212 TBETIAEY VEETEBEATA OF THE FATtTM. 



postero-exteinal main cusp. The inner side of these comparatively small molars is 

 considerably higher than the outer. 



The dimensions (in centimetres) of the mandible and teeth just described are: — 



Length from anterior end of symphysis to end of molar series . 15"5 



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 : — 



Length. Width. 



m.l 1-6 1-3 



m.2 1-9 1-5 



m.3 2-2 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 inno^ninatum. 



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 Halithermm. In the third (1) 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 vertebrae are like those of Halitherium, but the haemal 

 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 the other 

 vertebrae, and the anterior zygapophyses are also considerably elevated. The transverse 

 processes rise from the ventro-lateral borders of the centrum and curve backwards 

 and downwards. The whole vertebra diff'ers 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 (PL XX. fig. 6) is preserved in which the arch is comparatively 

 low with a short neural spine ; the centrum is transversely oval, with a slight median 



