180 
TEETIAET VEETEBRATA OF THE EATtlVI. 
M. 8881. 
only by ;i singlo-rooted stump, and between it and pn. 2 is a space of 2'5 cm. Pm. 2 
is a two-rooted tooth with a compressed conical crown, the anterior and posterior 
borders of which form sharp edges. A ridge runs down from the summit on the 
postcro-internal surface, dividing the inner face into a larger anterior fossa and 
a smaller {)Osterior rugose fossa, which looks inwards and backwards. The cingulum is 
develo])ed on the inner side of the tooth, particularly towards the posterior end, and it 
is also present for a short distance on the postero-external side. The third ])remolar is, 
on the whole, similar to pm. 2, from which it is separated by a short interval. The 
cingulum, however, is better developed, and forms a sort of small talon posteriorly. 
The postero-internal ridge is also more strongly developed. The fourth premolar is larger 
and is much wider posteriorly, where the cingulum forms a well-marked prominence ; 
the postero-internal ridge is still more strongly developed, its lower end almost forming 
a tul)ercle, though it cannot be said that, even in this tooth, there is any distinct inner 
cusp. The molars consist of two jtairs of cusps, the outer being crescentoid, the inner 
pyramidal ; both are much lower than in the typical Oligocene species of the genus, 
and approximate closely to the type seen in Bracliyodus, so that if it were not for the 
greatly elongated symphysis this animal might perhaps have been referred to that 
genus. In wear, the anterior limb of the postero-external crescent is seen to be divided 
into two ridges, one running forwards and inwards across the main transverse valley to 
the base of the antero-internal cusp, the other running inwards and joining a ridge 
running forwards from the postero-internal cusp, thus forming the anterior boundary of 
a fossa lying between the outer and inner posterior cusps. In Bmcliyodus and the later 
forms of Ancodon the same fossa is present, but its anterior border is formed by the 
main anterior arm of the postero-external crescent. The talon of m. 3 consists of a 
large crescent forming its outer side and a prominent ridge forming its inner edge, the 
two enclosing a well-defined fossa. The talon, as a whole, is broader and more massive 
than in the later forms of Ancodon, and is much like that found in Brachyodus. 
The dimensions (in centimetres) of this, the type specimen, are: — 
Approximate length of mandible 34 
„ „ symphysis 9 
Depth of ramus behind m. 3 4‘5 
Height at coronoid 11 app. 
The dimensions (in centimetres) of the teeth are : — 
Length. Width. 
2)1)1. 2 I'o '9 
Jim. '3 1’3 1‘1 
jmi.-i 1'3 1'2 
m.l 1-7 1-2 
m. 2 2 1 •() 
m.3 3'3 1-8 
jjength of molar series 7‘2. Lengtii of premolar series (including 
Jim. 1) 8'ti. 
The diastema between the canine and j>m. 1 is 2'2, that between />»/. 1 and jnn. 2 
is 2‘.5. 
ria.ster exist of the above sjiecimen. Made in the British Museum. 
