. Bulletin of the British Museum (Natural History), Geology. %J. Figs 1—4 Chitinozoans and acritarchs from Dob's Linn. 1, Ancyrochitina ancyrea (Eisenack 1931) Eisenack 1955. SU/DL/41, acumunatus Zone, Main Cliff, x 250. 2, Cyathochitina kukersiana (Eisenack 1934) Eisenack 1965. SU/DL/9, anceps Zone, Main Cliff, x 250. 3, Solisphaeridium nanum (Deflandre 1945) Turner 1984. SU/DL/12, anceps Zone, Main Cliff, x 530. 4, Diexallophasis sp. 1. SU/DL/10, anceps Zone, Main Cliff, x 470. Both groups of palynomorphs are unevenly distributed throughout the two sections although they are generally more a
. Bulletin of the British Museum (Natural History), Geology. %J. Figs 1—4 Chitinozoans and acritarchs from Dob's Linn. 1, Ancyrochitina ancyrea (Eisenack 1931) Eisenack 1955. SU/DL/41, acumunatus Zone, Main Cliff, x 250. 2, Cyathochitina kukersiana (Eisenack 1934) Eisenack 1965. SU/DL/9, anceps Zone, Main Cliff, x 250. 3, Solisphaeridium nanum (Deflandre 1945) Turner 1984. SU/DL/12, anceps Zone, Main Cliff, x 530. 4, Diexallophasis sp. 1. SU/DL/10, anceps Zone, Main Cliff, x 470. Both groups of palynomorphs are unevenly distributed throughout the two sections although they are generally more abundant at Main Cliff. Acritarchs appear to be more important and better preserved in the grey mudstones, while chitinozoans appear to be more common in the black shales, although this is not always the case. Palynomorph colour varies from grey to black within a single sample, and probably reflects differences in wall thickness. Acritarchs can be divided into several groups (Downie et al. 1963): (a) Sphaeromorphs which are spherical. These are of limited biostratigraphical use as can be seen in Figs 1 and 2, and will not be mentioned further; (b) Acanthomorphs which have spines or processes; (c) Herkomorphs which have crested ridges forming polygonal fields; (d) Polygonomorphs which have a limited number of processes, usually between three and five; and (e) Netromorphs which are generally fusiform in shape. The Dob's Linn samples are noticeably dominated by acanthomorph acri- tarchs and only a few samples contain representatives of the other groups. Anceps Zone Six samples have been studied from Main Cliff (only one of which is a grey mudstone) and sixteen acritarch and chitinozoa taxa have been found (Fig. 5). The chitinozoans Cyathochitina campanulaeformis (Eisenack), C. kukersiana (Eisenack) and Rhabdochitina gallica Taugourdeau all suggest a Caradoc to Ashill age. Hercochitina cf. turnbulli Jenkins has previously been described from the Caradoc of Oklahoma (Jenkins 1969),
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