248 Transactioiu. — Zoology. 



Defining, as usual, the first thoracic vertebra as the first in which the 

 ribs articulate with the sternum, there are seen to be seven presacral 

 thoracic vertebrae, free save for a union of their spines by ossified liga- 

 ments. The last, or eighth, thoracic vertebra is ankylosed with the com- 

 pound sacrum. The same number is found in Ocydronms and Porphyrio, in 

 Tribomjx there are nine thoracic vertebrae. These vertebrae do not differ in 

 any important respect from those of the allied genera ; and even if it were 

 necessary I could not describe them in detail, as it was not possible for 

 me to have the skeleton disarticulated. 



It is to be noted, however, that the entire thoracic region is propor- 

 tionally shorter in Notornis than in either of its three allies. This is shown 

 in fig. 3, in which the line xy corresponds pretty nearly with the anterior 

 boundary of the thorax in all four figures, while the line x"y", which is 

 taken through the anterior end of the pelvis in Notornis, and consequently a 

 little in front of the hinder extremity of the thoracic region, passes in the 

 other three figures well in front of the pelvis. 



The eight thoracic ribs of each side are flattened bones, divided, as usual, 

 into sternal and vertebral portions ; five of the sternal ribs articulate with the 

 sternum, their ventral ends being less crowded together — owing to the 

 greater length of the costal edge of the sternum — than in Ocydronms, but 

 more so than in Forj^liyrio. Four of the vertebral ribs, the second to the 

 fifth inclusive, have uncinate processes, as in Trihomjoc and Forphyrio ; in 

 Ocydromiis there is an uncinate process also on the first thoracic rib. The 

 position of the uncinate processes in Notornis is similar to that in Ocydromiis ; 

 they are situated nearer the sternal ends of the ribs than in Porplujrio; in 

 Trihonyx their position is about intermediate. 



The compound " sacrum " contains one thoracic, five lumbar, apparently 

 four true sacral, and six caudal vertebra. As far as I can make out these 

 numbers hold good for the other three genera, but in adult specimens it 

 is not easy to decide the exact number of true sacrals. Behind the last 

 ankylosed caudal vertebra come four free caudals ; from the analogy of the 

 allied genera these were probably followed by two or three ordinary vertebrae 

 and a pygostyle. 



Sternum and Shoulder -girdle. 



The sternum of Notornis, as shown by the above table of comparative 

 measurements, and by pi. XX., is as nearly as possible of the same propor- 

 tional length as that of Trihonyx, while it is considerably longer than that of 

 Ocydronms, and shorter than that of Porphyrio. Its breadth, proportionally 

 to length of trunk, is considerably greater than in either of the three allied 

 genera. The proportions of the sternum are, however, best seen by reducing 

 it in all four genera to the same absolute length ; this is done in figs. 4 



