272 
Professor Owen on the 
continental species, which I propose to call PhascoUmys latifrons, 
the upper incisors present a transverse setni-oval or rather renifornt 
section, the convex enamelled surface being directed forwards and 
outwards: this surface is feebly striated longitudinally : the op¬ 
posite or concave surface is impressed by a shallow longitudinal 
groove. The entire incisor is more curved than that of the Phas- 
colomys Vomhatus; i. e. it describes the larger segment (nearly 
one half) of a smaller circle. In Phase. Vomhatus the outer or 
enamelled surface of the upper incisor is indented by a shallow 
longitudinal groove, as well as the opposite side, which is the most 
convex transversely. The entire incisor describes about one- 
fourth of a larger circle. The lower incisors are narrower in 
Phase, latifrons, and trihedral; the enamelled anterior or under 
surface is flat; the outer surface longitudinally impressed, and 
almost devoid of enamel. In Phase. Vomhatus the lower incisors 
are also trihedral, but the outer surface is convex and enamelled • 
the entire teeth, and the symphysis of the jaw supporting them 
are relatively larger. The first lower molar (premolar) is relatively 
larger, the last relatively smaller in Phase, latifrons. 
In this species the intermaxillary part of the skull is higher in 
proportion to its width, less convex externally. The nasal bones 
are relatively broader, forming the whole upper surface of the 
anterior third of the skull in Phase, latifrons. The inter-orbital 
part of the skull is relatively much broader in Phase, latifrons 
and is produced on each side into a well-marked supra-orbital 
ridge and post-orbital process, both of which are almost obsolete 
in Phase. Vomhatus. The temporal fossae are not bounded, as in 
Phase. Vomhatus, by two nearly parallel and remote longitudinal 
ridges, but are continued by a convex, rather irregular tract 
to near the middle of the upper region of the cranium. 
A very remarkable feature in the skull of the Phase, latifrons 
is the supra-tympanic cell excavated beneath the base of the 
zygoma: this cell in Phase. Vomhatus is transversely oblong 
simple, one inch by half an inch in size; in Phase, latifrons it 
extends inwards one inch and a quarter, and expands to an 
antero-posterior diameler of one inch and a half, and a vertical 
diameter of one inch, having an oblong outlet nearly one inch in 
length and half an inch in depth, slightly contracted in the middle. 
