Systematic Position of the Sheath-bills. 141 



In any case, however, we must be cautious in drawing 

 deductions as to affinity from the resemblances noted in the 

 parietal region in the Sheath-bills and the Skuas, for this 

 might indicate that it was rather that tlie Skuas were more 

 Plover-like than the Gulls than that the Sheath-bills were 

 more Skua-like than the Plovers. 



A word may be added in connection with the general 

 shape and configuration of the frotito-parietal region in the 

 Sheath-bills. Shufeldt (Journ. Anat. & Phys. Lond. vol. xxv. 

 1891, p. 509) has thus expressed himself upon it : "As for 

 the vault of the skull and the greater portion of its posterior 

 aspect, particularly the supraoccipital region, it is all 

 strongly gallinaceous in the Sheath-bill, and strikes us at 

 once upon the most superficial examination." Such a simi- 

 laritv, whether it exists or not, \\ould lu^t appear to have 

 much importance one way or the other, but I am obliged to 

 confess that personally I have failed to see the resemblance. 

 As an indication of any gallinaceous affinity in the Sheath- 

 bills, the statement seems to call for criticism, and to be 

 misleading. 



Frontal Region. — The morphological details of this region 

 will be more obvious from an inspection of the accom|)anying 

 text-figures than from any amount of written description. 

 These text-figures depict the skulls of various numbers of 

 the Sheath- bill family as seen from above. Three of them 

 represent skulls of Chionis alba, in which we observe variation 

 due apparently to age and ossification, or very possibly to the 

 influences of isolation ; another represents the skull of 

 Chionarc/ms minor, and another the skull of CJdonarchus 

 crozettensis. 



As is obvious from the figures, the main features of this 

 aspect of the skulls of the Sheath-bills are the strongly 

 marked and deep supraorbital depressions, Avhich are merely 

 separated in the middle line by a thin sagittal ridge, and 

 the very peculiar and distinctive shield-like lacrymals. As 

 regards the supraorbital depressions, these, in form and 

 structure, are obviously modifications of what is seen in the 



