1862.] HUXLEY — DIPROTODON. 425 



narrower from the level of the commencement of the third molar ; so 

 that, no doubt, a great palatine vacuity existed at this spot. This 

 is the more remarkable, as, judging from a cast in the same col- 

 lection, the palate of Nototherium vras entire, and extended, as in the 

 Kangaroos, behind the last molar tooth. 



The molar teeth have the general characters of those of the lower 

 jaw of Biprotodon already described by Professor Owen. Each 

 exhibits two principal transverse ridges, with a posterior, almost 

 obsolete, and an anterior, much more prominent and thick, but still 

 low, basal ridge. The principal ridges are directed transversely to the 

 axis of the palate and the alveolar margin, or have, at most, but a very 

 slight inclination backwards and inwards. They are slightly concave 

 backwards ; and they wear down at first into two oval or elongate - 

 reniform facets, separated by a deep valley, whose outer ends are, 

 as usual, higher than the inner. The tooth becomes abraded faster 

 in front than behind, — the anterior basal ridge contributing a single 

 or double strip -like facet, which becomes connected in the middle 

 with the worn face of the anterior of the two principal ridges. The 

 latter also eventually unite in the middle of the tooth ; so that, in 

 much- worn teeth, the broad, four-sided field of dentine is surrounded 

 only by a narrow band of enamel, the lateral portions of which present 

 two sharply re-entering angles. There is no cingulum continued upon 

 either the outer or the inner sides of the base of these teeth. The sur- 

 face of the enamel has that sort of " reticulo-punctate or worm- 

 eaten " look which is mentioned by Professor Owen as characteristic 

 of the teeth in this genus. 



The first molar is rather smaller than the second : the third is 

 wanting : the fourth is considerably longer than the second, as the 

 measurements given below will show, and has not the square out- 

 line of the first and second ; but it diminishes posteriorly by the 

 incurvation of its outer contour. Hence the posterior transverse 

 ridge of the fourth molar is much smaller than the anterior. The 

 tooth is not at all worn, and seems to have been but just cut. The 

 principal crests are excavated from side to side posteriorly, and are 

 correspondingly convex anteriorly. Superiorly they rise to a minutely 

 ridged and forwardly curved edge, which is slightly concave up- 

 wards. The anterior basal ridge is sharply defined, but is not so 

 thick as in the second molar. 



Each molar tooth has a single posterior fang and two anterior fangs. 



The premolar tooth (not more than half the size of the molar 

 which succeeds it, and very much less worn) differs somewhat in its 

 characters in the two fossils. I wiU first describe it as it appears 

 in No. 1, where the premolar teeth of both sides are preserved. 

 The tooth is implanted by two fangs, an anterior, smaller, and a 

 posterior, larger ; and its crovni has somewhat the form of a tetra- 

 hedron with a truncated apex. The posterior side is flat, and slopes 

 obliquely forwards to the roof-like summit of the tooth. The outer 

 convex surface (fig. 1) is divided into three minor vertical convex- 

 ities by two shallow grooves, which cease about halfway towards the 

 base of the crown. The inner surface (fig. 3), less extensive than the 



