Five goniatite species, of which two are new, are described from the Plb subzone of the Upper Viséan shales of Dough Mountain, Co. Leitrim, Ireland. These species are diagnosed mainly on the test ornamentation which is claimed to be continuously variable and is arbitrarily divided into stages. Goniatites, the mature orna¬ment of which belongs to a particular stage, are named as separate morphological species. The succession of ornament stages constitutes a trend which has operated upon a primitive stock both in B2 and Plb times. This has led to the production of homeomorphs the separation of which is important in stratigraphical studies.