536 



PEOrESSOE OWEN ON THE FOSSIL MAMMALS OF AIJSTEALIA. 



surfaces of which present the deep and wide longitudinal groove, as in the Tapir, Dino- 

 there, and Kangaroo, are connected together at their base by a ridge coated thickly with 

 cement, and extending longitudinally between the beginnings of the opposite grooves in 

 Biprotodon. 



The third molar in the young specimen (Plate XLI, figs. 1 & 2, m 1) has both lobes par- 

 tially abraded; the fore-and-aft extent of the tooth is 1 inch 10 lines, the basal breadth 

 of both lobes is the same, viz. 1 inch 1-| line. The reticulo-punctate or "worm-eaten" 

 character is strongly marked on the enamel of the fore part of the front lobe ; this is 

 slightly concave transversely at its upper part, the outer and inner borders inclining 

 forward to receive the upward continuations from those ends of the anterior transverse 

 ridge (/). The middle of the hind surface of the front lobe (Plate XL. fig. 7, a) is pro- 

 minent, making the masticatory surface widest at that part. The prominence {b) from 

 the opposite surface of the hind lobe looks more like an infolding of the outer border 

 of that lobe, a character exaggerated in most Kangaroos ; the inner border of the hind 

 lobe is slightly produced backward as well as forward. The hind surface of the hind 

 lobe does not show the mid prominence. The hind transverse basal ridge [g) is highest 

 and thickest at its middle ; the ends of this ridge are less distinctly continued upon the 

 corresponding borders of the hind lobe than in m 2. Ihe slight backward curve of the 

 lobes appears in the profile view of m 1, fig. 6. 



In the older jaw the lobes of m 1 (Plate XL. fig. 9) are worn down nearly to their 

 bases. The front transverse ridge rises a little above the hind one of the antecedent 

 tooth; about 5 lines extent of the fore part of the front lobe rises above the ridge. 

 The anterior enamel-line of the worn surface is nearly straight, the posterior one 

 forms a low angle answering to the prominence of that surface of the lobe. The 

 valley between the two lobes is most shallow and narrow at its middle. The abraded 

 surface of the hind lobe is transversely elliptical, 1 inch 4^ lines in transverse dia- 

 meter, and 8 lines in the opposite diameter ; its hind border is worn down within 3 lines 

 of the posterior basal ridge {g), which abuts against the next tooth above its anterior 

 ridge. 



The fourth molar {m 2) in the younger specimen (Plate XL. figs. 9 & 10) has a line of 

 dentine exposed on the summit of the front lobe (a), but the enamel is not worn off that 

 of the hind lobe [b). The transverse concavity of the fore part of the front lobe is well 

 marked at the present early stage of attrition : the convexity of the back part increases 

 towards the base of the mid prominence. The ends of the front basal ridge (/) rise a 

 little way upon the outer and inner borders of the front lobe. The transverse concavity 

 of the fore part of the hind lobe is narrowed, as it descends, by the reciprocal and pro- 

 gi-essive inbending of the outer and inner borders of the lobe upon the front surface, as 

 this approaches the base of the lobe. The height of the hind lobe from the middle of 

 the valley is 1 inch 3 lines ; the antero-posterior extent of the middle of the base of the 

 lobe is 10 lines. The posterior basal ridge [g) resembles that of m 1, bearing the same 

 proportion to the front ridge. 



