PEOFESSOE OWEX OX THE FOSSIL MAMMALS OF AUSTEALIA. 



251 



that feature of the mandible of the Megathere, and it has a like relation to the 

 lodgement of the formative matrices of long, ever-growing molars *. 



The first molar (ib. figs. lSco,(1 3) is subbilobed, through opposite longitudinal shallow 

 grooves equally dividing the tooth. The tendency to a gain of grinding- surface in the 

 direction of the jaw's axis seen in the same tooth of Phascolomys medius is in the larger 

 species carried further, so as to substitute for the representative of one half or lobe of 

 the succeeding molars in the anterior one of smaller "Wombats a moi-e simplified con- 

 dition of the normal bilobed phascolomydian type of molar. The enamel of d 3 in 

 I^hascolomys gigas is continued from the outer over the front side, and along nearly the 

 whole of the hind side of the tooth. A coat of cement of similar thickness covers the 

 inner side, and is continued more thinly upon the enamel. The surface of the enamel 

 is longitudinally rugoso-striate. 



All the succeeding molars have a partial coat of enamel, extending from the outer 

 side upon the fore part to where this comes into contact with the antecedent tooth, and 

 continued, perhaps, a little further upon the hind surface. The rest of the dentine has 

 the coating of cement. The proportions of the several teeth are shown in the figures 

 above cited. 



As before remarked, the smaller size of the last molar indicates the Latifront Wombat 

 to be nearer akin to the. extinct giant than are the bare-nosed living species. The 

 same affinity is shown by the small size of the lower incisors in Pliascolomys gigax 

 (Plate XL. figs. 1, i', 2, 3, 4). They are smaller, especially narrower, in Phascolomjjs 

 latifi'ons than in Phase, jilatyrliinus and Phase, vombatus, and are, relatively, still 

 smaller in Phase, gigas, with a distinctive shape. But the characters of the lower pair 

 of incisors are better shown in another mandibular specimen of the present large species. 



The section or transverse fracture of the hollow base of the right incisor is shown in 

 Plate XXXVII. fig. 2, i ; the length and curvature of the implanted part of the second 

 molar (d 4) are seen in the same figure, in which e e indicates the anterior terminal line 

 of the outer enamel. The hinder fracture of the left ramus of the same jaw (ib. fig. .3) 

 shows the length and curve of the penultimate molar [m 2), and the posterior terminal 

 line of its partial covering of enamel [e). 



Of the above-described instructive specimen of Phascolomys gigas little more than an 

 inch of the diastemal part of the jaw is preserved (Plate XXXYI. figs. 1 & 2, 1). Fortu 

 nately, the first specimen which made known to me the fact of so large a "Wombat having 

 formerly existed in Australia included 2 inches 8 lines of the diastemal part of the jaw, 

 which contracts rapidly to the terminal outlets of the incisive alveoli (Plate XXXIX. 

 iigs. 1 & 2) ; whence I conclude that but little had been broken away from that end of 

 the mandible. 



* ShoTild an}' successor deem the differential characters of the giant Vomhat of generic or subgeneric value, 

 as the minor differences of Phascolomys latifrons have been by Dr. Mueie (Proc. Zool. Soc. 1S67, p. 815), they 

 may, perhaps, accept the name ' Phascohnus,' having reference to the size of this species, which equalled that 

 of the Wild Ass. 



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