212 
TERTIAEY VERTEBRATA OF THE FAYtTM. 
postoro-external main cusp. The inner side of these comparatively small molars is 
considerably higher than the outer. 
'Die dimensions (in centimetres) of the mandible and teeth just described are; — 
Leiigtii from anterior end of symphysis to end of molar series . 15’o 
Greatest width of symphysis 5-5 
Length of symphysis 6’5 
Depth of mandibular ramus beneath m. 3 4-7 
The dimensions of the teeth are : — 
w. 1 
m.2 
. 3 
Length. 
1-6 
]-n 
Width, 
1-3 
1-5 
1'4 
Vertebral Column. — On account of their massive character the ribs and vertebrae of 
Eosiren are among the commonest fossils in the Qasr-el-Sagha beds. For the most 
part, they only occur scattered in small groups or as single specimens, but occasionally 
a considerable number are found in association. The best of these sets is here noticed ; 
it includes fifteen more or less nearly perfect vertebrae associated with part of a 
skull and an os innominatum. 
The atlas is wanting. The axis is greatly abraded and broken, but in the form of 
its odontoid process and articular surfaces for the atlas it was evidently closely 
similar to that of Ilalitberium. In the third [X) cervical vertebra the centrum is 
rectangular in outline and much wider than high ; it is much less shortened antero- 
posteriorly than in later forms ; its ends are smooth and flat. The transverse 
processes are broad and long, and are perforated at their base by the vertebrarterial 
canal. Another cervical vertebra of the same series is very similar. The number of 
the cervicals is unknown. 
The thoracic and lumbar vertebrfe are like those of IlaUtherium, but the hoemal 
ridge is very slightly developed, and in the thoracic region the zygapophyses are better 
developed and the interlocking of the vertebrae is closer. 
One of the vertebrae (PI. XX. fig. 4) in the series referred to presents some peculiar 
characters. It appears to be a first lumbar ; the anterior face of the centrum narrows 
somewhat towards its neural border, the neural arch is much higher than in tlie other 
vertebrae, and the anterior zygapoj)hyses are also considerably elevated. The transverse 
processes rise from the ventro-lateral borders of the centrum and cur\'e backwards 
and downwards. 'I’he whole vertebra differs so far from the others that perhaps 
its association with them may be a matter of accident, and it may actually belong to 
some other animal. 
A sacral vertebra (PI. XX. fig. C) is preserved in which the arch is comparatively 
low with a short neural spine ; the centrum is transversely oval, with a slight median 
