252 Transactions.—Zoology. 
Porphyrio. In the general form of the ilium and in the relative proportion 
of pre- and post-acetabular regions, Notornis approaches most nearly to 
Tribonyx, while it deviates, on the whole, in the greatest degree, from Ocy- 
dromus. ‘The excess in size of the pelvis is most marked in its transverse 
dimensions. This is well shown in figs. 8 and 8a (pl. XXI.), in which the 
four pelves are drawn of the same absolute length. 
The ischia and pubes of Notornis are widely divergent ; so much so that 
the pubes can be seen throughout nearly their whole length in a dorsal 
view. In the other three genera they fall well within the outer boundary 
of the ilia. This is most pronounced in Ocydromus, in which the obturator 
notch (ob.) is not seen in a ventral view, being completely hidden by the 
pubis. In the other three genera, it is well seen internal to the pubis. 
Thus, arranged according to the characters of the pelvis, the four genera 4 
under consideration no longer fall into the same order as when arranged by : 
the shoulder-girdle and sternum. As before, Tribonyx is intermediate 
between Porphyrio and Notornis, but Ocydromus can no longer be placed in 
a direct series with the others, since, by the size of its pelvis, it comes 
between Porphyrio and Tribonyx, while in many of its pelvic characters it 
goes off on a special line of its own. 
Summary and Conclusions. 
To sum up: an examination of the four Rails under consideration 
shows that flightlessness is accompanied by the following structural 
peculiarities :— 
a. The carina sterni is diminished. : 
6. The sternum is widened, and the transverse sternal angle is 
increased. 
The manubrium, or rostrum sterni, disappears. 
The coracoid grooves recede from the middle line. 
The coracoid becomes more nearly vertical in position. 
The coraco-scapular angle is increased. 
g- The coracoid and scapula decrease in all dimensions, and the 
furcula decreases in thickness. 
h. The pelvis increases in size, and the acetabulum is relatively 
thrown forward. 
Professor Owen, from the examination of the fossil bones referred to 
above, considered Notornis to be intermediate in characters between Porphy 
rio and Ocydromus. Nothing could have been nearer the truth than this, if 
we were unacquainted with Tribonyx, to which bird Mr. Gould, from a con- 
sideration of external characters, considered Notornis to be most nearly allied. 
An 
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