2. It is more elongate antero-posteriorly, and strikingly narrower 
and more compressed laterally. 
3. In correspondence with this difference in shape the anterior 
crest (protoloph) is shorter and much more strongly recurved, while 
the posterior crest (metaloph) is directed more backward, less inward ; 
it meets the outer wall at a very acute angle, and thus makes the 
posterior valley of a different shape from that of the recent species and 
much narrower. 
4. The outer wall of the crown projects little, if at all, behind the 
postero-internal cusp (hypocone). 
5. The crista is better develojjed and fuses with the anticrotchet, 
so as to enclose a small and apparently shallow fossette. 
6. The antero-external cusp is larger, and the rib at the junction 
with the postero-external is much more prominent, while the whole 
outer surface of the crown is made more undulating by the prominence 
of this rib and by the presence of a low, broad convexity, somewhat 
behind the middle of the outer wall. 
Measiin'Dienfs. 
Second upper molar, length '062 
,, ,, ,, approximate width '044 
The other teeth, which are provisionally referred to this species, 
are much abraded, and evidently were derived from an old individual. 
In part their different appearance is due to this abrasion, but this 
would not account for the (jreat difference in transverse width. 
Making all due allowance for the fact that the type specimen is incom- 
plete at the base, it remains true that M. 2 is very narrow and M. 1 is 
very much broader, much more so than seems likely to occur in one 
and the same species. However, it would be unwise to establish 
another species upon the basis of such worn and uncharacteristic teeth 
as those before us. 
The first upper molar has none of the lateral compression which 
distinguishes the type, but, on the contrary, is subquadrate and very 
broad, the width exceeding the antero-posterior length. The tooth- 
pattern is very simple, the only accessory structure being a low, 
rounded projection, which arises from the junction of the posterior 
crest with the outer wall, and thus has a different position from the 
anticrotchet of O. bicornis. The posterior valley has been isolated by 
wear into an enamel lake, and the cingulum is prominent on the 
anterior, posterior, and internal faces of the crown. Except for the 
position of the anticrotchet, this tooth very closely resembles M. \ of 
O. bicornis in a corresponding stage of wear. 
The fourth upper premolar is also much like that of old specimens 
of the existing species. The tooth is large and subquadrate, though 
the width decidedly exceeds the antero-posterior length. The 
external wall is simply convex, and a prominent cingulum surrounds 
the inner half of the crown ; the grinding surface is extremely simple, 
the only complication being a faintly indicated anticrotchet. In mode- 
