345 



less open angle than in Phascolomys medius, in which, as in the recent species, it 

 extends forward nearly on the same parallel with the line of the alveolar outlets. 



A shallow channel marks the inner surface of the commencement of the diastemal 

 border (ib. fig. 1, 21'), its course being from above obliquely forward; there is a feeble 

 rising of the surface anterior thereto. The palate between the ridges is regularly arched, 

 the span being 1 inch 6 lines, the depth or height of the arch 1 inch. The extent 

 preserved just reaches the place of entry of the prepalatal or " incisive" foramina, showing 

 from the nasal cavity the hind wall of those canals and the increased vertical extent of 

 the free inner surface of the premaxillary, making the sudden deepening of this part of 

 the palate when viewed from below in such specimens as have that part entire, such as 

 the subjects of fig. 2, Plate LVIL, & fig. 2, Plate LVIII. a, from the smaller extinct 

 species, Phascolomys medius. 



The fractured surface of the premaxillaries (Plate LX. fig. 5) exposes the incisors 

 near the apical end of the long pulp-cavity, about 1 inch 3 lines above the diastemal 

 ridge : the premaxillary increases in thickness as it rises to form the alveolus. The upper 

 fractured surface of the present fossil (Plate LX. fig. 4) exposes part of the floor of the 

 nasal passages, gradually descending as they retrograde toward the place of the post- 

 palatine apertures. Most of the intermolar floor of these passages and roof of the mouth 

 has been broken away. 



On each side of the nasal passages appear the hollow implanted ends of the molar 

 teeth. That of d 3 (fig. 4) projects above the prezygomatic ridge, that of d 4 between 

 this and the front pier of the zygoma (21*); and the relative position of the rest 

 conforms with the generic type of these singular elongate, outwardly curved, ever- 

 growing teeth. 



The total length of the first and smallest, following the curve, is 2 inches 9 lines. 

 The long diameter of the oval or subtriangular grinding-surface is 6 lines ; the breadth 

 near the base, which is backward, is 5 lines. The inner enamelled side extends forward, 

 with a very slight outward bend, from the axial line of the skull to the apex, which is 

 narrow and obtuse, and round this the enamel bends for a short way along the outer 

 side of the tooth ; this is the longest side, and curves from behind forward and inward 

 to the apex more strongly than does the inner side. The enamel can be traced from the 

 inner side over the greater part of the hind surface of the tooth. The coat of cement 

 covering the outer side of the tooth can be traced over parts of the enamel, the whole 

 of which it seems originally to have covered. 



The grinding-surface of the second molar (d 4) gives 9 lines in fore-and-aft diameter, 

 6 lines across the hinder lobe ; that of the third molar (m 1) has the same longitudinal 

 with rather less transverse extent ; and the two succeeding teeth diminish, chiefly in 

 transverse thickness. The grinding-surface of the last molar (m 3) has a fore-and-aft 

 extent of 6^ lines, Avith a transverse diameter at the hind lobe of but 3 lines. In shape, 

 implantation, and structure, showing interruption of the enamel coating at the outer side, 

 these upper molars closely adhere to the generic character of Pliascolomys. The exposed 



