In the progress of the Geological Survey of the South of Scotland, specimens referable to the genus Eoscorpius have been gradually accumulating. In 1876 J. Bennie, Fossil Collector to the Survey, obtained an example from the Coal-measures of Fife. Since then fragments have been disinterred by him and by A. Macconochie, also Fossil Collector to the Survey, from the Calciferous Sandstone series in the counties of Edinburgh, Berwick, Roxburgh, Dumfries, and Northumberland and Cumberland. It was not till the spring of last year (1880) that they began to be found in such a state as to necessitate a description of the fossils. In the summer of that year A. Macconochie obtained an almost entire example from the neighbourhood of Langholm, in Dumfriesshire. This year (1881) J. Bennie has secured several good though fragmentary specimens from the neighbourhood of Edinburgh, while A. Macconochie has sent in several from the counties of Berwick and Northumberland. In my capacity of Acting Palæontologist, I have had an opportunity of studying these remains, and by the permission of A. C. Ramsay, LL.D., F.R.S., Director General of the Geological Survey of Great Britain, and Professor A. Geikie, LL.D., F.R.S., Director of the Geological Survey of Scotland, I have been allowed to describe them.