(also Llandeilo stage; named after the population center of Llandeilo, county of Carmarthenshire, Wales, Great Britain), the fourth stage from the bottom in the Ordovician system. It was identified in 1829 by R. Murchison. The type section is composed of flagstones, marls, and limestones characterized by trilobites, brachiopods, and conodonts of the Pygodus anserinus and Amorphognathus tvaerensis zones. Deposits of the Llandeilian stage are distributed in numerous Western European countries (Great Britain, France, Czechoslovakia, Poland, Sweden, and Norway), the USSR (Estonian SSR, Leningrad Oblast, the Urals, Kazakh SSR, Kirghiz SSR, southern and central Siberia, and the Northeast), the United States, South America (Argentina and elsewhere), Australia, People’s Republic of China, and Burma.