LIMICOL^ 355 



thinness and transparency from the thick yellowish mem- 

 brane which unites the edges of the greater number of the 

 bronchial semi-rings. 



In Larus fuscus and L. glaucus the differences are but 

 slight, and chiefly concern the greater solidity of the three- 

 way piece. 



In Larus argentatus the edges of the three-way piece 

 are most solid ; but they are connected by a series of four 

 or five bars which divide up the central region of the three- 

 way piece into alternate thicker and thinner portions. This 

 is a peculiar specialisation of the three-way piece which I 

 have not observed elsewhere. There is, furthermore, a thin 

 bony curved rod, closely applied to the outside of the three- 

 way piece, which arises from, or is at least connected with, the 

 last tracheal ring. 



Lestris antarcticus has a syrinx which is rather different 

 from that of Larus, and which points in the direction of the 

 Charadriidae, owing to the fact that the intrinsic muscles do 

 not reach the bronchial semi-ring except as a fibrous band. 

 The three-way piece, which is solid, is formed by two or three 

 tracheal rings ; there is no differentiation in membrane 

 closing bronchial semi-rings. 



It is evident from the foregoing account that, while there 

 are a few differences between the various genera of Laridse, 

 Bhynchops is quite the most anomalous form in structure as 

 well as in external appearance, as seen in its remarkable bill, 

 with its scissor-like edge and projecting mandible. Still, 

 the differences are, in my opinion, not sufficient to place 

 Bhynchops in a family by itself opposite to the remaining 

 Laridae. It seems that the usually received division of the 

 family, making an additional one for Bhynchops, will serve to 

 divide naturally the Laridse ; we may term these divisions 

 subfamilies. They will be thus characterised : — 



Subfamily I. Larinae. 



Muscle formula of the leg, AXY+. Cceca rudi- 

 mentary. Biceps slips and expansdr secuu' 

 dariorum present. 



A A 2 



