ON DIPROTODON MINOR, HUX. 



39 



a short posterior and a longer anterior talon, the latter armed with 

 a prominent tubercle. By this tubercle seen in profile, and by a 

 mesial indent of the crown, deepening and widening as it approaches 

 the culmen — the tooth is on its outer side made to appear somewha^ 

 trilobate : anteriorly and posteriorly the outer surface is smooth and 

 feebly concave ; the mesial indent is bounded laterally by the free 

 edge of the surface on either side of it, and towards the base by a 

 deep and sharp basal ridge connecting the lateral edges. On its 

 surface of wear it presents a broad stirrup-iron shaped band of 

 dentine, placed transversely with its sole on the outer side. The 

 enamel forming the inner edge of this band is the margin of a 

 subtriangular pit of enamel in the centre of the crown, deepest 

 (about 3 mm ) near the base of the triangle which is opposite the 

 inner side of the tooth, and shallowest at the apex, which is 

 opposite the mesial indent of the outer surface, and separated 

 therefrom by the narrowest part of the linking portion (sole of the 

 stirrup-iron) of the dentinal band. The plan of this surface strongly 

 suggests that at an earlier stage of wear the linking portion was 

 not uncovered and that the dentine appeared as a loop-like band 

 separated at its free ends by continuity of enamel. In this case the 

 tooth at eruption rose as a single lobe, with its summit excavated 

 from the outer side — the excavation forming a transverse valley 

 which sunk deeply into the centre of the crown and passed with a 

 contracted course over the outer edge to join the external indent. 

 The trenchant summit seems to have formed a continuous f] shaped 

 curve of constant breadth ; there is at least no indication in any 

 contraction of the dentinal band that even towards the summit 

 the cusp was subdivided into three parts, one internal and two 

 external. The prebasal or antero-internal ridge springs from the 

 antero-external angle of the tooth, or rather from the tubercle 

 within that angle — it passes inwards, then curves boldly backwards 

 and ascends upon the antero-internal angle ; the postbasal ridge 

 differs mainly in the reversal of its course. The curves of the 

 ridges with the interval between their terminations gives a slight 

 appearance of emargination to the inner side of the crown, and this, 

 in conjunction with the external indent, causes it to appear a little 

 contracted laterally. The prebasal tubercle i> a trian^ar promm- 



