489 
Letters, Announcements, ^c. 
Heligoland, August 29,1878. 
Sirs, —As perhaps it may interest some of the readers of 
^ The Ibis/ I beg leave to inform you that on the 20th inst. 
—j- Larus affinis, Eeinhardt^ = X. cachmnans, Pall., =L. borealis, 
Brandt, was shot here, being the first instance of its capture off 
this island. The coloration of the back and outer wing- 
coverts forms an exact middle shade between the slaty black 
of L.fuscus and the light grey of L. argentatus. The specimen 
being in the moult for its winter-dress, the marks on the 
feathers of the neck appear darker than those of any Gull I 
know of; in fact these arrow-shaped marks may be termed 
pure black. 
About the identity of the species no doubt whatever exists, 
as I have been able to compare the specimen with one of L. 
affinis in my possession, obtained by Dr. Otto Finsch on the 
Ob during his recent Siberian excursion. 
I am, yours &c., 
H. Gatke. 
Sirs, —Through the kindness of Dr. Gunther I have been 
entrusted with the preparation of the volume of the Cata¬ 
logue of Birds containing the Sylviidse, a group of which the 
British Museum contains an excellent series from all parts of 
the eastern hemisphere. In attempting to arrange the various 
genera belonging to this subfamily, I have been obliged to 
treat some of them in a rather summary manner; and I ven¬ 
ture to bring a few of my supposed discoveries before the 
readers of ^ The Ibis,^ in the hope that their criticisms may 
confirm or dispel my doubts. 
Whilst describing the species of the genus Acrocephalus, 
I found that A. insularis (of which I have already expressed 
my opinion that A. fasciolatus was the young) was extremely 
aberrant. Firstly, it is the only Acrocephalus in which the 
young bird is decidedly yellow on the underparts. Secondly, 
it is the only species in that genus in which the rictal bristles 
are too small to be discernible with the naked eye. Thirdly, 
its tail is much more rounded than that of any of its com¬ 
panions. And fourthly, it is aberrant in having the upper 
