina barbata is absent. The Lower Wood Brook and Spy Wood Brook section from the Shelve Inlier yielded a great number of moderately to well-preserved chitinozoans, but a low-diversity assemblage. Their ranges have been neatly positioned against the well-known graptolite stratigraphy in the area. A local Eisenackitina rhenana Biozone? has been recognized, allowing us to suggest some international correlations.

To help calibrate the emerging Upper Ordovician chitinozoan biozonation with the graptolite biozonation in the Anglo-Welsh, historical type basin, the graptolite-bearing Caradoc–Ashgill successions between Fishguard and Cardigan, and at Whitland, SW Wales, have been collected for chitinozoans. In the Cardigan district, finds of Armoricochitina reticulifera within strata referred to the clingani graptolite Biozone (morrisi Subzone), together with accessory species, indicate the Fungochitina spinifera chitinozoan Biozone, known from several Ordovician sections in northern England that span the base of the Ashgill Series. Tanuchitina ?bergstroemi, eponymous of the succeeding chitinozoan biozone, has tentatively been recovered from strata of Pleurograptus linearis graptolite Biozone age in the Cardigan area. The T. ?bergstroemi Biozone can also be correlated with the type Ashgill Series of northern England. Chitinozoans suggest that the widespread Welsh Basin anoxic–oxic transition at the base of the Nantmel Mudstones Formation in Wales, traditionally equated with the Caradoc–Ashgill boundary, is of Cautleyan (or younger Ashgill) age in the Cardigan area. In the broadly time-equivalent, graptolite-rich Whitland section, also in SW Wales, two Baltoscandian chitinozoan biozones and a subzone have been recognized (again using accessory species), namely the Spinachitina cervicornis Biozone?, the Fungochitina spinifera Biozone and the Armoricochitina reticulifera Subzone. The new chitinozoan data provide a more precise means of correlation between the Whitland and Cardigan successions and suggest that the Normalograptus proliferation interval of the Whitland section is at least partly attributable to the Dicellograptus morrisi Subzone of the Dicranograptus clingani Biozone, rather than equating with the overlying Pleurograptus linearis Biozone.

The lower Williamson Shale at Tryon Park, Rochester, New York State is unique in the co-occurrence of Stimulograptus clintonensis (Hall), previously recorded only from the middle Telychian, and Pterospathodus amorphognathoides amorphognathoides Walliser, previously recorded only from the upper Telychian (Cyrtograptus lapworthi Biozone and higher). These two co-occurring fossils are clearly providing contradictory ages for the lower Williamson Shale. The incorporation of chitinozoan data from both the Williamson and Willowvale shales does not support unequivocally either the graptolite- or conodont-derived biostratigraphy and thus the age of the lower Williamson Shale remains problematical.

Forty-six samples, taken from the Upper Ordovician and lower Silurian strata of the Girvan district, Midland Valley of Scotland, yield moderately well-preserved and diverse assemblages of chitinozoans. The area was chosen to study the composition of the chitinozoan assemblages, rarely described before in Scotland, which lay at the south-eastern margin of the Laurentia palaeocontinent. These assemblages are compared with those of the same age on other palaeocontinents, representing a critical time when both the Iapetus and Tornquist oceans were closing, thus forming the Caledonide and associated orogens. It is possible to correlate the chitinozoan occurrences at Girvan with those of other parts of Laurentia (Quebec area), other palaeocontinents such as Baltoscandia (Sweden, Estonia), Avalonia (Wales, Brabant Massif) and some parts of Northern Gondwana (Saudi Arabia). For the lower Silurian, it is possible to correlate with the global chitinozoan biozonation, and a calibration between the chitinozoan occurrences and the graptolite biozonation of Girvan is established. Several levels within the Balclatchie, South Shore, Three Mile, Shalloch, Wood Burn, Lauchlan, Drumyork Flags and other formations are accurately dated.

The new standard conodont zonation includes, in succession from below: Lower Ps. bicornis Zone, Upper Ps. bicornis Zone, Lower P. procerus Zone, Upper P. procerus Zone, Lower K. ranuliformis Zone, Upper K. ranuliformis Zone, 0. s. rhenana Zone, Lower K. walliseri Zone, Middle K. walliseri Zone, K. patula Zone, uppermost K. walliseri range, post K. walliseri interregnum, K. o. ortus Zone and 0. s. sagitta Zone. Lower boundaries for each zone are defined or redefined. A less detailed biostratigraphic nomenclature at the superzone level is suggested for use where collections are inadequate: The Pterospathodus Zonal group, the Upper Pterospathodus Zonal group, the P. amorphognathoides Zonal group, the Ps. bicornis Superzone, the P. procerus Superzone, the K. ranuliformis Superzone, the O. s. rhenana Superzone, the K. walliseri Zonal group, the Upper K. walliseri Superzone and the K. o. ortus Superzone. These partly overlap and can be used according to the taxa present. The proposed zonation is applied to most known conodont sequences. The taxonomic concept of the taxa used is discussed; new taxa include Nudibelodina sensitiva, Ozarkodina paraconfluens and O. martinssoni. The species name Ozarkodina ortus is a senior synonym of Kockelella absidata.