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The greater portion of the present communication is devoted to the consideration of Chelonia, and more especially to specimens from the Cambridge Greensand, most of which were collected nearly twenty years ago by my college friend Mr. T. Jesson, F.G.S., of Northampton. It includes, however, the description of an interesting Chelonian from the Wealden, kindly lent to me by the Rev. P. B. Brodie; and also makes certain redeterminations as to the affinities and serial position of some of the marine Chelonians of the London Clay. The tooth from the Wealden referred to Ornithopsis leads to the consideration of the affinities of some allied specimens from the Portlandian of France. 1. The Genus Rhinochelys, of the Cambridge Greensand. The name Rhinochelys was applied in 1869 by Prof. H. G. Seeley to the Chelonian cranium from the Cambridge Greensand figured by Sir R. Owen in his ‘Cretaceous Reptalia’ (Mon. Pal. Soc.), pt. i. pl. vii. A, figs. 1-3 (1851), under the name of Chelone pulchriceps , of which species it is the type. The distinctive features of this cranium, as shown by the figure, are that the pterygoids, which are in contact throughout their length, are comparatively narrow and emarginate, and that the palatines unite in the median line. There are, moreover, distinct nasals, the prefontals being separated from one another by the nasals and frontals. Again, the temporal fossæ are completely roofed over, after a manner now obtaining only in the Chelonidæ—that is to say, there is both and inferior and

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In view of these changes, special prominence has been given in this volume to the popular titles of the various species, which are less subject to such emendations, and these alone have been employed in the legends to the plates and text-figures.A new feature in the treatment of the group is the large number of forms ranked as sub-species, or races, instead of as full species. The principle of this is that when certain representatives of a genus, or a group of a genus, are more nearly allied to one another than they are to the other members of the same, they are regarded as sub-species.The Asiatic and American wapitis, for instance, are obviously more closely related to one another than they are to the red deer, while the Caspian maral and the North African deer come nearer to the latter than to any other members of the same group. Consequently all the forms of wapiti are classed as geographical races of a single variable and widely spread specific type ; while the European, the Caspian, and the North African red deer are ranked as sub-species of a second.In like manner the numerous modifications of the sambar type show mutual resemblances not shared either by the chital or the para, and all the former are accordingly brigaded under one specific title. Althoughin some cases such geographical races, or sub-species, may pass imperceptibly into one another, the absence of intergradation is not considered any bar to classing any particular form as a sub-species. Where such sub-species are separated by the ocean, such intergradation must obviously have ceased after the disruption of the land connection between their respective habitats.Generic terms are likewise, for the most part, used in a wide sense, although they are frequently split up into minor groups, or sub-genera, which many writers would probably prefer to rank as genera. If, however, genera are used in a more restricted sense we are very apt to lose sight of many broad generalisations. For instance, if Cervus be split up, we lose sight of the fact that all the large brow-antlered deer are essentially an Old World type, with western representatives in the American wapitis.