180 TEETIAET VEETEBEATA OF THE FAT'O'M. 



only by a single-rooted stump, and between it and pm. 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 

 postero-internal surface, dividing the inner face into a larger anterior fossa and 

 a smaller posterior rugose fossa, which looks inwards and backwards. The cingulum is 

 developed 6n 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 premolar 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 tubercle, though it cannot be said that, even in this tooth, there is any distinct inner 

 cusp. The molars consist of two pairs 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 Brachyodus, 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 o£ 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 Brachyodus 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. 



j?m.2 1-5 -9 



pm.'d 1'8 1-1 



pm.4: 1-8 1-2 



m.l 1-7 1-2 



TO. 2 2 1-6 



TO. 3 3-3 1-8 



Length of molar series 7'2. Length of premolar series (including 

 pm. 1) 8'6. 

 The diastema between the canine and pm. 1 is 2'2, that between pm.l and »;».2 

 is 2-5. 



M. 8881. Plaster cast of the above specimen. Made in the British Museum. 



