126 
LEUCOCIRCA, 
from the circumstance of several of the species 
having more white about their tails than any other 
fly-catcliing birds yet discovered. It is, in truth, 
now become a matter of no small difficulty in orni- 
thology to frame generic names, — expressing a 
peculiarity of structure or of habit, — sufficiently 
different from those at present in use, to answer 
the object proposed. Names taken from the various 
constructions of the bill, wings, tail, and other 
members, are completely exhausted ; while the com- 
parative ignorance in which we remain regarding 
the habits of foreign birds, is an effectual bar to our 
compounding names founded upon such circum- 
stances. "We have hardly any other resource, there- 
fore, left to us, but to employ designations derived 
from other peculiarities ; and as we find that many 
natural groups are nearly as much distinguished by 
colour as by structure, there appears no valid objec- 
tion to deriving our names occasionally from this 
source, as well as from structure or from habits. 
But to return. The sub-genus Leucocirca, as far as 
we yet know, is restricted to the tropical latitudes 
of the Old World, but more especially to India and 
its islands, where it represents the last division. 
That it immediately follows Rhipidurd , not a doubt 
