of the Genus Stenomylus. 307 



scarcely larger than a pin hole, from which I judge that the 

 tooth was vestigial. The second premolar stands isolated with 

 a considerable diastema on either side of it, and like the third 

 premolar is still a single-cusped tooth. The grinding tooth of 

 the lower jaw is the fourth premolar, and this is developed as 

 a large three-lobed, molariform tooth, with high crescentic 

 cusps, and deep pits in each lobe. In all the specimens this 

 tooth is Avell worn as though it had been used for grinding 

 grass some time, which is the reason that I have assigned the 

 age of one year to the individuals with this and the first molar 

 just showing, as is uniformly the case. 



Cervical vertebrce. — The neck as a whole is long and slen- 

 der, each constituent vertebra being markedly elongated, as is 

 usual among Tylopoda. The atlas is relatively long and nar- 

 row, the anterior cotyli being deeply excavated to make the 

 articulation for the occipital condyles. In the lower side the 

 two .articular facets are separated by a groove in S. hitchcocki 

 (confluent in S. crassipes), while on the upper side the two 

 cotyli are separated by a wide notch. The posterior ends of 

 the transverse processes are prolonged backward to make short 

 horn-like projections, which extend behind the facets for the 

 axis much as in Poebrotherium. The posterior facet for the 

 axis is high and inflexed along the upper border, for the under 

 side of the odontoid process. The edges of the transverse pro- 

 cesses makea nearly straight line, in contrast to the sinuous 

 one commonly found. The vertebrarterial canal enters the 



Fig. 10. Fig. 11. 



Fig. 10. Stenomylus hitchcocki, atlas seen from the dorsal side, x 1/2. 

 Fig. 11. Axis seen from the side, x 1/2. 



neural pedicle just to one side of the axial facet and passing 

 through the arch comes out again about the middle of the 

 centrum. The first spinal nerve had its exit adjacent to the 

 anterior opening of the vertebrarterial canal. 



The axis is also a long and slender bone, with a long, low 

 spinous process ending to the rear in two small tubercles, a 

 feature very characteristic of the camels. The transverse 

 processes begin just in front of the middle of the centrum and 

 make moderately expanded wings to either side, their outer 



