24 ON THE CliASSIFICATION OP BIRDS. 
fact, appears to be, that the aberrant genera of the two 
groups approximate so closely that we might almost 
suspect Icteria formed part of the Crateropodmte, did 
we not believe that there is still another form to be dis- 
covered, which would unite the two subfamilies even more 
closely. The genus Ixos, after all, may be continued 
in artificial systems, but cannot be adopted in natural 
classification ; since it includes genera long before de- 
fined ; and unites, under one name, birds which actually 
belong to different families. 
(23.) Quitting the aberrant circle, we enter among the 
true thrushes(il/erM/!Ji«,Sw.),exhibitingthetypical per- 
fection of the whole family. Our preceding remarks will 
tender it unnecessary to repeat the leading distinctions of 
these birds ; and they are fully illustrated by our blackbird, 
throstle, and fieldfare : these, by their pointed wings and 
even tail, constitute one of theprincipal divisions {Merula 
11.); another includes the mocking-birds (^Orpheus); a 
third, the rock-thrushes {Petrocincla') ; and a fourth is 
probably represented by the African genus Cheetops. If 
the perfection of the thrushes depended on the powers of 
their voice, the American mocking-bird would stand 
unrivalled : it is, indeed, the Orpheus of the feathered 
tribes ; and has found an historian in Wilson, at once 
faithful and poetic. The true thrushes {Merida), like 
all other groups pre-eminently typical, are dispersed over 
all parts of the world ; but the mocking-birds {Orpheus) 
are found only in America. Some of the species so 
nearly approach the long-legged thrushes {Crateropo- 
dina) that the junction of the two groups becomes un- 
questionable. 
(24.) The rock-thrushes open a passage to the next 
division {Myotherinm Sw.), comprehendingalarge assem- 
blage of birds found only in the tropics, where they live 
chiefly upon ants. As these are to be searched for upon 
the ground, we accordingly find the legs very much de- 
veloped, and much more adapted, in their general struc- 
ture, for walking than for perching ; the wings, as being 
little used, are feeble ; and the tail sometimes so short 
