184 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



in the degree usually noticed in comparing upper and lower molars of 

 the same herbivorous animal. The last of the three upper molars 

 shows the surface produced by the pressure of the tooth beyond it ; 

 and its hinder ridge shows the same proportion of minor breadth as 

 in the penultimate molar in the cast of the cranium of Zygomaturus. 



The cingulum forms a ridge along the back part of this molar, of 

 about a line in breadth : the anterior basal ridge is broader, and of 

 greater transverse extent. The enamel on the worn ridges shows 

 the same thickness as in the lower molars of Nototherimn. The long 

 diameter of the crown is 1 inch 10 lines, the cross diameter is 1 inch 

 8 lines. The posterior fang, which is exposed, continues of the 

 same breadth for 2 inches within the socket, without dividing. A 

 Imear indentation divides the fang from the back part of the ena- 

 melled crown. 



The middle (antepenultimate or third) molar (m i) is 1 inch 6 

 lines in long diameter, and nearly the same in cross diameter ; its 

 anterior talon is also thicker than the posterior one. 



The anterior molar (^^4), answering to the second in the lower 

 jaw of Nototherimn, has the two ridges obKterated and worn down to 

 a common field of dentine, with the enamel- wall thickened and en- 

 croaching angularly at the middle of the inner side, where the 

 mid vaUey ended in the younger state of the tooth. This greater 

 degree of attrition of the permanent tooth in advance of the ante- 

 penultimate grinder, is a surer proof of the marsupiality of the great 

 Herbivore than would be the marsupial bones themselves*. 



The molar teeth in the cast of the skull of the Zygomatums 

 present, as ah*eady remarked, the same configuration as the teeth 

 in the fragment of skull above described : the fore and aft extent 

 of the three corresponding teeth in the cast, viz. the second, 

 third, and fourth, is 4 inches 3 lines : their crowns are less abraded. 

 The portion of bony palate preserved in the fragment of the skull 

 shows the same entireness as in the cast of the entire skuU. The 

 three molars exhibit the same slight degree of convex outer, and con- 

 cave inner, contour as do the corresponding molars in the entire series. 



The three molar teeth in the fragment of upper jaw unequivocally 

 belong to the same genus, and almost as clearly to the same species, as 

 do the lower jaw and teeth of Nototherium MitchelU. When the molar 

 teeth in that lower jaw are applied to the molars in the cast of the 

 upper jaw of Zygomaturus, it is difficult to imagine that they have 

 not belonged to the same individual animal, — the correspondence is 

 so close. The indication, slight as it is, of an expansion of the 

 symphysial part of that mandible in advance of the constriction at 

 its beginning in front of the fii'st molar, is most satisfactory, as show- 

 ing the same peculiar feature which distinguishes the short premaxil- 

 lary part of the cranium. 



I conclude, therefore, that the cranium, of which we now possess 

 the cast (Plate YII. figs. 1-4), the fragment of the upper jaw with 

 the molars (Plate IX. figs. 4 and 5), the almost entii'e under jaw 



* The Monotremes have marsupial bones, although no marsupial pouch : the 

 Thylacine has the marsupial pouch, but no marsupial bones. 



