252 Transactions. — Zoology. 



Porphyria. In the general form of the ilium and in the relative proportion 

 of prae- 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 (pi. 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 ]Dubes 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 

 under consideration no longer fall into the same order as when arranged by 

 the shoulder-girdle and sternum. As before, Tribonyx is intermediate 

 between Porphyria and Notornis, but Ocydromus can no longer be placed in 

 a du-ect series with the others, since, by the size of its pelvis, it comes 

 between Porphyria 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 Eails under consideration 

 shows that Sightlessness is accompanied by the following structm-al 

 peculiarities: — 



a. The carina sterni is diminished. 



b. The sternum is widened, and the transverse sternal angle is 



increased. 



c. The manubrium, or rostrum sterni, disappears. 



d. The coracoid grooves recede from the middle line. 



e. 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- 

 ria 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 examination of the skeletons shows that Mr. Gould's sagacity was not 

 at fault. In nearly every respect, Tribonyx is intermediate between Porphy- 

 ria and Notornis, approaching more nearly to the latter ; the only exceptions 



