Two areoligeracean dinoflagellate cysts from the Carstone Formation (Lower Cretaceous) at Middlegate Quarry, North Lincolnshire, UK

Five Lower Albian (Lower Cretaceous) areoligeracean dinoflagellate cyst species are present in the Carstone Formation at Middlegate Quarry, North Lincolnshire, UK; Canninginopsis monile, Circulodinium deflandrei, Cyclonephelium compactum, Cyclonephelium intonsum and Cyclonephelium longispinatum. The taxonomy of Circulodinium deflandrei is reviewed with respect to 20 measured Carstone specimens. The taxonomy of Cyclonephelium longispinatum is reviewed with respect to 70 measured Carstone specimens, and a study of 40 measured specimens from its type material in Site 361, Deep Sea Drilling Project Leg 40, offshore south-western Africa. Circulodinium deflandrei and Cyclonephelium longispinatum have recently been considered by other workers to be junior synonyms, respectively of Circulodinium hirtellum and Tenua anaphrissa. However, following detailed study of their morphologies, the synonymies are formally rejected here. An emended diagnosis is given for C. longispinatum. A re-assessment of stratigraphical ranges of taxa co-occurring with the type material of C. longispinatum is consistent with a Late Albian to Early Turonian age range in Site 361.