Systematic Position of the Sheath-bills. 153 



la its osteological features the Sheath-bill presents certain 

 resemblances to the Oyster- catcher. Nevertheless, the 

 Oyster-catchers are not so fundamentally specialised away 

 from the Limicolse^ and the two groups are separated 

 by enough deep-seated and important characters as to 

 appear to forbid their being closely associated together, the 

 likenesses between them being presumably the result of 

 environmental or functional stresses. Garrod, for instance 

 (P. Z. S. 1877, p. 417), comparing Chionis and Hamatopus, 

 says : " Nevertheless, although these birds are both schizo- 

 rhinal, their skulls give indications of a very different affinity. 

 Hcematopus possesses supra-occipital foramina, basipterygoid 

 articulations, and a bifid vomer." Again, he goes on to 

 add : " My dissections of both C. alba and C. minor are 

 quite in favour of a larine affinity .'' 



It would be idle to deny that the skulls of the Sheath-bill 

 and the Skua do not present very striking and remarkable 

 resemblances. Moreover, it is in just those characters in 

 which the skull of a Skua difters from the skull of a Gull 

 that it resembles those of a Sheath-bill. But to declare 

 that these characters are of such importance that they point 

 to a close affinity between the Sheath-bills and Skuas, 

 other than that they are members of the same order 

 (Charadriiformes) or even of the same suborder (Laro- 

 Limicoke), would be another matter ; for there is the 

 question of parallelism and plasticity due to similar super- 

 ficial stresses to be eliminated. My observations seem to 

 warrant the opinion that the Skuas are more generalised, 

 and stand closer to the true Limicolse (Charadriidse + 

 Scolopacidse) than do the Gulls (Laridse) or the Auks ; but 

 the more attentively one examines the osteological features 

 proper to and peculiar to a large series of difl'ering 

 charadriiforin groups, the more impressed one becomes 

 with the idea that each one of such groups represents a 

 distinct evolutionary entity, which stands by itself and 

 which had its origin in an independent process of discon- 

 tinuous variation from a common stock. It is easy to say 

 that such a series of groups merely represent the present-day 



