34 THE VOYAGE OF H.M.S. CHALLENGER. 
A very similar type of syrinx prevails in the other Oceanitidee, and is also that found 
in the genera Procellaria (figs. 7, 8), Cymochorea (figs. 9, 10), and Halocyptena. In all 
these the first few bronchial rings closely resemble in character tracheal rings, being nearly 
straight, closely apposed to each other, and more or less ossified. Anteriorly they may be 
united with one or more of the preceding tracheal rings, and very frequently the first two, 
or three are quite complete here in the middle line. There is always a well-developed 
Fia. 7.—Syrinx of Procellaria pelagica, from before. Fic. 8.—The same, from behind. 
and complete pessular bar, supported behind by the last tracheal ring. With this bar 
one or more (sometimes three or four) of the bronchial rings may fuse by their coalesced 
ends posteriorly, forming a broad three-way piece ; or these rings may be complete rings 
closely apposed, though apparently not anchylosed, to each other in the pessular bar. 
Different specimens vary slightly in the exact number and disposition of these bronchial 
rings, and sometimes are not exactly similar on the two sides. 
Fic. 9.—Syrinx of Cymochorea leucorrhou, from before. Fic. 10.—The same from behind. 
In Prion vittatus (figs. 11, 12), the first bronchial ring is either small or fused with 
the second, which is anteriorly entire: this is not the case with the three succeeding 
ones. The last three tracheal, and first two—or on one side three—bronchial rings 
form a pessular box, continuous anteriorly with the inturned anterior ends of the third 
semi-rings. The fourth pair takes no share in the formation of the box. In Prion 
desolatus there is only one complete bronchial ring, which may be the first, or the first 
