443 



From these materials I have attempted to restore the skull, as in Plate CVIII. 



Of the incisors the first, or foremost (ib. figs. 1, 2, 3, i i), has a greater relative supe- 

 riority of size over the second and third than in any existing species of Kangaroo that 

 has come under my observation ; in this character Sthetiicrus approaches the Koalas and 

 Potoroos among existing, and the colossal Diprotodonts among extinct Marsupials. 



The transverse diameter of the crown of i i is 8 lines (17 millims.); it nearly equals 

 that of the two following incisors, of which the third is broadest, viz. 5 lines (10 millims.) 

 along the oblique trenchant or working border ; the thicker, triturant surface of the 

 second incisor is 4 lines (8 millims.) in longest diameter. The crowns of the six incisors 

 describe a semicircle (ib. fig. 3) ; those of the anterior pair, separated by a line's breadth 

 in the fossil, evidently touched each other in the living animal at their median angles, 

 which show the effects of mutual pressure. 



Each incisor is curved lengthwise with a strong outward or forward convexity ; the 

 exposed enamelled crown of the first measures in a straight line 1 inch 1 line (27 millims.); 

 that of the second incisor 7\ lines (15 millims.) ; that of the third incisor the same : 

 this, as usual, expands to the working-surface ; its outer enamel is bisected by a feeble 

 linear longitudinal groove. The transverse interval between the two incisors of the 

 third pair is 1 inch and a half. The outer half of the fore surface of the crown of the 

 second incisor is prominent, and is pressed into a corresponding channel of the hind 

 surface of the first incisor (ib. fig. 3) ; the channeled part of the contiguous surface of 

 the second incisor reciprocally receives the prominent part of the opposed first incisor. 

 The crown of the third incisor presses closely against that of the second ; thus firmly 

 interlocked, they worked as one tooth. The enamel of the second and third incisors is 

 continued from the outer or fore part of the crown upon part of the hind or inner 

 surface ; but the enamel of the large anterior incisors is limited to the fore part. Thus, 

 in both proportion and structure, the large incisor more resembles, than the other two, 

 the still larger proportional tooth in Nototherium and Diprotodon ; but it still is an 

 incisor of limited growth, and its implanted fang tapers to the end. 



From the back of the medial border of the front incisor (Plate CIX. fig. 10, i i) to the 

 fore border of the ' foramen incisivum ' (ib. a) is 1 inch ; from this border a groove (b) 

 is continued forward, shallowing, to within an inch of the tooth. The breadth across 

 the outsides of the last pair of incisors is 1 inch 11 lines; the breadth of the palatal 

 part of the premaxillaries at the fore part of the prepalatal or incisive foramina is 1 inch 

 9-| lines. From the third incisor to the premolar is 2 inches 1 line ; in other words, 

 this is the extent of the diastema or toothless space (Plate CVIII. fig. 1, d, d') between 

 the incisors and molars. The breadth of the bony palate anterior to the premolars is 

 2 inches 1 line. The length of the molar series (Plate CVIII. fig. \, p 3-m a) is 3 inches 

 6 lines ; in Sthenurus Atlas it is 2 inches 9 lines. The premolar (p 3) exceeds the rest 

 in fore-and-aft diameter, which is, as in the cave-specimen (Plate LXXXVII. fig. 7,p 3), 

 9^ lines (20 millims.) ; the three low transverse ridges which connect the inner with 

 the outer wall are well marked in the present comparatively young though full-grown 



46 



