384 Mr. W. J. Sottas on the Flint Plate XVII. Fig. 1. Membranipora polita, n. sp. Fig. 2. Membranipora pedunculata, Manzoni. Fig. 3. Sehizoporella sanguined, Norman, var. Fig. 4. Microporella Jissa, n. sp. jFfy. 5. Porella roxtrata, n. sp. 5 a. Young cells showing the tridentate lower margin of the orifice. Fig. 6. Membranipora corbula, n. sp. Fig. 7. Mucrondla tubulosa, n. sp. XLVII. — On the Flint Nodules of the Trimmingham Chalk. By W. J. Sollas, M.A., F.R.S.E., F.G.S., Professor of Geology in University College, Bristol. [Plates XIX. & XX.] Personal. — In 1873 Mr. Jukes-Browne gave me some very in-teresting specimens of flint nodules which he had obtained from the chalk of Trimmingham, Norfolk. To the examination of these I devoted a great part of the summer of 1874, preparing some hundreds of drawings of the sponge-spicules which are associated with them. After a visit to the Trimmingham cliffs together, my friend Jukes-Browne and I arranged to write a joint paper on them, he undertaking their general geology and leaving the description of the flints to me. Jukes-Browne's paper was ready for publication a year or more ago; but mine seemed in danger of indefinite postpone-ment, when I heard from Mr. G. Jennings Hinde, F.G.S., that he too was at work on the same or a very similar sub-ject. This led me to embody my results in the following paper, which was read before section C of the British Asso-ciation during its meeting at Swansea this summer. It will appear as an abstract in the Annual Report, and is given here in full as a sequel to Mr. Jukes-Browne's, which appeared in the ' Annals ' of last month. The Flint Nodules. — In form they vary greatly : some are flabellate, some irregularly conical ; others consist of a some-what ellipsoidal body seated on a short stalk, while many are irregular and amorphous. They consist of chalk and silex in various proportions ; sometimes the chalk forms the greater part of a nodule, sometimes it is altogether absent. Between a nodule consisting of a solid mass of silex, black throughout, except on the surface, and one consisting chiefly of siliceous chalk there are any number of others forming a complete transitional series. Commonly the flint is traversed by a number of winding anastomosing passages, which are occu-
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