OSTEOLOGY OF THE ARMORED DINOSAURIA. 



93 



The oval plates are succeeded by two or more of a subrectangular outline with 

 rugose bases having but little transverse thickening, but not cleft longitudinally 

 except in young individuals. Their approximate shape is shown well in plate 14, 

 although some of the upper portion is missing from plates 10 and 11 (pi. 14); these 

 are in turn followed by the thin subtriangular plates of the sacral and anterior 

 caudal region. Good examples of this latter style are shown in plate 24, figures 3 

 and 4. In these plates I am unable to find differences that would enable one to 

 determine the exterior from the interior surfaces. The bases are symmetrical, both 

 surfaces equally rugose, and evenly covered with vascular grooves. 



Caudal plates. — In the consideration of the remaining dermal structures of the 

 tail a second specimen, No. 4714, in the National Museum supplements the one 

 just described to such an extent that it is possible to give an accurate account of 

 the entire dermal series. 



This specimen consists of an articulated series of 44 caudal vertebrae with the 

 plates of one row and the 

 dermal spines in sequential 

 position (fig. 58). The rela- 

 tive positions of these ele- 

 ments as found was deter- 

 mined from an accurately 

 drawn map (fig. 5S, also Dia- 

 gram 5, map of quarry 13, 

 pi. 37) made at the time the 

 fossil was collected. 



A comparison of these 

 vertebrae with those of the 

 articulated skeleton (No. 

 4934) indicates that between 

 5 and 7 vertebrae are lacking 

 from the proximal end to 

 complete the caudal series. 

 It was also observed that the 

 largest plate occupied the same relation to the tail as the corresponding plate in 

 the Stegosaurus stenops skeleton. (Compare p u , pi. 3, with pi. 13.) This appar- 

 ently •■establishes the position of the largest plate to be above the base of the tail, 

 as correctly placed by Marsh in his first restoration (pi. 32, upper figure), and not, 

 as in later conceptions, above the sacral region. 



Posterior to this plate and in regular order are three other plates of diminishing 

 dimensions, as in No. 4934. (PI. 24, figs. 4, 3, 2, and 1; compare with caudal 

 plates No. 4934, pi. 2.) 



Measurements demonstrated the fact that the length of the remaining articu- 

 lated caudals, i. e., to a point where the dermal spines attach, exceeded by S inches 

 (206 mm.) only, the total longitudinal diameter of the three plates, barely enough 

 to account for the interspaces between the plates. This would appear to show 

 that there were only three plates posterior to the largest of the series, or six for the 

 two rows. Adding this number to the 14 actually shown in position more anterior 



Fig. 58.— Sketch from diagrams 5 and 7 of map of quarry 13 showing 

 relative positions of dermal plates and caudal vertebrae in tail 

 of stegosaurus stenops. cat. no. 4714, u.s.n.m. <z, anterior caudal 

 vertebrae; 6, dermal spines with tip of tail (see plate 14). 10, 75, 

 76, and 177 original quarry numbers of dermal plates. 



