PROFESSOR OWEN ON THE SPECIES OF PHASCOLOMYS. 357 
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 (Pl. LVII. fig. 5) is the longest, not the transverse diameter 
(ib. fig. 4). The outer surface (fig. 5, a), vertical, and slightly channelled, is divided 
by a well-marked angle from the lower surface (4), 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 (at a). In Phascolomys platyrhinus (ib. fig. 4) the 
lower enamelled surface (ib. 0) bends up upon the outer (a) 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 trian- 
gular 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’. 
The first lower molar, on the other hand, is as large in Phascolomys latifrons (P\. LVII. 
fig. 7,d 3) as in Phascolomys platyrhinus (ib. fig. 6, d 3); it is consequently larger in pro- 
portion to the size of the species, and in proportion to the other molar teeth; it has also a 
different form. In Phascolomys platyrhinus the transverse section and working surface 
of d 3, (fig. 6) is usually a full ellipse, with the long axis nearly parallel with that of the 
jaw. In Phascolomys latifrons the section is subquadrate (fig. 7). The anterior surface 
(e) usually shows a feeble longitudinal groove; the outer surface is rather narrower 
than the other three. The enamel covering it extends a short way upon the front 
surface, and then, after an interruption, is resumed upon the antero-internal angle: 
the outer enamel extends uninterruptedly over two thirds of the hinder surface. The 
other bilobed or biprismatic molars show little more than the difference of size, the 
four (d 4, m 1,2,3, fig. 3) equalling in longitudinal extent three and a half of those in 
Phascolomys platyrhinus (fig. 1). In all the species the enamel is wanting on the inner 
side of the tooth, which is nearly on a level with the inner wall of the alveolus; the 
outer wall is lower and exposes more of the tooth; the curves of the positions of the 
prismatic surfaces are reversed in the upper and lower molars. 
Mr. Waterhouse, in his instructive paper on the Dentition of the Flying Opossums’, 
pointed out two subgenera as having four true molar teeth on each side of both jaws, and 
a third subgenus as having three true molars on each side of both jaws; but the obser- 
vations on marsupial modifications of dentition were not carried further in that paper. 
In January 1839 I communicated my paper on the classification of the Marsupialia’, 
1 Trans. Zool. Soe. vol. iii. (1845), p. 306. ? Proc. Zool. Soc. 1838, p. 149. 
5 Trans, Zool. Soe. vol. ii, p. 315. 
