22 EINAR LONNBERG 
and I am thus able to confirm MATHEws' interpretation. The shafts of the 
remiges of the type specimen are entirely white, and those of the rectrices 
only partly on the concealed parts pale brownish. I have also the opportunity 
of stating that the feathering of the forehead of this type specimen extends 
well forward on the bill approaching the nostril within less distance than the 
length of the latter. As this feature also is characteristic for the Gygzs of the 
Atlantic, it is evident that SPARRMAN’s name a/éa must be used for the same. 
For the Gygzs of the Pacific several different names have been used, and 
it is not easy to decide which of them ought to be applied to the birds from 
Easter Island. G. mzcrorhyncha Saunders is, of course, excluded on account of 
its white shafts, different tail &ca. GMELIN’s name cazdzda belongs typically 
to the White Tern of the Hawaiian group, while the bird from the Kermadec 
Islands, which is said to be considerably larger than the former, has been named 
royana by MATHEWS. As the dimensions recorded by MATHEWS for the latter 
come rather near to those of the present specimens from Easter Island it does 
not appear impossible that they belong to the same race, although MATHEWS 
says that he believes the Easter Island birds to »represent another race». 
Not long ago E. W. GIFFORD has publisked a paper (Birds of the Gala- 
pagos Islands &ca. Exp. of the Calif. Acad. of Sc. to the Galap. Isl. 1905 
—06. Proc. Calif. Acad. of Sc. 4th Ser. Vol. II. Aug. 1913) which throws 
some light on the variation of the Pacific Gygzs, which, evidently, is rather 
considerable. It will thus appear that it is difficult to attach so great im- 
portance to the difference of a few millimetres with regard to the length of the 
wing of these birds as some authors have done. GIFFORD has examined and 
measured 20 specimens of Gygzs from Clipperton and Cocos Islands and found 
that the length of the wing of the males varies from 223 to 260 mm. and that 
of the females from 231 to 254 mm. (average in the former case 244, in the 
latter 241). MATHEWS’s G. a. voyana as well as the Easter Island birds fall 
_thus within the limits of the variation of the Cocos Island birds in this respect. 
The culmen of GIFFORD’s birds varied between 36,; and 43 mm. with an 
average for males of 40,2, for females of 39,2 mm. 
I have not had any opportunity of examining specimens from Hawaii, 
but professor REICHENOW has kindly provided me with measurements of 10 
specimens of Gygzs from the Palau Islands, and from this communication it is 
seen that four males have the length of wing from 245 to 250 mm., two fe- 
males have the same measurement 248 and the remaining four unsexed ones 
from 233 (22) to 250 (f2), while the length of the culmen in the whole lot 
varies between 38 and 43 mm. 
The difference between these dimensions and those recorded by MATHEWS 
for G. a. royana are not very great. It is thus rather doubtful if not most of 
the White Terns of the Pacific simply should be termed Gygzs alba candida 
Gmelin, and it is only with hesitation that I have used the name voyana above. 
Mr. BACKSTROM found White Terns on Motu Nui as well as on Rano 
Raraku of the main island. The nesting places were similar to those of Pro- 
celsterna. 
