Five years have elapsed since I completed the description of a very interesting fossil from the lower Carboniferous shales of Ayrshire and Lanarkshire, with the assistance of Mr. H. M. Jenkins, F.G.S. The results of our labours were read before the Royal Society on June 17, 1869, and were subsequently published in the Philosophical Transactions, vol. clix. p. 693 (1869), under the title of “On Palæocoryne , a genus of Tubularine Hydrozoa from the Carboniferous formation.” In 1872 Dr. Allman (Monograph of the Hydroida, Ray Society, vol. ii. pp. 172 & 173) criticised the zoological position we had assigned to the fossil, and, whilst expressing his satisfaction concerning the manner in which it had been described and delineated, gave also his reasons for not including Palæocoryne amongst the Hydroida. Some of these reasons, which are stated with Dr. Allman's usual clearness and force, had occurred to us during the difficult task of assigning a classificatory position to the form; and we wrote ( op. cit. p. 695), “Were it not for the calcareous investment, there would be no difficulty in admitting the fossil amongst the Hydrozoa: and had we not been able to avail ourselves of the affinities of the very anomalous genus Bimeria (Wright), the difficulty could hardly have been overcome.” Lately Mr. R. Etheridge, jun., F.G.S., of the Geological Survey of Scotland, has forwarded to me a great number of fragmentary specimens of Palæocoryne derived from the lower Carboniferous shales. These specimens explain certain points of anatomy upon which there