Pygocephalus Cooperi was first described by Professor Huxley from the Coal-measures of Paisley in 1857 (Quart. Journ. Geol. Soe., vol. xiii, pp. 363–369, pi. xiii), and a second specimen by the same author in 1862 (op. cit., vol. xviii, pp. 420–422, text-figure). Some additional specimens came into my hands for exami-nation, and were communicated to the Glasgow Geological Society, in 1866 (Trans. Geol. Soc. Glasgow, vol. ii, pp. 234–247, pi. iii, figs. 1–3). In that paper I described a second species, which I named Pygocephalus Huxleyi (text-figure, p. 244, op. cit.). The specimens referred to above were obtained from the Coal-measures of Paisley, from Kilmaurs, and from near ilanchester. Since then the late Mr. Henry Johnson, F.G.S., formerly of Dudley, obtained

many examples of Pi/gocephalus from the Clay-ironstone nodules of Coal-measure age at Coseley, near Dudley, now in the Geological Department of the British Museum (Natural History Branch), Cromwell Itond, S.VV. These specimens are preserved in great perfection, and I had fully intended to figure them some years ago, but the pressure of other work caused them to be set aside for a time. Last year I received an example of Pygocephalm from Mr. Walter Baldwin, P.G.S., obtained from the Clay-ironstone of the Middle Coal-measures at Sparth. Rochdale (for description see Fig. 1, p. 405). I have also received through Mr. H. A. Allen, F.G.S., of the Geological Survey Museum, Jermyn Street, by the kindness of their owner, Mr. Herbert Hughes, Assoc. E.S.M., F.G.S., of Horseley House, Volverhampton Street, Dudley, four most interesting specimens of Pygocepkalus collected by him, two of which prove to be females, a point of extreme interest not heretofore observed.