40 THE VOYAGE OF H.M.S. CHALLENGER. 
Gstrelata mollis is quite similar, except that the box is composed of one ring less.! 
In Diomedea brachyura and exulans the calibre of the trachea diminishes very 
considerably below the place of insertion of the sterno-tracheales. The syrinx (figs. 
29, 30) is strong and well ossified. The fifth bronchial semi-rings on which end the 
fanned-out tendinous insertions of the intrinsic muscles are strong and much arched. 
The four preceding bronchial rings, as well as the last tracheal, are ossified anteriorly 
and posteriorly, and (with the exception in Diomedea exulans of the fourth bronchial) 
co-ossified anteriorly into a strong box, with which the penultimate tracheal ring is 
also connected in the middle line. Behind, the last two tracheal and first bronchial 
rings are co-ossified forming a broadly triangular pessular bar or box, whilst one 
or more (5) of the preceding tracheal rings have patches of ossification mesially. 
Fig. 29.—Syrinx of Diomedea exulans, from before. Fic. 30.—The same, from behind, 
About natural size. About natural size. 
In Thalassiarche culminata (of which I have only examined one) all the five bronchial 
rings, including the muscular one, are firmly co-ossified together, and free from the 
rest. There is no complete pessulus, the bony box formed by tae rings terminating 
posteriorly in a straight and free margin, which a cuneate bar, formed by the inturned 
anterior ends of the fourth bronchial rings, does not reach. The syrinx of Phabetria 
as yet I only know from a young specimen, in which the bronchial rings below the 
first are incomplete anteriorly, whilst behind there is a box formed by the last two 
tracheal and first four bronchial rings. 
Majaqueus is very like Diomedea in its syrinx, the penultimate tracheal ring, 
however, being ossified anteriorly, as well as its five successors, which remain free in 
1 T regret not having as yet been able to examine any adult bird of Wstrelata brevirostris, all my specimens being 
young and consequently with the tracheal rings unossified and generally distinct. There is a box formed by the 
fusion behind of at least three of the bronchial rings with the last, or two last tracheal ones, The second, third, and 
fourth bronchial rings are united together anteriorly, the third rings joining the pessular bar. 
