Systematic Position of the Sheath-bills. 125 



well-known authority has found no evidence pointing to its 

 former residence there, and the same deduction applies to 

 Lord Rothschild's collections from the same locality in so 

 far as they have been worked out. Nor has the Sheath-bill 

 been recorded on any of the expeditions entering Antarctica 

 by way of Queen Victoria or Edward the Seventh Lands. 

 From what has been written of Antarctica as a connecting- 

 link between South America and Australasia, such a limited 

 distribution in Antarctic seas is interesting. 



Osteologically the two groups above mentioned are 

 characterised by perfectly obvious differences, which are, 

 however, practically confined to the skull. There are also 

 very obvious and distinct differences in more superficial 

 characters, such, for instance, as the wattling and caruncu- 

 lation of the face, the colour of the soft parts, the arrange- 

 ment of the horny sheath embracing the upper mandible, 

 and the presence or absence of bare spaces on the side of 

 the face. 



In spite of such manifest generic differences, Milne- 

 Edwards (Ann. Sc. Nat. ser. 6, xiii. 1882, art. 4, p. 24) has 

 expressed the opinion that generic differentiation between 

 these two groups is unnecessary and uncalled for. In con- 

 nection with such a question it is probably not generally 

 realized that the distance separating the nearest points of 

 the territorial limits proper to the two groups is something 

 in the neighbourhood of 4500 miles, a distance which would 

 appear to be adequate enough for the deep-seated effects of 

 isolation. Even from the Crozets to Kerguelenthe distance 

 works out at something like 1500 miles. 



As regards the southern limits to which the distribution 

 of the family extends, it would appear that these are roughly 

 represented by the Antarctic circle, beyond which it seems 

 doubtful if the birds range. In the ' Ibis ' (1895, p. 165) 

 there is a note by Tristram to the effect that a specimen of 

 *' Chionis ''' was obtained by Dr. Gunn, surgeon on the 

 ' Terror ' during the Ross Antarctic Expedition, in latitude 

 78° S. Eagle Clarke (' Ibis,' 1907, p. 349) records that it 

 has been proved that Gunn was never in such a latitude, so 



