280 



CAPT. D. M. S. WATSON ON SEYMOURIA, 



small and hourglass-shaped and separated from one another by 

 an interval of more than their own length. The neural arch 

 rests on the anterior part of the centrum and presents a large 

 articular face to the space between the centra ; the lower part of 

 this space is in part filled up by the top of the chevron, but there 

 can be no doubt that the condition in life was essentially embolo- 

 merous, the cartilaginous intercentrum not having ossified. 



Text-figure 9. 



Seymouria bayloriensis Broili. Ribs, X 1. 



The numbers are tbose which the bones drawn occupy in the series. 

 Cau. IV. &, V. are caudal ribs. 



Bibs. — The general distribution and structure of the ribs have 

 been well described by Williston, to whose account, however, I 

 am able to add some details of interest. 



The long slender atlantal rib is double-headed, the capitulum 

 and tuberculum being carried at the ends of two widely separated 

 branches. 



The upper part of the 5th r,ib, which has a very expanded 

 distal end, is extraordinarily deep and massive. The two heads 

 are widely separated, the capitulum articulating with a special 

 process on the intercentrum. 



From here backwards the ribs are more slender, and in the 

 middle of the back the tuberculum is merely a facet on the upper 

 edge of the rib, and not carried out as a special process. 



The sacral ribs cannot be described in detail. The caudal ribs 

 are remarkably long and massive, they are well curved, and if 

 found separately would have been regarded as dorsals, 



