THE UPPER TRIASSIC OF WESTERN TEXAS. 45 



The fifth series is represented by two complete median plates (fig. 16 c and d), the 

 complete plate of the outer row of the left side and an incomplete spine of the right side. 

 The median plates are similar to the preceding plates. The outer plates present the most 

 remarkable feature of the armor. Each one bears an enormous spine, over 45 centimeters 

 m length; this extends almost directly outward, but a little upward, and from its middle 



Fig. 17. — Desmatosuchus spurensis. 



A. Lower (outer) view of the lateral plate of the fifth series in the dorsal armor, 



left side. X 0.3. 



B. Posterior view of A. 



point curves backward as far as the middle of the seventh series of plates (fig. 17). The 

 base of the spine is flattened on its inner and anterior side, but is rounded on the outer 

 side. The angle between the inner and anterior faces is continued to about the middle 

 of the spine and then disappears, the section then becoming circular, which continues 

 to the acute distal extremity. The base of the plate is actually larger than the preceding 

 ones, but relative to the spine much smaller; the inner edge is thickened for attachment 

 to the median plates; the outer edge is thin and the anterior and posterior edges are 

 of about equal width. 



The accurate fit of the plates of this row permits a determination of the outline 

 of the armor at this point, and this is checked by the conjoined plates of the fourth ring 

 (see plate 8 e to h). This is most fortunate, as the position and attitude of the spine 

 would hardly be credible otherwise. The position of the great spine curving outward 

 and backward could hardly have been imagined, and its meaning is still a puzzle. 



Posterior to the fifth series the armor becomes flat and broad and descends but a 

 short distance on the sides. The plates of the median row rapidly contract antero- 



