ABSTRACTThe Desertcreat Group of Pomeroy, Northern Ireland, comprises the Bardahessiagh Formation (Caradoc), the Killey Bridge Formation (lower Ashgill) and the Tirnaskea Formation (upper Ashgill); and unexposed Junction beds are placed between the Bardahessiagh and Killey Bridge formations on faunal grounds. In the systematic study of the brachiopods some 136 forms, including 16 new species and 3 new subspecies, are referred to 102 genera (6 new) and 5 subgenera (1 new). The Bardahessiagh and Killey Bridge Formations can be correlated accurately with horizons in Scotland and America; the Tirnaskea Formation contains theHirnantiafauna and is conformably overlain by the graptolite-bearing Little River Group (Lower Silurian).