440 



a Larger molar is preserved behind that tooth. This evidence of immaturity is supported 

 by the incomplete exclusion of the crown of the third incisor (ib. ib. i 3 ); and the corre- 

 al tondence of the stage of dentition with the second (B) of the series m Macropus major, 

 figured in my ' Anatomy of Vertebrates'*, was demonstrated by the usual test, viz. the 

 exposure of the crown of the replacing tooth (p 3) in its formative alveolus, above the 

 deciduous teeth (d a, d 3) in place and use (Plate LXXVII. fig. 4). The third bilo- 

 phodont tooth (m 1) on the left side is not so far advanced as its homologue in the jaw 

 showing the third stage (op. cit. ib. C) of the dentition of the Macropus major. The 

 germ of the premolar and the deciduous teeth in place accord with the characters shown 

 in more fragmentary specimens of Sthenurns Atlas. Consequently can be added, by means 

 of the present fossil, the characters of the first and third upper incisors to the previous 

 knowledge of the dentition of that large extinct species. 



The present portion of a young individual of Sthenurus Atlas presents a condition 

 which significantly points to the nature of its violent death, and to the operation of the 

 powerful jaws and teeth of its carnivorous destroyer. 



The upper jaw, anterior to the orbits, has been nipped in by a cross-bite ; another 

 grip in a vertical or obliquely vertical direction in the orbital region has crushed the 

 right half in the course of the interfrontal and internasal sutures, to a lower level than 

 the left half, with a similar degree of forward dislocation. The skull has been subject 

 to this violence in its fresh state, and the matrix has subsequently become petrified 

 about it, and has preserved the dislocations. If they had been due to movements of the 

 matrix after fossilization, the petrified bed would show fracture corresponding to the 

 bone ; but no such evidence of posthumous crushing of matrix and fossil being present, 

 I presume that the skull, if it had been imbedded, uninjured, would have retained its 

 form when petrified, and conclude that the actual state of the fossil was that in which 

 it was interred before petrifaction began. 



The anterior incisor (Plate LXXVI. fig. 2, i 1, Plate LXXVII. fig. 4, i 1) is curved, 

 as in most existing Kangaroos ; but besides its superiority of size to that in the largest 

 kind as shown by the breadth of the crown (Macropus major, e. g. Plate LXXX. fig. 17, 

 Macropus rufus, Plate LXVL), the exserted and enamelled portion is both absolutely 

 and relatively longer, and thus makes a nearer approach to the character of the first 

 upper incisor in Liprotodon (Plate XIX. i 1). 



The convex or fore surface of the crown of i 1 in Sthenurus Atlas is traversed longi- 

 tudinally by a shallow and rather wide groove behind the mid line of that surface, which 

 groove deepens near the cutting edge, and thus marks it with a feeble notch. The 

 1'iiamel also shows some fine longitudinal striations. The enamel is uninterrupted, but 

 becomes much thinner at the back part of the tooth. A transverse section of the crown 

 would give a long narrow oval, rather broader at the outer and hinder end. 



The breadth of the tooth, or length of the oval, is 10 millims. or 4| lines ; the thick- 

 ness or antero-posterior extent is 4 millims. or 2| lines. The hind margin of the tooth, 



* 8vo.. 1868, vol. iii. p. 380, fig. 296. 



