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Show 1877.] PROF. OWEN ON A NEW SPECIES OF STHENURUS. 359 course. The condition of di in the Kangaroo adds to the characters which have led odontologists to regard the three "true molars " of the diphyodont mammals, as being essentially a backward continuation of the first or deciduous series of teeth. With respect to d2, in Macropus, F. Cuvier remarks1:-" Dans le jeune age, la premiere macheliere est mince et analogue aux fausses molaires des genres precedens" (Halmaturus, Hypsiprymnus). "A mesure que les dents posterieures se developpent, les anterieures qui sont usees et qui sont poussees en avant par les premieres, s'obliterent et tom-bent de maniere qu'elles finissent par se reduire a trois. Ainsi les premieres ne sont pas, comme chez les halmatures, remplacees par des dents qui se developpent sous elles, mais par les dents qui se sont developpees derriere elles." Now, if this statement of the distinguished odontologist (to whom we are indebted for the first work containing figures and formulae of the teeth of the class Mammalia as then known) had been founded on fact, the distinction of Sthenurus from Macropus and its concomitant resemblance to Dorcopsis would have been as great as Prot. Garrod seems to have concluded. The mistake may have arisen from F. Cuvier having limited his quest to the part of the jaw immediately beneath the slender ' premiere macheliere' (d,2, B, in fig. 1). But had he carried the investigation further back he would certainly have come upon the vertical successor, p 3, of d z, which he so well describes as characterizing his (not Uliger's) genus Halmaturus-. This procedure I practised in comparing, for description in the 'Appendix' to Mitchell's 'Three Expeditions' &c, the fossil remains from Australia, which that early and distinguished explorer of the continent brought to England and submitted to me in 1836; and thus I became aware of F. Cuvier's mistaken view of the generic character of Macropus, and was led to the discovery of the immaturity of the individual Macropodidae of which portions ot the fossil mandible and teeth seemed to represent full-grown Kangaroos o larger size than the largest known living specimen, called on that account Macropus major. Later investigations of the fossil marsupials of Australia have led to the interesting result, that the developmental condition which F Cuvier believed to differentiate the larger Kangaroos of the genus Macropus from the smaller kinds referred to Halmaturus and Hypsiprymnus does actually differentiate the huge extinct herbivorous marsupials of the genera Nototherium and Diprotodon from the MacropodidU which we now know to have been represented by Species much exceeding in size the existing Kangaroos. Moreover, he large extinct Kangaroos, even in the partial degree in which we have already come to know them, manifest much better grounds Tr generic or subgeneric distribution than do any of the existing form?. And such extinct genera, represented as they are by species I TcST^. ^S^^i^ iH-tratio- of the deci-duou^ nf permanent premolars of Hypsipr^nusn plate x. figs. 2, 4, of his 'Natural History of the Mammalia, 8vo, 1845, p. un. |