PEOFESSOE OWEN ON THE EOSSIL MAMMALS OF AUSTEALIA. 



253 



ectocrotaphyte cavity preserved in the present cast indicates the same depth ; the 

 symphysial articuhir surface (Plate XL. fig. 1,5,6') has the same shape and extent; the 

 molar teeth (ib. fig. 1, d 3, d 4, 7)11,2,3) show the same configurations and proportions of 

 their grinding-surface (Plate XXXVI. fig. 4) — the extent of the series is 4 inches 7 lines. 

 The length of the incisor (Plate XL. figs. 1, 'i, & 2) is 7 inches, its vertical diameter is 

 8 lines, its transverse diameter 6 lines. The section of the tooth (ib. fig. 4) is lozenge- 

 shaped, with the four angles rounded. The lateral angles (e, e') are nearer the upper 

 (u) than the lower (0) angles, and the lower inner facet (g) is broader than the lower 

 outer one (h) ; the convergence of the two broad lower facets to the obtuse lower 

 angle makes that part of the incisor the narrowest or smallest : if the angles were 

 rounded off, the shape of the transverse section would be an oval with the large end 

 upward. The upper and inner angles are less rounded and more marked than the outer 

 and lower angles. Two low narrow ridges traverse lengthwise the inner and lower facet 

 (ib. fig. 1, ff, g), dividing it into three tracts, the lowest being the narrowest; the outer 

 and lower facet (ib. fig. 2, h, h) is slightly hollowed. A thin layer of enamel coats the 

 lower and lateral parts of the tooth up to the lateral angles (e, e'), where it subsides 

 abruptly after becoming thinner than it was below. 



The base of the incisor in the left ramus of the first-described jaw of Phase olomys 

 gigas (Plate XXXVI. figs. 1 & 2, 'i, and Plate XXXVII. fig. 2,z) repeats the characters 

 above given from the cast of the entire incisor, the original of which is in the Australian 

 Museum ; the outer lateral angle is more sharply marked at the implanted part of the 

 incisor compared. 



The contrast in the shape and relative size of the incisor of the giant Wombat with 

 that of the largest known living species {Phascolomys ;platyrMnus) is great. The section 

 of the incisor in that species has an area double that of the section of the first molar ; in 

 Phascolomys gigas these proportions are almost reversed. The long diameter of such 

 section of the incisor is transverse in Phascolomys platyrhinus ; it is vertical in Phasco- 

 lomys gigas. Amongst living Wombats an approach to the extinct giant is made 

 by the Phascolomys latifrons, in which the vertical diameter prevails in the section of 

 the incisor — only the large end of the oval, or base of the triangle, is below, not above as 

 in Phascolomys gigas ; and the area of the section in Phase, latifrons rather exceeds that 

 of the anterior molar, d 3. In the extinct Phascolomys medius (Plate XXXIV. fig. 4, i) 

 we have a nearer approach to the characters of the lower incisors in Phascolomys gigas. 



Another evidence of Phascolomys gigas is the hind part of the right mandibular ramus 

 with a more mutilated "ascending branch" than in the subject of Plate XXXVI. ; it 

 includes the sockets of the last four molars and the base of that of the incisor. The 

 teeth in this specimen must have presented the size of those in the subject of fig. 4 (ib.) ; 

 the longitudinal extent of the last three sockets is 2 inches 10 lines. The hind fracture 

 is at the intercommunicating canal (Plate XXXVII. fig. 4, p), exposing the wide 

 beginning of the dental canal (ib. 0), with its larger division continued along the outer 

 side of the bases of the molar alveoli, and the smaller division (0') extending along the 



