2 Q4 



S. W. WILLISTON 



Fig. 2. — Trimerorhachis. Skeleton, from above, 

 as restored from specimen shown in Fig. i. One- 

 fourth natural size. 



Thirty-one precaudal 

 vertebrae are visible, all 

 in close articulation, the 

 first one apparently with 

 the condyle. That the 

 vertebral column was 

 very flexible is evident 

 from its sinuosity as it 

 lies in the matrix, with- 

 out break. The general 

 structure of the verte- 

 brae is well known from 

 isolated specimens. 

 The pleurocentra are 

 very small, and the 

 intercentra are more or 

 less U-shaped, indicating 

 a large amount of carti- 

 lage. The spines are of 

 nearly uniform height 

 throughout the column, 

 curving backward and 

 upward, and slightly 

 dilated at their extrem- 

 ities. Their height 

 above the plane of the 

 zygapophyses is nowhere 

 more than 14 mm.; their 

 width at the ends from 

 8 to 10 mm. 



The ribs are preserved 

 very completely in posi- 

 tion; all have been ex- 

 posed on one side or 

 the other except two, 

 near the middle. The 

 first eight are the 



