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Show 1877.] PROF. OWEN ON A NEW SPECIES OF STHENURUS. 353 nent series of upper molars is 3 inches 4 lines1. In Osphranter rufus this series is 2 inches 3 lines, reduced by loss of the premolar to 2 inches (as in Trans. Zool. Soc. vol. ix. pl. 74. figs. 1 and 3) ; and these dimensions are not exceeded in Macropus major. The extinct Kangaroo, represented by the subjects of Plate X X X V I I . somewhat exceeded the above largest known existing species. The fragment of skull is a little larger than the corresponding part of a full-grown Macropus major, with the last molar in place and use and the premolar shed; it consists of both maxillaries with their respective (right and left) molar series, the intervening bony palate, and a portion of the right orbit and zygoma with the descending masseteric process. The dentition is in an instructive phase. The left series of grinders shows the premolar (ib. fig. 1), p 3, in place, and the last molar, m 3, protruding from the formative cell. The right series shows the deciduous predecessors (d.2, d 3) of p 3 in place, and m 3 less advanced than on the left side. Thus there are five functional grinders on the right side and four on the left side of the upper jaw. The formula ot the left series is p 3, d 4, m 1, m 2 (m 3 not fully emerged) ; the formula of the right series is d2, d%, di, my, mz (mz less advanced). Accordingly the outer parietes of the right maxillary were removed above d 2 and d 3 with the usual result, the crown of p 3 and beginning of its roots becoming exposed in the formative cell (Plate X X X V I I. fig. 2, p 3). The fore-and-aft extent of the left permanent series of upper molars is 2 inches 10 lines, that of the four bilophodont molars (corresponding with those shown in the skull of Osphranter rufus, Trans. Zool. Soc. torn, cit.) is 2 inches 3 lines; but the inferiority of size of the present species of Sthenurus to the two previously known species suggested the "nomen triviale." Sth. minor, however, surpasses in size any known existing Kangaroo, but is the smallest known of its genus. In the comparisons required for taxonomic conclusions as to these large extinct Kangaroos, I found, in 1873, the nearest approach to the character of the premolar of Sthenurus in some small Kangaroos of the genus Halmaturus, and I figured the dentition of H. ualabatus2 (Phil. Trans, torn. cit. plate xxiv. figs. 1, 2, 3, 10, 11, 12) as showing the nearest resemblance to that of S. atlas (ib. ib. figs. 4, 5, 6, 7, 8). But the premolar of the Halmaturus, with the same general type, had less relative antero-posterior extent, and had not the smaller deep-seated transverse ridges ; the bony palate also, as in other Wallabies, presented a pair of large vacuities. Subsequently3 I was enabled to show a more marked generic distinction in the form, sculpturing, and proportions of the upper and outer (third) incisor. In 1874, M . D'Albertis described and figured a small existing kind of Kangaroo under the name of Halmaturus lucluosus*, obtained 1 Phil. Trans. 1874, p. 272, pl. xxvii. figs. 5-9. 2 Lesson, not Gray ; the latter is probably a variety of Halmaturus ruficollis, Desm. 3 Phil. Trans. 1876, p. 211, pl. xxv. figs. 2, 3, pl. xxviii. figs. 1, 3. 4 Proceedings of the Zoological Society, 1874, p. 110, et p. 247, pl. xiii. PROC. ZOOL. Soc-1877, No. XXIII. 23 |