The Tertiary Entomostraca (Ostracoda) of England, at first treated of in a monograph for the Palæontographical Society in 1856, were revised in the Geological Magazine, 1870, pp. 155–159. The researches of G. O. Sars and G. S. Brady, elucidating the relationships of the genera and species, gave effect in a great degree to that revision; and their continued labours have further helped us.

I have read with much interest the two articles which Messrs. G. A. Boulenger and R. Lydekker have recently published in the Geological Magazine, and I should be very much obliged if you would permit me to make an addition, which appears to me useful, and which I should be glad to see published.

1. Pseudotrionyx.—1. I have remarked with satisfaction that it has been possible for the above-named naturalists to refer to P. Delheidi, a Tortoise of the London-clay. This discovery is doubly interesting, in the first place because it shows the existence of the Belgian fossil in England, in the second place, because it establishes the existence of the Bruxelliau (Middle Eocene) Chelonian in the Ypresian epoch (Lower Eocene).

I have had occasion lately to thoroughly investigate these and other allied Ammonites, partly because it has been important to me that I should know the true affinities of these species, partly because my attention was directed to certain still obscure points with regard to their identification, and partly on account of the statement by the late Dr. Wright that Am. serpentinus and Am. falcifer were the same species. In pursuing my investigations I have received a great deal of assistance from Dr. E. Hang's Beiträge zu einer Monographie der Ammoniten-gattung Harpoceras, which I am pleased to acknowledge, although I do not find myself able to agree with him in one or two small points which I will presently mention. Meanwhile, by the aid of a few references to well-known works, I will indicate the Ammonites so that they may be understood.

During a recent examination of the lead-mines of Derbyshire, I was interested in some accounts of explosions which had taken place, which were not due either to any material used by the workmen or to fire-damp. Though at first inclined to believe that the accounts were exaggerated, I soon found that not only was the evidence of such explosions having constituted a real danger to the men overwhelming, but that accidents are still liable to occur from this cause. The explosions are connected with the structure known as slickenside in the veins.

In the Woodwardian Museum is a collection of nearly a thousand rock-specimens made by Professor Henslow to illustrate his “ Geological Description of Anglesea ” (1821, Trans. Camb. Phil. Soc. vol. i. pp. 359–452, plates xv.–xxi.). Specimens of the principal dykes were submitted to the examination of Professor Cordier, and his remarks on them are quoted in Henslow's paper. As Cordier's determinations date from a time when thin slices of rocks were unknown, and but little attention has since been given to the dykes of Anglesey, it is believed that brief notices of some of the typical rocks from localities easity identified may have an interest for British geologists. As regards the mode of occurrence of the dykes and their effects upon the adjacent strata, little can be added to the accurate descriptions of Henslow, written at a time when the igneous origin of dykes was a proposition to be proved.