Since the publication of my “Report” in December 1899, Mr Tait, fossil collector to the Geological Survey of Scotland, has been successful in adding a number of specimens of great interest to the valuable series of Scottish Silurian Fishes which supplied the material for that memoir, and with the permission of the Director of the Survey, to whom my best thanks are due, I propose to give descriptions of them in the following Supplement. The search for these remarkable fishes has likewise been taken up by private collectors, and I have therefore pleasure in acknowledging my indebtedness to Messrs J. Young, of Lesmahagow, P. Macnair, of Glasgow, A. Whyte and F. White, of Muirkirk, and D. Nimmo, of Hamilton, for kindly submitting to me the material resulting from their own work in this field.