Nodosaurus textilis Marsh. 



107 



sacral 5 corresponds to my first sacro-caudal and shows 

 a rib which is nearly as robust as that of sacral 4 and 

 which runs nearly parallel with it and is coalesced with 

 the posterior portion of the ilium. Another vertebral 

 centrum which is partially detached Hulke calls a caudal ; 

 in Nodosaurus the equivalent of this is coossified with the 

 rest and forms the second sacro-caudal. In front of 

 sacral 1 of Hulke there are ^ve pairs of slender, rather 

 irregular ribs apparently partially attached to the over- 

 lying armor. In a later figure by Seeley (1892, fig. 1) these 

 are shown as lying above the ilia but beneath the armor. 

 There is no evidence that this is true in Nodosaurus, for, 



Fig. 4. — Eight radius and ulna of Nodosaurus textilis. Inner oblique as- 

 pect, r, radius; u, ulna. One-eighth natural size. 



as Lydekker (1892, p. 85) remarked, the position of the 

 ilium of Polacanthus internal to the ribs is a character 

 found elsewhere only in adult tortoises, in which it is 

 probably due to the impact of the shield on the ribs, 

 thus rendering it impossible for another bone to grow 

 between them, a condition which would not occur in 

 Nodosaurus because of the lateral limitations of the 

 sacral shield. 



The pelvis of Nodosaurus differs from those of both 

 Polacanthus and Stegopelta in the absence of dermal 

 armor from above the ilia. In both genera mentioned, 

 the armor is firmly coalesced with the ilia, although in 

 the character of the sacral armor Stegopelta is nearer 

 its contemporary Nodosaurus than is Polacanthus. 



