SCOTT : LITOPTERNA OF THE SANTA CRUZ BEDS. I27 



the anterior border of the last, is a large oval facet, by means of which 

 the processes of the two vertebras articulate. The last lumbar is further 

 characterized by the extremely large and deeply concave oval facets, much 

 larger than the posterior face of the centrum, on the hinder border of the 

 transverse processes, for articulation with corresponding surfaces on the 

 sacrum. 



The sacrum (PI. XVIII, figs. 8, 8a) is long and narrow and may consist 

 of seven vertebree, only two of which articulate with the ilia. Even the 

 first sacral vertebra has but a small and much depressed centrum and on 

 each side of it, on the pleurapophysis, is a large, convex, oval boss, for 

 articulation with the transverse process of the last lumbar, as above 

 described. On the first sacral, the pleurapophyses are large and massive, 

 making this region of the sacrum very wide ; those of the second vertebra 

 are much smaller. Posteriorly, the coalesced centra grow smaller and 

 smaller and that of the last vertebra is very small indeed. The first two 

 pairs of ventral foramina for the nerves are very large, the third pair are 

 of moderate size and the succeeding ones are minute. Functional pre- 

 zygapophyses are present on the first sacral and very small vestigial 

 remnants on the second ; behind this, not even vestiges remain. The 

 neural canal is remarkably small, even anteriorly, diminishing in size 

 posteriorly, and the hinder aperture is a mere narrow slit. The coalesced 

 neural arches are deeply concave transversely, owing to the elevation of 

 the lateral borders into high ridges. 



No caudal vertebras have yet been found, but it is evident from the 

 character of the sacrum and the greatly reduced size of the hindermost 

 centrum, that the tail must have been very short. 



The first rib is short and nearly straight, with large head set upon a 

 prominent neck, and very conspicuous tubercle ; the shaft is slender proxi- 

 mally, broadening and flattening toward the distal end. Speaking generally, 

 it may be said that the anterior ribs have large heads and tubercles, and 

 long, broad and curved shafts-, while posteriorly they become more slender 

 and rod-like. Separate tubercles are present throughout, even on the 

 last rib. 



The sternum (PI. XVIII, fig. 9), which is not completely preserved in 

 any of the specimens, is very peculiar. The presternum is long, laterally 

 compressed, and keel-like, with broader dorsal, and very thin ventral 

 border, and increasing in dorso-ventral depth posteriorly ; near the anterior 



