104 R. S. Lull — Cretaceous Armored Dinosaur, 



behind the rib, so that the section of the bone at this point 

 is roughly L-shaped. Further out, the rib becomes T- 

 shaped in section, as its upper surface extends in front 

 as well as behind. In the last pair of these ribs the 

 vertical portion becomes practically obsolete at mid- 

 length, and the bone becomes a thin blade-like expansion 

 which merges into the thin inner margin of the ilium just 

 in front of the acetabulum. This rib is clearly visible 

 in plate II, and resembles the diapophyses of the three 

 following sacral vertebrae very closely when viewed from 

 above. The three anterior pairs of ribs were not visible 

 from above, except for a fragmentary impression of one 

 (pi. II), as they had been broken away beyond the 



Fig. 3. — Caudal vertebrae of Nodosaurus textilis. Bight lateral aspect. 

 One-fifth natural size. Nos. 9 and 10, 16 and 17, 23 and 24, in contact in 

 matrix. 



preserved limitations of the sacral armor. It was only 

 upon preparing the ventral side that they became evident 

 (pi. III). The spinous processes of the entire syn- 

 sacrum are coalesced into a continuous vertical plate 

 of bone, the summit of which is visible at intervals in 

 plate II, s, where the armor is lacking. 



In the sacro-caudals, the first pair of ribs are typically 

 T-shaped in section and extend, as do the second pair, 

 outward and somewhat backward. The first pair evidently 

 abutted against the posterior portion of the ilium, as a 

 slight depression exists in about the right place. The 

 restoration of the rib has been made accordingly. The 

 presacral ribs probably extended to the ilium, as in 

 Polacanthus and in the pelvis of Ankylosaurus on exhibi- 

 tion in the American Museum of Natural History, and 



