18S9.] ^"^ ^ (C<»pc. 



Measurements of Cranium. 



Length of true molar series 0">G5 



' . „ J, 1 f anteroposterior 020 



Diameter of second true molar J ' 



( transverse 0^0 



Diameters second premolar ] 



anteroposterior 022 



transverse 022 



Vertebra. — The axis is preserved except the anterior part of the centrum, 

 •which is wanting. The posterior cup is deep and oblique, and the hypapo- 

 physial keel is strong, acute and well produced posteriorly. The neural 

 spine is, as usual, a keel which is well produced forwards. Its superior 

 border is thin and is arched, the greatest elevation being a little anterior 

 to the middle. A. tuberous ridge descends on each side to the base of the 

 postzygapophysis. The latter are large, and with articular surfaces a 

 little oblique. The parapophyses originate at the middle of the centrum, 

 and are quite narrow and acuminate in form, their apices reaching be- 

 yond the line of the superior border of the cup of the centrum. The ver- 

 tebrarterial canal is not enclosed ; it is represented by a groove with a 

 narrow angular edge below. Its anterior marginal perforation is enclosed 

 b}'^ a narrow bridge. This vertebra differs from that of Equus caballus in 

 the greater anterior extension and greater acuteness and form of border of 

 the neural canal ; in the narrowness and deep separation of the parapo- 

 physis, and non enclosure of the vertebrarterial canal. 



The seventh cervical is not perforate for the vertebral canal. The ex- 

 tremities of the rather depressed diapophyses are thickened and a little 

 recurved, and their bases send a thin keel posteriorly along the side to the 

 costal articulation. While the cup is subround, the ball is compressed, 

 and its surface extends over the anterior two fifths of the base of the cen- 

 trum. The hypapophysial keel is marked and acute, and rises to a tuber- 

 cle at the middle of its length. The zygapophyses are large, the posterior 

 plane and a little oblique ; the anterior more oblique, and a little concave. 

 Neural spine compressed and very short. 



The dorsal vertebrae are distinctly opisthocoelous, and their sides and 

 inferior edge are gently concave. The hypapophysial keel appears on 

 the posterior centra. The diapophyses have the usual form, are on the 

 superior part of the neural arch, are directed upwards, and support an 

 obtuse metapophysis. Just posterior to their base is situated the double 

 spinous foramen. On posterior dorsals this foramen becomes single and 

 is situated above the line of the base of the diupophysis. In one of the 

 latter vertebra; there is a fossa in the anterior costal fossa. The neural 

 spines become very elevated posteriorly, are narrow in front and shallowly 

 grooved behind. The anterior ones are slightly concave in anterior out- 

 line. The postzygapophyses are merely oval facets at the base of the 

 spine ; the prezygapopliyses are not well defined. 



The last lumbar is opisthocoelous and has a much depressed centrum. 

 Its diapophyses are very wide in both directions, and bear articular faces 



PROC. AMER. PHILOS. SOC. XXVI. 130. 3d. PRINTED JUNE 5, 1889. 



