THE UPPER TRIASSIC OF WESTERN TEXAS. 



43 



The second well-preserved rib is assigned to the tenth vertebra (fig. 14 c and D). 

 It is much longer than the seventh and the tubercular process is much shorter than the 

 capitular. There is still some expansion of the upper surface, though much less than 

 in the ribs anterior to it. Traces of the supporting ridge on the lower side are still 

 present. 



The third well-preserved rib is assigned to the eleventh vertebra (fig. HE and F). 

 This closely resembles the rib assigned to the tenth, but is even longer, and the expan- 

 sion of the upper surface is more closely confined to the proximal end. The capitular 

 and tubercular faces are close together, corresponding to the approximation of the facets 

 upon the vertebrae. 



A fourth well-preserved rib is assigned to the 

 twelfth vertebra (fig. 15). This rib is much stronger 

 than the preceding ones and longer. The whole rib is 

 flat and rather thin. The capitular process and face 

 are stronger than on the anterior ribs and the tuber- 

 cular face is located as a notch on the body of the 

 rib. This is the first rib that shows any decided down- 

 ward curvature of the shaft. 



In the following ribs, which are only incompletely 

 preserved, the tubercular and capitular faces are on 

 the same plane; the ribs are relatively broad in the 

 dorsal series, with a considerable outward extent, indi- 

 cating a well-rounded barrel in the animal. In the pos- 

 terior dorsal and lumbar (?) regions the ribs become 

 shorter and more slender; the capitular and tubercular 

 faces gradually approximate until they are nearly on 

 a line. 



The dermal armor (plates 8 and 9). The back 

 of Desmatosuchus was covered by a complete armor 

 consisting of four rows of plates. The presence of any 

 lateral or abdominal armor is uncertain. Aside from the presumption that such plates 

 occurred, there is a single small, irregular plate which was found intimately associated 

 with the rest of the armor and skeleton. 



The dorsal armor consists of four rows of plates arranged symmetrically in succes- 

 sive transverse series. The two inner rows are composed of flat plates with a small 

 subcentral knob; these plates increase in breadth toward the dorsal region, at the same 

 time decreasing in their antero-posterior extent. The outer rows are composed of plates 

 which have the two sides of the bases bent almost at right angles to each other, so that 

 a portion lies over the back and a portion over the sides; they bear spines which are of 

 varying height in the different parts of the body. It is probable that the median rows 

 disappeared in the posterior-caudal region, but of this there is no direct evidence. It 

 will be best to describe the plates according to the transverse series. The general 

 arrangement is shown in the plates and figures. The transverse series of dorsal plates 

 begins immediately behind the skull, but the anterior ones are not arranged in relation 

 to the vertebrae below; the first five series of plates cover the entire cervical series of 

 vertebrae. 



The plates of the first series are represented by the lateral one from the right 

 side; it is incomplete, but shows a decided spine. 



The second scries is represented by the median plate of the left side and the two 

 lateral plates. In common with all the plates of the cervical region, the median plates 

 were quite thick on the inner and outer edges and thin on the anterior and posterior 



FIG. 15. Desmatosuchus spurensis. 



A. Lower view of the twelfth rib, left 



side. X 0.3. 



B. Upper view of A. 



