SCOTT : LITOPTERNA OF THE SANTA CRUZ BEDS. 87 



uncertain. Of the present genus I have 4 cervical, 8 thoracic, 4 lumbar and 

 2 sacral vertebrae, most of them belonging to a single individual. A care- 

 ful comparison of these with the complete back-bone of Theosodon makes 

 it appear probable that the number was a little greater than in that genus ; 

 viz., C. 7, Th. 15, L. 6. All of the vertebrae preserved resemble the cor- 

 responding ones of Proieyothenum, though much smaller and lighter, and 

 there are many differences in points of minor importance. 



The atlas (PI. XII, figs. 3, 3«) is short, broad and high dorso-ventrally ; 

 the anterior cotyles are large, widely separated dorsally, but quite closely 

 approximated ventrally, and slightly emarginated in the middle of the 

 lateral border. The neural arch is thick and convex and the spine is 

 reduced to a vestige. The posterior cotyles are small and nearly plane 

 and are not connected with the fossa on the inferior arch, which is narrow 

 and deeply concave, but quite short antero-posteriorly ; the hyapophysis is 

 a spine-like tubercle on the hinder edge of the inferior arch. The verte- 

 brarterial canal is very short, opening anteriorly into a large fossa on the 

 side of the neural arch, which is deeper and better defined than in the atlas 

 of Proteyotherinm. The atlanteo-diapophysial notch shows no tendency 

 to become a foramen, as there is no process from the anterior border. 



The axis (PL XII, fig. 4) has a curiously shaped centrum; seen from 

 below, it is of subquadrate outline, the anterior width exceeding the length. 

 Anteriorly, the centrum is broad, much depressed and very thin dorso- 

 ventrally, behind the transverse processes it narrows and thickens, mak- 

 ing the posterior face trihedral ; the ventral keel is well defined, though 

 not very prominent. The anterior cotyles for the atlas are low and broad, 

 of irregularly trapezoidal outline, the outer border exceeding the inner in 

 dorso-ventral length : the articular surface is saddle-shaped, concave trans- 

 versely and convex dorso-ventrally. When the atlas and axis are placed 

 together, there appears to be a surprising lack of adjustment between the 

 respective articular surfaces, which would necessitate the presence of un- 

 usually thick cartilages to make up for this. One's first suspicion natur- 

 ally would be that the two bones belonged to different animals, but the 

 conditions under which they were found seem to exclude such a possi- 

 bility. The odontoid process is strikingly long and slender and of irregu- 

 larly cylindrical shape, which is in marked contrast to the short and heavy 

 process of Diadiaphorus. On each side of the base of the odontoid is a 

 deep and narrow sulcus, separating it from the cotyles. The transverse 



