PROFESSOE OWEX OX THE FOSSIL MA:\IMALS OF AUSTEALIA. 



ISO 



of the socket of the third molar (Plate XX. fig. 2, m i) arches inward as it descends, con- 

 tinuing the diastemal transverse concavity to that part of the molar series where the 

 hinder fracture of the present fossil has occui-red, exposing the long curved implanted 

 part of the third molar [m i, fig. 3). 



Another difference is seen at the under part of the symphysis of the fossil (Plate XXIII. 

 fig. 4) as compared with that in the latifront species (ib. fig. 3). In this the longitudinal 

 contour is convex, concurrently with the greater general convexity of the curve of the 

 lower border of the mandible (Plate XXII. fig. 3) ; in the fossil (ib. fig. 7) the lower 

 surface of the symphysis runs straight, or very nearly so, from the hind fracture to 

 the outlets of the incisive alveoli (s'), along a preserved symphysial extent of 2 inches 

 8 lines. It is interesting to see that here, again, the fossil resembles the Platyrhine species 

 (Plate XXII, fig. 2), the older spelaean form combining to a certain extent characters kept 

 apart in still existing species of "Wombat. Nevertheless the more essential resemblances 

 are to the Phascolomys latifrons. The pair of subsymphysial foramina (Plate XXIII. 

 fig. 4, r) characteristic of the "Wombats are wider apart (4 lines) than in the Platyrhine 

 (ib. fig. 1, r) and Tasmauiau (ib. fig. 2, r) species, and show rather the latifront character; 

 they have the usual relative position to the fore and hind ends of the symphysis. 



The specific distinction between the broad-fronted (Plate XXII. fig. 3) and other exist- 

 ing Wombats (ib. figs. 1 & 2) afforded by the ascending ramus of the mandible induced 

 attention to all the cave fragments of that part of the lower jaw, and led to careful 

 removal of the matrix from both the outer and inner depressions. This brought to light 

 the modification of the lower part of the ectocrotaphyte depression [f) shown by the 

 subject of fig. 6, Plate XXII. In the minor depth of the base or lower part of that de- 

 pression the fossil mandibular fragment agrees with Phascolomys latifrons (ib. fig. 3,/'), 

 and more especially with the variety above noted with the absence of the transverse perfo- 

 ration (Plate XXII. fig. 3). The part of the base, or below the base, of the coronoid in 

 the fossil where the canal opens externally in the normal mandibles of Phase, latifrons* 

 is entire ; it is also less depressed there than in the perforate variety. From this and 

 the normal mandible of the latifront species the fossil (Plate XXII. fig. 6) differs in the 

 relative position of the anterior beginning of the '• ectocrotaphyte ridge " [li] or that 

 bounding below the ectocrotaphyte depression (/'). In the three recent species (ib. 

 figs. 1, 2, 3) this ridge (/?) begins near the lower border of the ramus ; in the fossil 

 (ib. fig. 6, h) it begins midway between the lower and upper borders, and on a vertical 

 parallel with the third or antepenultimate molar {in i) — consequently more in advance 

 than in the recent Wombats, in which both the ridge and the base of the coronoid {q) begin 

 below the fore part of the penultimate molar [m -i). Both penultimate and last molars 

 are in place and are worn in the fossil, so the differences above noted cannot relate to 

 nonage. The beginning of the ectocrotaphyte ridge is 10^ lines below the outlet of the 

 first division of the alveolus of ni 2 in Phase, latifrons (ib. fig. 3, h), and is 1 inch below the 

 same part in Phase, jplatyrhiniis (ib. fig. 2, h) ; in the fossil it is 6 lines below the hind 



* Trans. Zool. Soc. vol. iii. plate xxsvii. fig. 5. 



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