404 



ON THE PETRELS COLLECTED DURING 



Zool. Chall. Aeipetes antarcticus (figs. 20, 21, p. 407), commonly placed in the genus 

 Exp. vol. iv. Thalassceca with Thalassceca glacialoides, completely differs in the struc- 

 ture of its syrinx from the last three species described, and is more like 

 Prion. The two first pairs of bronchial rings are complete anteriorly, 

 Ibid p 38. the second being ossified, for a small extent only, in the middle line. 

 The lowest tracheal ring is quite simple anteriorly, and posteriorly it 

 sends forwards a pessuliform process, anchylosed in front with the second 



Ibid. p. 36. 



Fig. 15. 



Syrinx of Thalassceca glxcialoides, from before. 

 Fig. 16. 



Ibid. p. 38. 



The same, from behind. 



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 &c., ossified posteriorly 

 in their median (narrowest) portion only to bear the tnicheal septum. 



