Abstract
Acritarchs and chitinozoa are used to date Ordovician rocks in England and Wales, but the data-base for both groups is poor. Study of chitinozoa has been neglected in the UK, in contrast to North America and southwest Europe where biozonations have been established. Formal definition of acritarcb biozones may soon be possible in the Tremadoc–Arenig, but acritarch biostratigraphy in the Llanvirn–Ashgill is insufficiently documented.