311 



1 inch 10 lines : the admeasurements are here taken to include the alveolar outlets. In 

 both species there is a slight decrease of size as the teeth recede in position, and chiefly 

 in the hind lobe or division of the last molar ; and in both species the second molar (d 4) 

 is distinguished by the marked increase of size, especially transversely, of the hindmost 

 lobe or division. The apex of the front lobe of the third molar (m l) does not extend 

 so far inward as that of the contiguous lobe of the second molar. The fourth molar 

 (m 2) has a similar relative position to the third ; so that the inner contour of the three 

 mid molars is zig-zag, the palate gaining width between each as they recede in position. 

 This character is better marked in the bare-nosed than in the hairy-nosed Wombat. 

 The outer alveolar wall in all the species is deeper than the inner one, and is nearly on 

 a level with the worn or working surfaces of the teeth. The enamel does not extend 

 upon the outer surface, and thins off before it quite attains the angles between the 

 outer and the fore and hind surfaces (PI. XL VIII. fig. 3, d 4, e ; and PL XLIX. 

 fig. 3, d 4, e). 



The right and left series of the upper molars, as may be inferred from the palatal 

 characters, diverge from the second to the last, in a greater degree in Phascolomys 

 platyrhinus (PI. XLVIII. fig. 1, d 4, m 3) than in Phascolomys latifrons (PI. XLIX. 

 fig. 1, d 4, m 3). 



In a not full-grown latifront Wombat, with a skull 6 inches 2 lines in length, the 

 upper molar series has the same longitudinal extent (1 inch 10 lines) as in a full- 

 grown individual with a skull 6 inches 9 lines in length. The teeth, including the in- 

 cisors, have acquired their full size. This fact bears serviceably on the interpretation 

 of fossil Wombats with markedly smaller molar teeth in upper and lower jaws not 

 exceeding in size those of the young Wombat above compared. 



The lower incisors of Phascolomys latifrons are more distinct in size and shape from 

 those of Phascolomys platyrhinus than are the upper ones. The vertical diameter of 

 the transverse section (as in fig. 2, a, PI. LIV.) is the longest, not the transverse diameter 

 (as in fig. 4, a. ib.). The outer surface, vertical, and slightly channelled, is divided by 

 a well-marked angle from the lower surface, which is slightly and transversely convex. 

 The enamel covering the lower surface bends over the angle dividing it from the outer 

 surface and there stops. In Phascolomys 'platyrhinus the lower enamelled surface bends 

 up upon the outer to near the upper surface, terminating there at an angle or ridge. 

 A narrow longitudinal groove representing the wider outer channel in the hairy-nosed 

 Wombat, divides the enamelled outer angle from the flat upper surface. The transverse 

 section of the incisor may be called triangular in both species ; but the base is internal 

 and the apex external in Phascolomys platyrhinus, while the base is inferior and the 

 apex superior in Phascolomys latifrons. The lower incisors are likewise smaller 

 relatively to the jaw and to the molar teeth in the hairy-nosed than in the bare-nosed 

 Wombat ; and this character is more strongly marked in the large extinct Wombats 

 indicated in my second Memoir on the osteology of the Marsupialia 1 . 



1 Trans. Zool. Soc. vol. iii. (1845), p. 30G. 



