It would be difficult after the closest investigation to add much to the exhaustive list of species given in the excellent paper on this subject which was read by Mr. Swanston before the Belfast Naturalists Field Club some twenty-five years ago. In that paper reference is made to the classification by the Geological Survey of the rocks of the district, under the general heading of Lower Silurian. Subsequently to the publication of the maps of the area, the information as to the Silurian fauna was greatly extended by the labours of Professor Lapworth and Mr. Swanston, to whom science is so largely indebted. The completion of the one-inch Geological Map of Ireland enabled the revision of work done in the earlier stages of the Survey's existence to be undertaken, and in this revision the North-East Silurians were amongst the first dealt with, and I was detailed to search the most promising localities for fossils, and to zone the beds in which they might occur.