248 Transactions.—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 vertebre, 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 Ocydromus and Porphyrio, in 
Tribonyx there are nine thoracic vertebre. These vertebre 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. 8, in which the line zy corresponds pretty nearly with the anterior 
boundary of the thorax in all four figures, while the line 2'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 10 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 Ocydromus, but 
more so than in Porphyrio. Four of the vertebral ribs, the second to the 
fifth inclusive, have uncinate processes, as in Tribonye and Porphyrio; 
Ocydromus there is an uncinate process also on the first thoracic rib. ee 
position of the uncinate processes in Notornis is similar to that in Ocydromus s 
they are situated nearer the sternal ends of the ribs than in Porphyrio; ® 
_ Tribonyx their position is about intermediate. 
The compound “ sacrum ”’ contains one thoracic, five lumbar, apparently 
four true sacral, and six caudal vertebre. As far as I can make out si 
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 yertebre 
and a pygostyle. 
Sternum and Shoulder-girdle. i 
The sternum of Notornis, as shown by the above table of comparative 
measurements, and by pl. XX., is as nearly as possible of the same propor 
tional length as that of Tribonyx, while it is considerably longer than 
Ocydromus, and shorter than that of Porphyrio. Its breadth, proportionally 
to length of trunk, is considerably greater than in either of the three #"™ 
genera. The proportions of the sternum are, however, best seen by rede 
it in all four genera to the same absolute length; this is done 12 figs- 
