PREFACE. xill 
This subject appearing to require further investigation, 
I have not removed the Masked Gull from a place among 
its generic companions in this work. I saw two examples 
of the Masked Gull this last spring, both of them birds 
that were two years old, then about to breed for the second 
time, but measuring only twelve inches and a half in length 
from the point of the beak to the end of the tail, which 
was entirely white. Arthur Strickland, Esq., of Burling- 
ton Quay, has favoured me with the measurements of a 
Masked Gull in his collection, which are as follows :— 
From the point of the beak to the commencement of the 
feathers on the top of the beak, one inch and three-six- 
teenths ; from the point of the beak to the end of the tail, 
thirteen inches; wing, from the anterior joint to the end of 
the longest quill-feather, eleven inches and three-fourths ; 
length of tarsus one inch and a half; middle toe and nail 
one inch and a half. 
A Supplement, containing figures and descriptions of 
the species obtained since the publication of the first edi- 
tion, has been prepared. 
Ryder Street, St. James, 
Oct. 1845. 
