SCOTT : LITOPTERNA OF THE SANTA CRUZ BEDS. I9 



stout and, as in all this family, is in very marked contrast to that of the 

 Macrauchenidse both in length and in the form of the individual vertebrae. 



The atlas (PI. IV, figs. 2, 2a) is relatively rather long, as well as high 

 dorso-ventrally ; the anterior cotyles are large, widely separated dorsally, 

 but closely approximated at the ventral ends ; the neural canal is large 

 and subcircular, the neural arch is thick and quite broad in both directions, 

 without spine. The transverse processes are narrow, having hardly more 

 than half the fore-and-aft extension of the atlas and there is, of course, 

 no atlanteo-diapophysial foramen ; the processes have a very elevated 

 position and ventral to them there is a deep fossa on each side of the 

 vertebra. The very short vertebrarterial canal perforates the base of the 

 transverse process. 



The axis (PI. IV, fig. 3) has a moderately elongate, broad and very 

 much depressed centrum, with prominent ventral keel ; the cotyles for the 

 atlas are low and wide and have somewhat saddle-shaped faces ; the 

 odontoid process is short, blunt and massive and is separated from the 

 cotyles by a deep sulcus on each side ; the facet for the inferior arch of 

 the atlas is very strongly convex, extending more than half-way around 

 the odontoid. The neural canal is rather small and the pedicles of the 

 neural arch are quite narrow antero-posteriorly ; the neural spine is a large, 

 prominent, hatchet-shaped plate, which projects well over the third vertebra 

 and is very different from the long, low ridge seen in Theosodon. The 

 vertebrarterial canal is of large diameter, but short, and pursues an oblique 

 course, from behind, upward and forward through the base of the trans- 

 verse process. 



The third cervical has a short and somewhat opisthocoelous centrum, 

 and a low, broad neural arch, without spine, for nearly half of its antero- 

 posterior length is overhung by the spine of the axis, leaving no room for 

 one on the third vertebra. The transverse process is a large, oblique plate, 

 short transversely, but much extended antero-posteriorly, especially for- 

 ward, where it overlaps the centrum of the axis. The fourth cervical is so 

 like the third as to call for no particular description, further than to note 

 that it has a slightly smaller and more slender centrum. The three 

 remaining cervicals have centra which progressively decrease in length, 

 though only to a moderate degree, shorter neural arches, which are more 

 deeply incised between the postzygapophyses, and an increasing develop- 

 ment of the spines. On the fifth cervical the spine is still very incon- 



