THE BEOWN-HEADED, OR MASKED GULL. 337 



to that of L. ridihundm. Through a telescope, I have frequently 

 remarked some of these birds wheu feeding, at distances between 60 and 

 100 yards, to have the black disposed as in L. capistratus ; i. e., the bird 

 when looking towards me, displayed a black head ; but when walking 

 from me, its head appeared pure white. This was particularly noted on 

 the 17th of xipril, the 3rd, 18th, 37th, and 28th of May, 1832. In favour 

 of the view that the black taking a masked form is occasional or accidental, 

 rather than transitional, is the fact, that I have seen immature birds when 

 first assuming the black head, displaying black feathers, as low down on 

 the back of the head,* as L. ridibundus ever has them at any age.f 



Fourthly. — My specimens of L. ridibimdus and L. capistratus do 

 not present any marked difference in the shade of coloiu* of the under 

 surface of the wings. — See Temminck, part ii. p. 786. 



Fifthly. — This author (p. 787) states that the eggs given to him 

 as those of L. capistratus, are rather smaller than the eggs of L. ridi- 

 bundus. Smaller individuals may be expected to lay smaller eggs, and, 

 as mentioned of those at Eam's Island, no two eggs in the same nest 

 were exactly of the same size or form. If the species be different, we 

 may certainly expect to find a difference in the eggs, but it is essential 

 that a number or series of these be seen before their differential cha- 

 racters can be properly known. 



I have many more notes in addition to those already given, which show 

 that the size of bill and feet, and length of tarsus, three of the chief cha- 

 racters by which L. capistratus is distinguished from L. ridibundus, are 

 Liable to much variation. 1 shall only add a comparison of an adult with 

 a young bird of the preceding year, which were killed from a large flock 

 at the same shot near Belfast, on the 15 th of February, 1838. 





ADULT. 



YOUNG. 





in. lin. 



in. lin. 



Length (total) 



15 9 



14 3 



„ of bill above, in a straight line . 



1 2i 



1 2 



* I once remarked a young bird of the year, in the mouth of August, with browTi 

 feathers on the head forming the regular hood ; the lower part of the back of the 

 head, as well as the upper, being of this colom-. 



t This bird is believed by Temmiuek to attain full plumage within a year ; but I 

 have often had proof of individuals, at least, not doing so until the second summer 

 after birth. 



November 1850. — An adult L. ridihundus (as I consider) of the ordinary size 

 added by Dr. J. U. Marshall to his collection of living birds in October 1849, and 

 still in his possession, exhibited a mask like that of i. capi strut us, as figured by Yar- 

 rell, during the whole of last summer. It was of a pale broccoli-brown colour. 



VOL. III. Z 



