38 THE VOYAGE OF H.M.S. CHALLENGER. 
line. The lowest tracheal ring is quite simple anteriorly, and posteriorly it sends forwards 
a pessuliform process, anchylosed in front with the second bronchial rings. Two pairs 
of the bronchial semi-rings (3, 4) are ossified at their posterior extremities, but not fused 
in any way. The penultimate tracheal and preceding rings are, as in Fulmarus, &e., 
ossified posteriorly in their median (narrowest) portion only to bear the tracheal septum. 
This, however, is not (vide fig. 18, a) a complete septum, but is incomplete, the incurved 
posterior ends of the rings not reaching the anterior wall of the trachea by some little 
way. Its vertical extent is small, ceasing about ‘85 inch above the bronchi. 
The peculiar genus Bulweria is, perhaps, as far as regards tracheal structure, nearer 
the small Storm-Petrels (Procellaria and Cymochorea) than any other group, judging at 
least from my examination of the syrinx of Bulweria macgillivrayt. In this specimen * 
the rings are asymmetrical,—there being only three, instead of four, bronchial rings 
between the pessular ring and that which bears the muscle on the left side, apparently 
owing to the suppression of the second bronchial ring, as may be seen in the figures (figs. 
22, 23),—and irregularly developed, tending thus to hide the typical form. The last 
Fre. 22.—Syrinx of Bulweria macgillivrayi, from before. Fia. 23.—The same, from behind. 
three tracheal rings are, anteriorly, more or less united, there being a pessular bar 
developed on the inferior margin of the last ring. Posteriorly, the ante-penultimate 
of these is quite free and complete ; the next is incomplete posteriorly, whilst the last is 
complete on the right side, but anchyloses on the left with the first bronchial laterally. 
The third bronchial rings on each side are complete, thus encircling the bronchi. The 
fourth is free and incomplete. 
Puffinus (as represented by Puffinus brevicauda) presents a simple form of syrinx 
(figs. 24, 25), the two first bronchial rings being complete anteriorly, the succeeding 
two being only semi-rings. The two last tracheal are united with the two first 
bronchial behind, sending off a pessular process, which anteriorly, as usual, is continuous 
with the third semi-rings. In younger birds (fig. 26) the various rings concerned 
remain more distinct, the pessular bar, it is pretty clear, being largely formed by the third 
* Some of the peculiarities here described may be due to its being a youngish bird. I haye, unfortunately, as yet 
sn mable to examine the syrinx of Bulweria columbina, which might throw some additional light on the subject of 
the affinities of this genus. 
