terminal joint, were probably furnished with hoof-like claws. Thus, as regards its affinities in the order Rodentia, _Mesotherium_ presents resemblances in its lower jaw (as also in some peculiarities of the skull), and in the articulation of the heel with the shank, to the Hares; while in the shortness of the incisors and some other cranial peculiarities, the form of the shoulder-blades, and the probably hoof-like character of the claws, we may notice an approach to the Cavies, which are also South American forms, and especially to the Capybara, which it probably resembled in its habits, although, if the evidence of the Beaver-like shoulder-blade and humerus be taken into account, it would appear to have been still more aquatic. On the other hand, the resemblance to certain other Mammalia, and especially to some aberrant Ungulates, is unmistakable. The number of incisor teeth is the same as in _Hyrax_, and in these teeth there is also a certain amount of resemblance to the curious genus _Toxodon_, in which the incisors are four in the upper and six in the lower jaw, and worn away in somewhat the same fashion. In _Toxodon_ also, the convexity of the curve of the molars is turned outwards. Certain other characters of _Mesotherium_--such as the mode of articulation of the lower jaw, and the peculiar connection of some of the caudal vertebræ with the ischiatic bones--present resemblances to the Edentata. As Mr. Alston says, “It appears to have been a survivor, to Pliocene times, of a much earlier type, which represented an era at which the Rodents were not yet clearly marked off from their allies. In fact, _Mesotherium_ seems to continue _into_ the order Glires that line of affinity which Professor Flower has pointed out as extending from the typical Ungulates through _Hyracodon_, _Homalodontotherium_, _Nesodon_, and _Toxodon_.” The general relationships of _Mesotherium_ to the other Rodents, and of these among themselves, are represented by Mr. Alston in a diagrammatic form, from which the following scheme, which will serve also as a table of the families, is derived:--