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Show 174 DR. A. S. WOODWARD ON EXTINCT [Mar. 5, anterior margin, but is nearly complete at its overlapping hinder border. It evidently consists of three pairs of scutes firmly fused together, their lines of uuion on the outer face being marked by slight longitudinal grooves. As seeniu end view (fig. 2), the ring is only very slightly wider than deep, and its form is rather hexagonal than cylindrical. The lower pair of scutes constitutes the flattened base of the ring, and curves upwards on either side to form the lower margin- of the lateral face. Each of the lateral pairs of scutes tapers backwards into a blunt triangular prominence, which reaches very slightly beyond its hinder, overlapping facette. The upper scutes, forming the roof of the ring, are produced backwards aud upwards into a divergent pair of autero-posteriorly compressed, pyramidal bosses, which project considerably above and behind their overlapping facette. Externally (fig. 2 a), all these scutes are quite smooth; internally, they do uot exhibit any trace of contact or connection with the endoskeleton. As already mentioned, the microscopic structure of the bony tissue seems to have been destroyed. Part of a second caudal ring, of similar type, was discovered along with the imperfect skeleton in 1899. Generic and Specific Determination. If the South American fossil skull aud maudible now described be compared with the corresponding parts of the type species of Miolania, M. platyceps, from Lord Howe's Island, a remarkable resemblance in all essential features is observable. The skull of M. platyceps is nearly similar in shape, with its temporal fossa? completely roofed by bone, and its external contour modified by the fusion of dermal, bony bosses with several of its elements. It exhibits the same broad plate of bone on the cheek behind the tympanic cavity, a precisely similar palate, and the complete lamiuar septum between the nasal chamber and the orbit. Moreover, the nasal bones in M. platyceps scarcely project farther forwards than the premaxillae. Several minor differences, however, may be noted. In M. platyceps all the bosses are relatively much smaller than in the new fossil. The occipital pair are two well-separated small thick bosses, apparently solid and connected with the postero-lateral " horns," The latter are ovoid or rounded iu section, turned upwards as much as outwards, and considerably smaller in two of the specimens described and figured by O w e n ' than in a third specimen 2, which has also been described by Huxley under the name of Ceratochelys sthenurus*. Except the interparietal, all the bosses seen iu the South American specimen also appear to have slight representatives in M.platyceps ; but the latter exhibits an additional small prominence antero-iuferiorly at the 1 Phil. Trans. 1888 B, pis. xxxi.-xxxiv. 2 Phil. Trans. 1886, pi. xxx. 3 T. H. Huxley, " Preliminary Note on the Fossil Remains of a Chelonian "Rpmtil'e Ceratochelus sthenurus, from Lord Howe's Island, Australia," Proc. Roy. Soc. vol. xiii. (1887), pp. 232-238. |