252 G. B. Wieland — Armored Saurian from the Niobrara. 



plate. In all the foregoing except the tubercle the thickness 

 is much as seen in the transverse section No. 2Z>. The more 

 or less median ridge is sharp and runs the entire length, being 

 of much the same height throughout its course, and terminat- 

 ing as a sharp backwardly projecting slightly upturned spur. 

 The height of the ridge is from one to one and a half centi- 

 meters. Eos. 1-6 are all plate-like and of much the same 

 thickness as shown in the middle transverse section figure 2h. 



The two elements shown in figure 7, 7a are probably a 

 terminal pair that was seated on the proximal caudal or cervi- 

 cal region, as indicated by the broad flat front edge which 

 formed a contact and the free thinner posterior edge which 

 appears to end [if not begin] the series abruptly. But the ani- 

 mal to wmich these odd bones belonged may not even have 

 been of the same species as that to which the scales of figures 

 1-6 belong and form the type. 



It is pretty clear that the form before us is allied to the 

 Stegosau ridse and is possibly included in the Ankylosauridse of 

 Brown* represented by Dinosaurs with large shields and a 

 quite rigid turtle- like back from the Judith River beds near 

 Gilbert Creek, 120 miles north of Miles City, Montana. 



The closest relationship within the family Ankylosauridae so 

 far as the dermal armature affords comparison is afforded by 

 Polacanthus as restored by JNopcsa and now on exhibition in 

 the British Museum at South Kensington. As there restored 

 there are first free plates and then a more or less perfectly 

 developed carapace only extended as such over the lumbar and 

 hip region. 



From the fact that we see the large scales shown in figure 6 

 so completely fused a lumbar-hip carapace may be supposed 

 present in the Niobrara form. But in the latter there is plainly 

 indicated by heavy sulci the presence of a system of horn- 

 shields at least as large as the keeled plates. These characters 

 evidently form a sufficient generic distinction. 



It thus seems probable that the Dinosaurs actually paralleled 

 the turtles in the development of keels of dermogene bones 

 enclosed by horny shields and coming near to the formation of 

 a true carapace with a clearly aligned bone and hornshield 

 system primarily comparable to that of Dermochelys as it now 

 exists. It is not to be forgotten, however, that the unusual 

 structure of the Archelon carapace described in previous pages 

 makes it very likely that ere long a turtle may be found with 

 a neural, pleural and marginal series greatly reduced and 

 mainly replaced by rows of large shields not greatly unlike 

 those now described. 



Yale University Museum, New Haven, Conn. 



* The Ankylosauridae, a new family of Armored Dinosaurs from the Upper 

 Cretaceous ; by Barnum Brown. Bull. Amer. Mus. Nat. Hist., vol. xxiv, 

 Art. XII, pp. 187-201, New York, Feb. 13. 1908. [Though I fail to see why 

 the Nodosauridae of Marsh are ignored in this paper.] 



