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Show 360 PROF. O W E N ON A N E W SPECIES OF STHENURUS. [Apr. 17, larger than the existing kinds, manifest in a highly interesting and suggestive way an approximation to the Notothere and Diprotodons. In Nototherium, although the premolar (by position) is characterized by an outer and an inner plate, antero-posteriorly disposed1; yet the transverse breadth of the tooth is proportionally so much greater than the fore-and-aft length, and the connecting ridges of the two plates, through the folding of the inner one, are so large, that the hind part of the premolar already assumes the character of a lobe of the transversely ridged dilophodont molars. In Diprotodon the dilophodont character is better shown2, and the premolar (by position) is the first of the series of such molars, differing only in its inferiority of size. The qualification "by position" means that the tooth is not a veritable premolar, it never displaced vertically a de-: ciduous predecessor, either in Nototherium or Diprotodon, but is the homologue of d z in the Pig and Kangaroo. Macropus, Sthenurus, Procoptodon exemplify stages of transition to the exclusively vegetarian character of the molar series exemplified by Diprotodon. The genera Halmaturus, Dorcopsis, Dendrolagus, Hypsiprymnus exemplify as many stages in the modification of the teeth for a mixed diet, which, in the Diprotodont series of Marsupialia, culminated carnivorously in Thylacoleo. Here the upper anterior incisors, i 1, acquired their largest proportional size with the change of the trenchant for the piercing or laniary type. The single lower pair of incisors underwent the same modifications. The conversion of the premolar, in size and shape, to a carnassial tooth, and the reduction of the molars in number and size to the tubercular condition of the feline molar, are exemplified, in Thylacoleo, with corresponding figures of the jaws and teeth of our Cave-Lion and Cave-Hyaena, in plate vi. of m y ' Researches on the Fossil Mammals of Australia.' In this work a preliminary chapter is devoted to the extinct Marsupials of England, in which it is shown that, at the oolitic period, our Marsupials had also diverged, by modifications of tbe fundamental type, into species exemplifying the ' polyprotodont'3 and the 'diprotodont'4 suborders - and that, in the formal or adaptive characters of the teeth, species diverged from the common carnivorous or insectivorous types exemplified in Stylodon5 and Thylucotherium6, to the vegetarian type in Bolodon7 and Stereoyna-thus* in one direction, and to the carnivorous type exemplified by Triconodon and Plagiautax, in the opposite route. EXPLANATION OF THE PLATES. PLATE XXXVII. Sthenurus minor, O w. Fig. 1. Palatal surface of skull with right and loft molar series. 2. Outer side view of alveolar part of the right maxillary, with the molar series in situ, and the undeveloped premolar exposed in its formative cell. 1 ' Researches,' &c. vol. ii. pl. lxxxviii. figs. 11-16. 2 Ibid. pl. cxxiv, cl 3. 3 Ibid. pl. ii. fig. 17. 4 Ibid. pl. iv. fig. 16. s Ibid. pl. ii. fig. 14. « Ibid. pl. i. fig. 23. 7 Ibid. pl. iii. fig. 5. » Ibid. pl. iv figs. 9-15. |