110 TEETIAET VERTEBEATA OF THE FAYtTM. 



the middle into a longitudinal ridge, such that when the tooth is worn the resulting 

 wear-surface of the main cusp is continued back on this median elevation of the talon. 



The next tooth [pm. 3) is larger and especially wider ; it also consists of a high 

 anterior portion and a posterior talon. The anterior part is composed of three cusps, 

 one of which forms the antero -internal angle of the tooth, Avhile behind this the 

 other two imperfectly separated cusps form a transverse ridge. In wear, the abraded 

 surface of the antero-internal cusp is continuous with that of the outer one of the 

 transverse pair, and this again unites with the surface of the talon, which has a ridge 

 towards its outer side, rising into a tubercle posteriorly. 



The last premolar {pm. 4) is wider, and its anterior cusp is less distinctly developed 

 than in pm. 3. On the other hand, the inner cusp of the transverse pair is much 

 larger and more prominent. The talon also bears a more distinct postero-external 

 cusp. In the third and fourth premolars the cingulum is slightly developed on the 

 outer and posterior sides ; on the latter it forms the raised edge of the talon. 



The first molar (PI. IX. fig. 2, m. 1) consists essentially of a pair of transverse ridges, 

 each composed of a pair of tubercles and a small talon. The inner tubercles are 

 somewhat higher and sharper than the outer, which are the most worn. There 

 is a tendency to form small tubercles in the valley between the two main ridges, 

 connecting the inner ends of the outer tubercles. The talon consists of a blunt 

 tubercle nearly in the middle line, and a smaller, often obscure, cusp on the inner 

 side. In the third molar (m. 3) the talon is much larger, the main cusp being larger 

 and tending to become subdivided into two, while the inner cusp also is prominent, 

 so that in this tooth the talon forms a third transverse ridge. This third molar 

 is extremely similar to the corresponding tooth in some mandibles of PalcBomastodon, 

 while m. 1 and m. 2 difi"er considerably, owing to the small development of the third 

 lobe ; but at the same time the differences are merely of degree and not of structure. 

 The cingulum is well developed on the outer side of the lower molars. 



Of the milk-dentition only the last lower milk-molar is known. This is well shown 

 in a portion of the right ramus of a young mandible (text-fig. 43), in which 

 mm. 4 and m. 1 are well preserved, and beneath the former the crown of pm. 4 is 

 present. Mm. 4 is much like the permanent molars ; it is bilophodont with a small 

 talon forming the rudiment of a third ridge. 



Vertebral Column. — The vertebral column of Moeritherium is fairly completely 

 known. In several cases vertebrae have been discovered associated with portions of 

 skulls and teeth that can be definitely determined as belonging to M. lyonsi; and in 

 addition to these an almost complete vertebral column has been found associated with 

 a very imperfect skull which is undoubtedly that of a species of Moeritherium, though 

 whether of M. lyonsi or not is uncertain. The vertebrse known to belong to M. lyonsi 

 will be described, first. 



In the atlas (PL XI. fig. 1) the deep cups for the occipital condyles (cond.) in correlation 



