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Show 494 MR. R. LYDEKKER ON SCELIDOTHERIUM. [Nov. 16, The only other part of the skeleton to which I wish to call attention is the astragalus, and I have accordingly figured the type specimen in Plate XLIX. fig. 3. It will be seen from this figure that the external trochlear ridge for articulation with the tibia is not prominent, and scarcely projects above the level of the internal tuberosity. The astragalus (B.M. No. 37476) associated with the cranium No. 37308 exhibits precisely similar features, although it is of somewhat larger dimensions. This type of astragalus is very widely different from that of Megatherium (in which the external trochlear ridge is extremely prominent), and apparently indicates that the eversion of the foot was not so great as in that genus. SCELIDOTHERIUM BRAVARDI, n. sp. This species is founded on an imperfect skeleton in the British Museum, brought by Bravard from the Argentine Republic, which presents features clearly showing that it cannot belong to the type species, to which it has hitherto been referred. The cranium (B.M. No. 37626), which lacks the whole of the dentition and the greater portion of the nasals, has been figured by Sir R. Owen in the ' Philosophical Transactions' for 1857, pi. viii. fig. 2, from the palatal aspect1, and referred to the type species; an upper view is given in Plate XLVII. of the present memoir. It is extremely unfortunate that the nasals are wanting; but from the structure of the adjacent bones it can be shown that these bones were certainly much shorter than in S. leptocephalum, since in the first place the superior border of the facial portion of the maxilla forms a much shorter curve than in the latter, while if the nasals were of the same length as in that species they would have projected far in advance of the premaxillse. That the nasals were of a shorter type is also evident from a comparison of the figure with that of S. chiliense (Plate X L VIIL), when it will be seen that the facial portion of the maxilla is not dissimilar in the two species. The whole cranium is, moreover, relatively narrower than in S. leptocephalum, and the frontal profile is quite straight; while only a narrow moiety of the facial portion of the maxilla appears on the frontal aspect; and the lachrymal is characterized by its extreme prominence, and the partially upward direction of the aperture of its canal. The anterior border of the zygomatic process of the maxilla is nearly vertical, while the fronto-parietal ridges are closely approximated, and the interdental portion of the palate (as is well shown in Sir R. Owen's figure) is of excessive narrowness. It will also be seen from the following table of dimensions that while the width of the occipital condyles is smaller than in S. leptocephalum, the interval between the condyles and the last tooth is considerably greater, which indicates a great difference in the relative proportions of the two crania. The premaxillae are well developed. In the mandible2 associated with the cranium, while the length of 1 The teeth have been introduced on one side in this figure. 2 This specimen is figured by Owen, op. cit. pi. viii. figs. 4, 5, with the teeth restored; and apparently in pi. ix. figs. 2, 3, the specimen represented in fig. 2 being erroneously described as belonging to the upper jaw. |
