I20 REVISION OF THE PELYCOSAURIA. 



face of the vertebra, best realized from plate 17, figs. 3 and 4. Seeley has figured the 

 same condition in Deutcrosaitnis. The middle portion of the rib is sharply contracted 

 and then widely expanded antero-posteriorly and decurved, forming a vertical face for 

 a strong attachment to the ilium. The outer surface of this part is concave and the 

 inner convex. 



Fig. 46. — Lower view of same vertebra as shown in fig. 45. 



Fig. 47. — Head of a dorsal rib from D. gigas. No. 1002 University of Chicago. X 1. 



Fig. 48. — Right tide of pelvis of D. gigas. No. 4006 Am. Mus. pti, pubis ; il, ilium ; isch, ischium. X '2. 

 The posterior end of the ilium is broken away. 



There are eighteen caudal vertebrae, but none showing the elongate cylindrical 

 form that would indicate a long tail. Their general form is shown in plate 21, figs. 

 5, 6, 7. It does not differ materially from that of the caudals of Di»ietrodon incisivus. 

 The anterior caudals are very short antero-posteriorly and have nearly circular articu- 

 lar faces. The lower portion of the reverted edge is broader than the rest to accom- 

 modate the large intercentrum. The ribs rise from very low down on the side of the 

 centrum. In the mid-caudals the bottom line becomes very short, because the lower 

 half of the anterior and posterior faces are bent sharply toward the middle line (plate 

 21, fig. 6). When two adjacent vertebrae of this region are in position the beveling of 

 the lower edges forms a deep V-shaped notch, into which fits the proximal end of the 

 chevron, which has the same form as described in Dinietrodon giganhomogejies^ No. 

 112 University of Chicago (plate 21, fig. 9). In one vertebra of the middle region, 

 which is about half the size of the most anterior, the beveled portion of the lower edge 

 is nearly as great as the rest of the anterior and posterior faces. The rib is reduced to 

 a simple process from the side of the centrum. 



In the most posterior vertebrae the centra are more elongate, all trace of rib has 

 disappeared and the chevron faces are smaller. Though the vertebras are disconnected 



