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Show 356 PROF. OWEN ON A N E W SPECIES OF STHENURUS. [Apr. 17, What evidence, it may be asked, does the skeleton afford of the affinities of the huge extinct Kangaroos of the genus Sthenurus 1 I am able only to adduce those yielded by the skull. The time may arrive when, in some Australian cavern, a greater proportion of the enduring framework may be recovered in connexion with the skull and dentition of one and the same individual. Fortunately the cranial characters at present known are instructive ones, are well shown in the portion of skull of the smaller species under description, and the more welcome as repeating those previously given by a corresponding portion of a skull of Sthenurus brehus (Phil. Trans. 1874, plate xxviii. fig. 6). The first of these characters is the integrity of the bony palate. In Dorcopsis (P.Z.S. 1875, plate vii. fig. 2), as in the Hypsiprymninae, and as in most of the smaller Kangaroos which have been grouped under the less-definite genera Halmaturus, Petrogale, Lagorchestes, the bony palate shows two or more large vacuities1. In Dendrolagus the palate is entire, as in Macropus and Sthenurus. The masseteric process is short in Dorcopsis, as in the Hypsiprymnines ; it is long in Sthenurus, as in Macropus. The relative position of the masseteric process to particular molar teeth, outside which it descends, varies at different phases of the acquisition of the molars. In Sthenurus it is always opposite the interspace between the penultimate and last molar " in place." Thus in the immature specimen of Sthenurus minor, in which m 3 is not extricated, the process is opposite the interspace between m 2 and mi; in the mature Sthenurus brehus2 it is opposite the interspace between m 2 and m 3. In the specimen with m 3 in place, but less mature in age3, the process is opposite a larger proportion of m 2, though partly hiding the interspace between it and m 3. The relative position of the masseteric process, described as a differential character between Dorcopsis luctuosa and D. muelleri4, may depend upon the incomplete development of m 3 in the subject of Prof. Garrod's plate vii. fig. 3 (loc. cit.). The forward movement of the molar series is effected by that of their sockets; but the superincumbent pier of the zygoma does not participate in the molecular additions and subtractions to which that movement of the dental cases is due. Such movement is most striking, and was first impressed upon m y mind as the true dynamic in the change of place of growing teeth, in the jaws of the Elephant, 1 The characters of the bony palate are defined and exemplified in the plates of the papers " O n the Osteology of the Marsupialia," in the Trans. Zool. Soc. In vol. ii. pl. lxxi. fig. 5, the vacuities are shown in Halmaturus bennettii (a near ally, if not a local variety of Halm, ruficollis, Gould); in vol. ix. pl. lxxiv. tho entire condition of the palate is shown in Macropus (Osphranter) rufus. 2 ' Eesearches on the Extinct Mammals of Australia,' 4to, 1877, vol. ii. pl. lxxxviii. fig. 6. 3 Ibid. pl. cviii. figs. 1, 21. "In D. luctuosa the apex of the ' angular process which is developed downwards from the inferior margin of the maxillary portion of the zygoma' is opposite the anterior cusp of the third molar tooth, whilst in D. muelleri it corresponds to the posterior cusp of the second molar" (p. 52). In the specimen, as in the ' plate vii.,' the tip of the masseteric process is opposite the interspace optween tbe two lobes of m 1. |