Although the Upper Ordovician shelly faunas of South Pembrokeshire (Avalonia at that time) have been studied for over 150 years, the brachiopods have never before been properly documented.  This monograph erects 16 new species and substantially revises the systematics of the rest of the brachiopod fauna (about 75 species in all).  The faunas are compared with other contemporaneous Avalonian brachiopod assemblages, and two major faunal turnovers are recognised.  Implications for understanding better the palaeogeography of Avalonia, Laurussia, Baltica, and north-western Gondwana are discussed.