513 



exaggeration of that of the same part in the premolar of Procoptodon (Plate XC. 

 figs. 2,7,^? 3), of the predecessor of which (d 3) the present tooth in Nototherium is 

 the homologue ; but this tooth (d 3) does not push out any deciduous predecessor in 

 the larger herbivorous bilophodont Marsupials (Nototherium, Diprotodon). 



The anterior lobe (Plate LXXXVIII. figs. 11 & 12, d 3, a) is the smallest and shortest ; 

 the enamel of its obtuse summit is polished by wear, but no dentine is exposed. A 

 fold of enamel (/) detaches itself from the fore part of its base and curves backward 

 and inward to rise again and subside near the summit of the inner lobe (d) of the tooth. 

 This fold of enamel, which may be termed a " prebasal " one, is sinuous in its course. 

 The mid lobe (b), rather broader than the fore one, has its summit worn down, and a 

 flat field of dentine, with a border of enamel, is exposed (fig. 12), the contracted inner 

 part of which border is continuous with the apex of a similarly worn surface of the 

 inner lobe (d). The hinder (c) of the three outer lobes is the largest, chiefly through 

 the expansion and backward extension of the base. The exposed dentine on its worn 

 summit is continued inward with its enamel border to that of the inner lobe, which 

 thus seems to be a production of the third lobe. The cleft between the middle and 

 hinder of the outer lobes expands as it passes inward, and the inner lobe (d) bends 

 round the expansion to be continued into both middle and hinder lobes. The hind 

 surface of this milk-molar (ib. fig. 14) is less broad than either the inner or outer sides of 

 the tooth ; it is fiat, slopes from below forward, and is bounded by a thick, but narrow 

 postbasal ridge (g), which gradually subsides as its extremities pass vertically to the 

 outer and inner summits of the posterior lobe. 



The enamel of the flat sloping surface shows fine vertical grooves and punctations 

 where it is not worn. The crown of the tooth, in the present worn state, is broader 

 from before backward than it is high. The transverse basal breadth and the exterior 

 height of the unworn crown are the same. It is supported by two roots, the hindmost 

 being the largest. The length of the crown is 1 inch Inline (29 millims.); the 

 greatest breadth is 10 lines (21 millims.). 



In Nototherium Viccorice (Plate LXXXVIII. figs. 15-17) the three outer lobes of the 

 milk-molar are represented by as many vertical angular ridges (ib. fig. 15, d s,a,b,c) 

 with wide transversely concave or angular intervals, bounded below by curved lines, the 

 hinder one formed by a bulging ridge (fig. 15, e). The anterior lobe (a) seems to be 

 rather an angular ridge forming the fore part of the crown; its hind border (fig. 16,/) 

 extends inward and backward, rising at an acute angle and thickening to terminate on 

 the hinder apex (d) of the back surface of the crown. The mid external lobe (fig. 15, h) 

 has a flat field of dentine exposed, shaped as in Nototherium Mitchelli, and is continuous 

 by its apical part with the inner lobe. The outer and hinder lobe (c) is chiefly repre- 

 sented by the enamel covering its outer surface. The hinder surface (ib. fig. 17), 

 bounded below by the postbasal ridge (g), slopes to terminate in the ridge of enamel 

 continued from the apex of the postexternal lobe (c) across the summit of the crown 

 to d. The length of the crown is 1 inch, the breadth is 9^ lines (20 millims.). 



