Amberg, Chloé E.A ; Molyneux, Stewart G ; Zalasiewicz, Jan A.
https://nora.nerc.ac.uk/id/eprint/533859/1/chitinozoan-biostratigraphy-of-the-regional-arenig-series-in-wales-and-correlation-with-the-global-lower-middle-ordovician-series-and-stages.pdf.  , 2023