SCOTT : LITOPTERNA OF THE SANTA CRUZ BEDS. 21 



of these vertebras have been found in association with any one individual. 

 The lumbars (PI. IV, figs. 4-5) have elongate and rather narrow centra, 

 which are but moderately depressed ; they are quite sharply constricted in 

 the middle and have low, sharp ventral keels ; only in the last vertebra 

 does the centrum become notably broad and low. The neural canal is 

 quite small and the neural spines are relatively short, with a strong for- 

 ward inclination ; transversely these spines are much compressed and thin, 

 antero-posteriorly they are broad at the base, narrowing to the tip ; the 

 zygapophyses are cylindrical and interlocking, as in the posterior tho- 

 racic region, and the metapophyses are very prominent. On most of the 

 lumbars the transverse processes are long, depressed, tapering and antro- 

 verted, but on the last two they are short and very broad, becoming on 

 the last one broader than the antero-posterior diameter of the centrum 

 and forming a pair of exceedingly large plates ; on the anterior border of 

 each process is a well-defined articular facet for a corresponding surface on 

 the transverse process of the penultimate lumbar, and on the hinder bor- 

 der a still larger one for the first sacral. 



The sacrum consists of six vertebrae, of which only the first two sup- 

 port the ilium ; the centra diminish in size posteriorly, becoming very 

 small in the last three vertebrae, as does also the neural canal. None of 

 the sacral vertebras has a neural spine, but the metapophyses of the last 

 four are connected by high, continuous ridges, making this region trans- 

 versely concave : the neural arches are not everywhere continuous, but 

 leave a median vacuity between each successive pair of vertebrae. On 

 each transverse process of the first sacral is a large convexity, which articu- 

 lates with the concave facet on the transverse process of the last lumbar, 

 as already described. 



No caudal vertebrae of this genus have yet been identified, but, from 

 the small size of the last sacral and the great reduction in the diameter of 

 its neural canal, it is evident that the tail must have been short. 



A few fragments show that the ribs are laterally compressed and plate- 

 like and, though not very broad, they are of the usual ungulate character. 



Nothing is yet known of the sternum. 



Appendicular Skeleton. — The skeleton of the limbs and feet is very 

 fully known. The scapula (PL I) is known, as yet, in only two genera 

 of this family, Diadiaphorns and Proterotherium, and, though the bone is 

 quite different in shape in these two genera, there are no structural differ- 



