134 TlMEHRI. 
Catalogue, are : — length of body 13^ inches ; colour 
bluish slate, inclining to leaden grey ; upper and under 
tail coverts grey : while in the other, R. leucopygus, the 
characters are :— -total length 18 inches; colour slaty 
black, with a brownish shade ; upper and under tail 
coverts white. Now it must be mentioned that these 
measurements are based on specimens, the sex of which 
is not stated in the catalogue ; while the difference in the 
size of the male and female specimens in this genus is 
often quite as wide apart as the measurements given 
above for the two apparent species ; and at the same 
time, the shades of colour, bluish slate, and slaty -black, 
are but terms applicable at different states to the same 
bird in its passage from the yellowish-brown plumage of 
the young to the black of the adult. The character of 
the grey or white tail coverts is also one of doubtful 
value, since these parts vary as much as from white to 
grey, and from these to creamy white, in birds of the same 
size, though of different ages and of different colours 
over the other parts of the body. In both species, 
the tail is grey or greyish black, with a white or creamy- 
white base, and a white tip, succeeded by a broad sub- 
terminal bar of 4 black. There are specimens in our 
Museum collection, identified at the Zoological Society 
as R. sociabilisy in which the length of the bird exceeds 
16 inches; and while in a large set of forms there are to 
be found smaller specimens that seem to fit in with the 
description of R. sociabilis, and larger that seem 
referable to /t\ leucopygus % yet there are considerable 
differences in the shades of their plumage, and of the 
special character of the tail coverts, and the size of bird, 
that make one suspe6l that the two species, generally 
