The general characters of this family have already been given on p. 2,
as distinguished from the _Turdidæ_. The relationships are very close,
however, and but little violence would be done by making it a
subfamily of _Turdidæ_ or even a group of _Turdinæ_, as was done in
the “Birds of North America.”
While the group is very well represented in the Old World, America has
but one peculiar genus _Sialia_, and another _Saxicola_, represented
by a single species, a straggler, perhaps, from Greenland on the one
side and Siberia on the other. The diagnostic characters of these are
as follows, including _Turdus_ to show the relationships of the three
genera:—
Turdus. Tarsi long, exceeding the middle toe; wings reaching to
the middle of the tail, which is about four fifths the length of
the wings. Bill stout; its upper outline convex toward the base.
Second quill shorter than fifth.
Saxicola. Tarsi considerably longer than the middle toe, which
reaches nearly to the tip of the tail. Tail short, even; two
thirds as long as the lengthened wings, which reach beyond the
middle of the tail. Second quill longer than fifth. Bill
attenuated; its upper outline concave towards the base.
Sialia. Tarsi short; about equal to the middle toe. Wings
reaching beyond the middle of the tail. Bill thickened.