PROFESSOR OWm ON THE FOSSIL MAMMALS OF AUSTRALIA. 



535 



backward, broader transversely, than that of the front lobe. A low and short ridge of 

 enamel (A) closes both outer and inner ends of the intervening transverse valley. The 

 length or vertical extent of crown between the end of the valley and the division into 

 fangs is 5 lines on the inner side and 4 lines on the outer side of the tooth. The middle 

 of the hind surface of the hind lobe swells out ; and as both outer and inner ends of the 

 hind basal ridge (g) bend up the corresponding parts of the hind lobe, its hind surface 

 shows two shallow depressions divided by the above-named rising : in these depressions 

 the reticulo-punctate character of the enamel is most strongly marked. The hind basal 

 ridge is thicker than the front one (f), and thickest at its middle ; its enamelled margin 

 is irregular, it rises higher than, and seems to overlap, the front basal ridge of the fol. 

 lowing tooth. The cement upon the exposed part of the crown of d 4, between its ena- 

 melled lobes and implanted fangs, is thick. The fangs are two in number, broadest 

 transversely, slightly divergent, canaliculate on the contiguous sides. 



In the jaw of an older Dijorotodon the second molar (Plate XL. fig. 4, d 4) shows both 

 lobes abraded to their common base, exposing the osteo-dentine (o) obliterating the 

 cavity of the fang. A small part of the enamel of the front basal ridge (f) shows its 

 position as blended with the front lobe. The line of enamel of the worn hind surface 

 of the hind lobe (b) forms an open angle, of which the apex shows the end of the pro- 

 minence joining the middle of the hind basal ridge (g), and dividing the remnants of 

 the pair of depressions between that ridge and the hind lobe. The fore-and-aft extent 

 of the worn surface of this molar is 1 inch 6^ lines ; that of the base of the crown is 

 1 inch 8 lines ; the breadth of the hind part of the worn surface is 1 inch. The alveolar 

 border rises into an angle between the origins of the fangs. 



In Plate XL. fig. 2 shows the working-surface of the crown of d 4, of rather smaller 

 size than those above described, and probably from a young female Di^rotodon. The 

 summit of the anterior lobe is so far worn as to expose a transverse curved line of 

 dentine, concave forward, beginning to expand where attrition has reached the promi- 

 nent part of the hind surface of the lobe. The summit of the posterior lobe (b) has 

 just been touched. The proportions of the basal ridges (f, g) are well shown. The 

 reticulo-punctate character of the enamel is well marked. This tooth was from the 

 freshwater deposits of the Province of Victoria, near Melbourne. The outer side view 

 of this tooth is given in figure 1. 



From the same locality I received the third molar (ml) of the same Biprotodon 

 (Plate XL. figs. 5 & 6) : its almost untouched lobes are more compressed than in the Tapir 

 and Dinothere, and their lamelliform summits rise higher beyond their basal connexions 

 than in the Kangaroo ; the median connecting ridge which extends between the two 

 transverse eminences longitudinally, or in the axis of the jaw in the molars of the 

 Kangaroo (ib. fig. 14), is very feebly indicated by the outswelling, shown in figs. 

 3 & 7, at the back of lobe «, in the Biprotodon. The anteriorly concave curve of the 

 summits of the transverse lobes, in fig. 6, is more regular, equable, and greater than 

 in the Tapir (fig. 15), the Dinothere, or the Kangaroo. The two fangs, the contiguous 



MDCCCLXX. 4 D 



