PROFESSOR OWEN ON THE SPECIES OF PHASCOLOMYS. 355 
9 lines. In a second specimen, with a length of 5 inches 9 lines the breadth is 5 inches 
3 lines. In a Ph. latifrons with a mandible 4 inches 10 lines in length, the extreme 
breadth is 4 inches 4 lines. In a second specimen the mandible, with a length of 
5 inches, has a breadth of 4 inches 7 lines (Pl. LVI. fig. 3)*. 
The subsymphysial foramina (Pl. LVI., 7, 7) are usually closer together in Phascolomys 
platyrhinus (fig. 1) than in Phascolomys latifrons (fig. 3). 
§ 4. Dental Characters of Phascolomys. 
The dentition of Phascolomys is unique in the mammalian class; its formula is well 
known ; every tooth enjoys unceasing growth, is consequently rootless, and is curved in 
the segment of a circle, it has also a partial investment of enamel. This is not the case 
with the molars of any rodent, nor of any other marsupial save the Wombats. In the 
upper molars (Pl. LII. fig. 5, e, Pl. LIII. fig 3, ¢) the enamel is laid upon the inner, in 
the lower molars (Pl. LVII. figs. 6 & 7) on the outer side. It is coated, with the rest 
of the tooth’s surface, by cement. 
The upper incisors in Phascolomys platyrhinus (Pl. LII. fig. 1, 7, figs. 2, 2') are sub- 
compressed, with a narrow subelliptic transverse section (fig. 2'), of which the long axis 
is directed from before rather outward and backward. Those of Phascolomys lati- 
Frons (Pl. LITT. fig. 1, 7, figs. 2, 2'), with a fuller subelliptic section, have the long axis 
directed from before more outwardly as it extends backwards. The pair of teeth present 
a broader surface forward; in Phascolomys platyrhinus they present a broader surface 
outward,—the surface in both species being the convex enamelled one; the enamel in 
both, also, is longitudinally striate. A larger proportion of the upper incisor is coated 
with enamel in Phascolomys platyrhinus (P\. LII. fig. 2') than in Phascolomys latifrons 
(Pl. LIII. fig. 2’). Commencing in the former near the hind border, it extends along 
the outside, over the front border, and along the inner side to a longitudinal indent, 
three fourths of the way toward the hind border. The enamel in Phascolomys latifrons, 
commencing at the hind border, which is, rather, the outer one, extends over the fore 
part and upon the inner surface to where it bends to form the hind surface. The extent 
of this hind part of the tooth, coated only with cement (Pl. LIII. fig. 2', ¢), is greater 
in Phascolomys latifrons than the unenamelled tract in Phascolomys platyrhinus. 
The first upper molar in Phascolomys platyrhinus (P1. LIL. fig. 1, & fig. 8, d 3) presents 
a subtriangular transverse section or working-surface, the base being backward, the apex 
forward ; the inner side is shorter than the outer side, and is indented near the apex by a 
groove traversing the tooth lengthwise; the outer angle of the base is sometimes, by 
oblique attrition, produced. The enamel begins anteriorly at the outer part of the apex 
(fig. 3, ¢), opposite the groove, is continued inward and backward, and upon the base 
two thirds of the way toward the outer angle, which, with the outer side of the tooth 
to near the anterior angle or apex, is coated only by cement (ib. ¢). 
1 In the type specimen (tom. cit. pl. Ixxi. fig. 6, d) it is 4 inches 8 lines. 
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