400 



ON THE PETRELS COLLECTED DURING 



line. There is always a well-developed 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 



Fig. 7. 



Syrinx of Procellaria pelngica, from before. 



Fig. 8. 



Zool. 



Chall. 

 V 



The same, from behind. 



ends posteriorly, forming a broad three-way piece ; or these rings may be 

 complete rings closely apposed, though apparently notancbylosed, 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. 



In Prion vittatm (figs. 11 & 12, p. 402), the first bronchial ring is either 

 small or fused with the second, which is anteriorly entire : this is not the 

 c ase with the three succeeding ones. The last three tracheal, and first two 

 or on one side three bronchial rings form a pessular box, continuous 

 a nteriorly with the inturued anterior ends of the third semi-rings. The 

 fourth pair takes no share in the formation of the box. In Prion deso- 

 latus there is only one complete bronchial ring, which may be the first, 

 or the first and second united ; the others are incomplete, inturned ante- 

 3d riorly , and not co-ossified to form a box. There is a good pessulus 

 borne by the last tracheal. 



In Pagodroma (figs. 13& 14, p. 403) the four first bronchial semi-rings are 

 ossified and firmly united into n bony box behind ; anteriorly, however, 



