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Show 354 PROF. OWEN ON A N E W SPECIES OF STHENURUS. [Apr. 17, in the south-east of New Guinea, with a premolar more trenchant than in Sthenurus, and with the proportions of the tooth differing in the opposite extreme of fore-and-aft extent, and in greater degree than in Halmaturus, from those of the premolar of Sthenurus. This rare Kangaroo was deposited in the Zoological Gardens, and on its death, in November 1874, was anatomized by the accomplished prosector, A. H. Garrod, B.A., by whom the skull and teeth are well described and figured1.' The state of dentition on both sides of the upper jaw is that shown on the left side of the fossil above described; the premolar is in place, and the last molar partially extricated from its formative alveolus. Prof. Garrod refers the species to the same genus as the Dorcopsis muelleri of Schlegel. The premolar of Dorcopsis luctuosus shows an antero-posterior extent of crown relatively greater than in Sthenurus; it develops a single trenchant ridge, forming the main part of the body and summit of the crown, being supplemented on the outer and inner sides by a subtubercular basal ridge or cingulum. The antero-posterior extent of the premolar in the larger kinds of Sthenurus does not exceed that of the contiguous molar, d 4, and one half of the next molar, m 1; in Sthenurus minor (Plate X X X V I I . fig. 3, p 3) its extent is relatively less; in Dorcopsis it exceeds that of the two succeeding molars and a little over (P. Z. S. 1875, plate vii. figs. 2 and 3). In all the species of Sthenurus the outer ridge of the premolar rises directly from the base of the crown (Plate XXXVIII. figs. 1, 5, 12, p 3), and inclines so little inwards that its summit as well as base is on the outer side of the working surface of the tooth (ib. figs. 3, 7, 14, p 3, d) ; in Dorcopsis there is a series of small prominences, a tuberculate cingulum, on the outer side of the base of the outer ridge, and the trenchant margin of this ridge (through its greater inclination inwards) traverses the middle of the working surface of the tooth2. The tubercular character of tbe inner ridge in Dorcopsis seems a repetition, on that side, of the tubercular cingulum on the outer side of the base of the crown. In Sthenurus the transverse thickness of the premolar decreases as the crown extends forward ; in Dorcopsis the transverse thickness is uniform, or is maintained to very near both ends of the crown (comp. torn. cit. plate vii. fig. 2 with Plate XXXVIII. figs. 3, 7, 14,^ 3). The broadest (hindmost) part of the premolar in Sthenurus (Plate XXXVIII. figs. 7, 14, p 3, c) is not quite equal to that of the fore lobe of the contiguous molar (ib. d 4), and is markedly inferior to that of the next (second) molar (Plate X X X V I I . fig. 1, m 1) ; in Dorcopsis the breadth of the base of the premolar equals that of the next and following molars (d 4). The post-internal tubercle of the premolar of Sthenurus is united by a transverse ridge with the hind summit (Plate XXXVIII. figs. 6, 7, 13, 14, c) of the outer longitudinal lobe or plate (d). The corresponding tubercle in Dorcopsis is not so united with the homo- 1 P. Z. S. 1875, p. 48, pis. vii., viii., ix. 2 Hence Prof. Garrod describes the crown of the tooth as "prismatic in shape," loc. cit. p. 54. |