138 Mr. P. R. Lowe on the 



V. The Comparative Osteology of the Chionidida. 



In the many papers which have been written on the subject 

 of the anatomy and affinities of the Sheath-bills, so much 

 stress has been laid on tlie affinities of these birds with the 

 Oyster-catchers (Ha^matopodidse) that attention has been 

 apparently distracted from certain Skua-like features in the 

 skulls of this group. In the following notes (of a somewhat 

 general character) I shall endeavour to demonstrate these 

 Skua-like features ; but just as I believe that such Oyster- 

 catcher-like characters as are presented in the skeletal 

 features of the Sheath-bills are not necessarily evidence of 

 close affinity, but may have been impressed on them through 

 functional or environmental stresses or through mere 

 parallelism, so I would not be taken as implying that because 

 in the skull of the Sheath-bill there are certain features 

 which bear a strong resemblance to similar features in the 

 skull of a Skua, that this necessarily implies that the Sheath- 

 bills are more closely related to the Skuas than to any other 

 Charadriiform group (see also Summary). Incidentally I 

 shall hope to demonstrate that the gap which separates 

 the Skuas (Stercorariidae) from the Gulls (Laridae) is much 

 greater than has apparently been hitherto suspected. 



Finally, there is another point to which I think attention 

 should be drawn. There is a somewhat time-honoured 

 belief that gallinaceous and. columbiform characters are 

 reflected in the osteological peculiarities of the Sheath-bills. 

 For this belief and for the statements which have been made 

 in this connection, there appears to be no real evidence at 

 all. If the Sheath-bills possess any gallinaceous or colum- 

 biform features at all, they are concerned with the most 

 superficial characters. 



The Skull. 



Occipital Region. — The occipital condyle is circular (not 

 bi-lobed as in (Tallinse), and a distinctly constricted neck is 

 to be observed. The occipital foramen (foramen magnum) 



