PEOrESSOE OWEN ON THE SPECIES OP PHASCOLOIITS. 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 (PI. LVI. fig. 3)'. 



The subsymphysial foramina (PL LVI., r, r) 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 cuxle, 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 (PI. LII. fig. 3, e, PI. LIII. fig 3, e) 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 (P\. LII. fig. 1, ?, figs. 2, 2') are sub- 

 compressed, with a narrow subelliptic transverse section (fig. 2'), of which the long axis 

 is dkected from before rather outward and backward. Those of Phascolomys lati- 

 frons (PL LIII. fig. 1, i, 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 iilatyrhinus 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 (PL 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', c), is greater 

 in Phascolomys latifrons than the unenamelled tract in Phascolomys platyrhinus. 



The first upper molar in Phascolomys platyrhinus (PL LII. fig. 1, & fig. 3, d s) 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, e), 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. c). 



' In the type specimen {torn. cit. pi. Ixxi. fig. 6, d) it is 4 inches 8 lines. 



3e2 



