356 PROFESSOR OWEN ON THE SPECIES OF PHASCOLOMYS. 



In Phascolomys latifrons the worn surface of the first upper molar (PI. LIII. figs. 1 

 & fig. 3, d 3) is subquadrate ; or, if viewed as triangular, the antero-internal surface 

 forms the base, and the postero-extemal angle the obtusely truncated apex. There is 

 a feeble indication of a longitudinal groove, representing that in Phascolomys platy- 

 rhinus (PI. LII. fig. 3, g) ; but it does not mark off an anterior production of the tooth 

 in the bare-nosed species, it simply indents the base or shorter side of the triangle. 

 The enamel extends from the base upon the fore and outer part (PL LIII. fig 3, e) 

 and upon the hind part of the tooth, leaving about the same extent of the outer and 

 hinder part unenamelled and coated with cement {c) as in Phascolomys platyrhinus. 

 The chief distinction is the deeper antero-internal longitudinal groove (PI. LII. fig. 3, g) 

 marking off a more definite anterior angle or lobule of the grinding surface of (Z 3 in 

 both the bare-nosed Wombats ; by which character a detached tooth might be deter- 

 mined as not belonging to the haiiy-nosed species. There is only some difference in size 

 between d 3, upper jaw, of Phascolomys platyrkinus and that of Phascolomys vomhatus. 



The second molar {d i) assumes a greater proportional size to the fii-st {d 3) in Phas- 

 colomys platyrhinus than in Phascolomys latifrons ; and the succeeding molars repeat the 

 same degree of superiority of size. The longitudinal extent of the upper molar series in 

 Phascolomys platyrhinus averages 2 inches 1 line; in Phascolomys latifrons it averages 

 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 i) 

 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 i) 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. LII. fig. 3, di, e; and PI. LIII. fig. 3, d 4, e). 



The right and left series of the upper molars, as may be inferred fi-om the palatal 

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

 tyrhinus (PL LII. fig. \, d i,m 3) than in Phascolomys latifrons (PL LIII. 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 ia length. The teeth, including the in- 

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

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

 exceeding in size those of the young Wombat above compared. 



