472 THE WASATCH FAUNA. 



diameter of that of the last lumbar, and is subround, and somewhat oblique, 

 the inferior border being the more prominent. 



Of the eleven caudal vertebrge preserved, five, and perhaps six, are con- 

 tinuous from the sacrum. These diminish rapidly in bulk, retaining uniform 

 length. The articular faces are subround; the anterior have them rather 

 oblique, appropriately to the descending direction of the tail at the base. 

 The diapophyses are present on the six, but very small on the sixth. They 

 are depressed, acuminate, and turned backwards. The neural spines of the 

 first and second are elongate but not elevated They are squarely truncate. 

 The inferior face of the centrum of the first caudal is round transversely, 

 and concave anteroposteriorly. On the second the middle line below is 

 narrowed medially and expanded posteriorly. In the third this feature is 

 more marked, the posterior expansion being concave medially. On the 

 fourth and fifth there is a strong median rib, which divides into two poste- 

 rior ribs, giving small surfaces for chevron bones. On the sixth the me- 

 dian inferior rib is gone. Distal to this point the centra increase in length. 

 The neural canal is reduced to a groove between two widely spreading 

 tuberosities in front, and two closely approximated ones at the posterior ex- 

 tremity. The diapophyses are represented by a small process at each ex- 

 tremity of the centrum, of which the posterior disappears first. On the 

 inferior face, the anterior extremity is more protuberant downwards than 

 the posterior, and the median and chevron ridges are gradually effaced. 



In comparing this column with that of the P. primcevus, the principal 

 differences are seen in the numbers of some of the series. In that animal 

 the dorsals are probably fifteen, the lumbars are six, and the sacrals four. 

 In the present species they are, dorsals fourteen; lumbars seven; sacrals 

 three. The diff'erence in the number of the sacrals is more important than 

 that of the lumbars and dorsals It is only necessary to shift one from the 

 lumbar to the dorsal series in the P. primcevus, to have an agreement with 

 the P. vortmani. The centra of the cervical vertebrae are a little shorter in 

 the P. vortmani than in the P. primcevus, and the caudal diapophyses are 

 more depressed and not so robust. The metapophyses are already distinct 

 on the ninth dorsal vertebra in the P. primcevus, while they first appear on 

 the twelfth in the P. vortmani. 



