SPECIES OF BIRDS. 
311 
25 . SYLVIA ROSCOE . ROSCOE’s YELLOW-THROAT. 
AUDUBON, PLATE XXIV. 
This spocies, named in honour of the celebrated 
author of the Life of Leo the Tenth , in general appear 
ranee very much resembles the Maryland yellow-throat, 
described by Wilson, but differs from it remarkably in 
its habits. 
Audubon, we think, is in the main right in the deter- 
mination of his species, although he has not stated 
precisely the grounds on which he founds his specific 
characters. The number of tail feathers is sometimes 
a good character ; thus, the sula, from Greenland and the 
Faro Islands, has ten tail feathers ; that from Iceland, 
twelve; and that from the Cape of Good Hope, fourteen ; 
and these, if the numbers are fairly given, may be con- 
sidered as distinct species. The length of the tail, the size 
of the feet, &c. are also employed in specific distinc- 
tions ; but the chief characters are those taken from 
the cranium and bill. There is something truly 
wonderful in the circumstance that creatures, which, 
in other characters, so nearly resemble each other, 
should exhibit, in the form of their crania, evident 
and characteristic differences. Those naturalists who 
have rejected this character, have never examined it 
with care. Brehm has made numerous observations on 
the forms of the crania of different species of birds, and 
on their affinities. He says, all birds which pair toge- 
ther belong to the same species, and have the same form 
of skull ; on the contrary, those that do not pair toge- 
ther belong not to the same species, and differ in the 
form of their cranium. Thus, if we examine the 
Scolopax rusticola , (w r oodcock,) and the Corvvs corax , 
(raven,) from different countries, the differences in the 
form of the cranium will arrest our attention. It is 
true, that a certain tact is required in order readily to 
detect these differences. The following illustrations in 
