SCOTT : LITOPTERNA OF THE SANTA CRUZ BEDS. 89 



and bear low, spine-like, incipient metapophyses : on the other hand, the 

 postzygapophyses are of the normal thoracic type, placed on the under 

 surface of the neural arch and very large. 



In the middle portion of the thorax (PI. XII, fig. 7) the vertebras have 

 larger and more depressed centra, with kidney-shaped faces ; the trans- 

 verse processes are prominent, but short and rod-like, and the metapophyses 

 are prominent ; the neural canal is small and the spines have a remarkably 

 strong backward inclination ; the zygapophyses are long, extremely narrow 

 and widely separated. In the posterior thoracic region (PL XII, fig. 8) 

 the centra become longer, broader and more depressed, while the trans- 

 verse processes are greatly reduced, becoming vestigial on the last two or 

 three vertebrae. Curiously enough, on the last four or five vertebras the 

 transverse processes have no articulation with the ribs, which is not true 

 of Diadiaphoriis or Theosodoji, but does occur in the Santa Cruz Typo- 

 theria. Probably the final thoracic is the anticlinal vertebra, as in the 

 two genera last named, and on what is presumably the antepenultimate 

 vertebra the postzygapophyses assume the lumbar pattern. 



It is exceedingly likely that there were six lumbar vertebrae, and the four 

 preserved are the last and probably the first, third and fourth. Assuming 

 the formula of six, the length of the loins is to that of the skull as 86 : 100, 

 and the entire length of the trunk, measured around the curve of the spinal 

 column, is 251, when the basal length of the skull is taken as 100. The 

 anterior and median lumbars have long, rather slender and depressed 

 centra, with distinct ventral keels, broad, plate-like and antroverted trans- 

 verse processes, and broad spines with moderate forward inclination ; the 

 zygapophyses are cylindrical and interlocking, the metapophyses are greatly 

 reduced and the neural canal is large. Compared with those of Protero- 

 thermm, these vertebrae are distinguished by their more slender transverse 

 processes, the smaller metapophyses and the less inclined spines. The 

 last lumbar (PI. XII, fig. 9) is quite different from those described ; it has 

 a wide, very much depressed centrum, with broad anterior and extremely 

 small posterior face ; the transverse processes are very broad and each has 

 on its anterior border near the centrum a small, slightly convex facet for 

 the fifth vertebra, and on the posterior border a much larger, deeply 

 concave surface for the prominent convexity on the pleurapophysis of the 

 first sacral : each of these posterior facets is actually larger than the hinder 

 face of the centrum. The neural canal is broad and the somewhat narrow 



