REPTILIA: SEYMOURIA 55 



that the head of the rib articulated with them on the sides. The 

 sutures separating the arch from the centrum are not visible in the 

 adult specimens. 



The single sacral vertebra resembles that immediately pre- 

 ceding, except that it is larger and stouter, but no wider, and its 

 diapophyses are very heavy and stout, though not extending farther 

 outward. The arch was somewhat injured in preparation, and I 

 can say Uttle regarding its spine, though enough is left to indicate 

 that it was longer than on the vertebrae immediately in front. It 

 probably was nearly as long as the spine of the first caudal vertebra. 

 Five caudal vertebrae are preserved in position, together with a 

 part of the sixth. Their arches, it is seen, are very much narrower 

 than those of the presacrals, but their centra, at least in front, 

 are not much smaller. The spines are elongate, rather slender, 

 and pointed, and are directed obliquely backward. The dia- 

 pophyses do not extend outward as widely as those of the sacrum. 

 The chevrons, preserved on the fourth and fifth vertebrae, are 

 unusually stout. 



Many of the ribs cannot be exposed in their entirety. The 

 transverse processes of the atlas and axis do not bear ribs, but, 

 lying below them and above the clavicle on the left side are two 

 slender ribs, partly exposed, that evidently belong here. From the 

 third vertebra to the ninth the articulated ribs are expanded dis- 

 tally and quite surely overlap each other at their ends, since the 

 antero-posterior extent of the middle ones is greater than the length 

 of the centra bearing them. The terminal expansion is greatest 

 on the sixth, where the width is twenty millimeters. The expan- 

 sion of the seventh is materially less than that of the sixth, 

 and that of the ninth is not more than two or three times greater 

 than the width of its shaft. As far as the eighteenth or nineteenth 

 at least — as far as I am able to follow them — the distal end is sKghtly 

 greater in breadth than the width of its shaft. In length the ribs 

 do not vary much, at least the first eighteen or twenty pairs do 

 not. Posteriorly the ribs are clearly double-headed, and I believe 

 that they are so throughout, though I cannot be quite sure of the 

 first three or four pairs. 



The single sacral rib on each side has a heavy tubercle for union 



