THE VOYAGE OF THE ' CHALLENGER.' 



399 



united in front, where they are produced triangularly downwards ; behind, 

 their inturned ends do not unite either with each other or with the 

 pessulus, or with the second semi-rings. These last, as well as the 



Fig. 5. 



Syrinx of Garrodia nereis, from before. 

 a. The last tracheal ring, from below, to show the pessular bar. 



Fig. 6. 



The same, from behind. 



third, fourth, and fifth, on which is inserted the muscle, are all similar 

 in shape, and separate from each other ; they are closely approximated 

 in front, gradually getting shorter posteriorly. 



Garrodia, which may be considered typical of the Oceanitidae, is ante- 

 riorly (fig. 5) almost the same as Pelecanoules, but the first, second, and 

 third bronchial rings are complete (fig. 6). The last tracheal ring bears 

 a complete pessulus (5, a). 



A very similar type of syrinx prevails in the other Oceanitidae, and is Zool. Chall. 

 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 



