As already stated, the _Tetraonidæ_ are pre-eminently characterized
among gallinaceous birds by their densely feathered tarsi, and by the
feathers of the nasal fossa or groove, which fill it completely, and
conceal the nostrils. The toes are usually naked (feathered to the claws
in the Ptarmigans), and with pectinations of scales along the edges. The
tail-feathers vary from sixteen to eighteen and even twenty in number;
the tail is rounded, acute, or forked. The orbital region is generally
somewhat bare, with a naked stripe above the upper eyelid, beset by
short fringe-like processes, while many genera have an inflatable
air-sac on the side of the neck.
The following synoptical table will give a general view of the North
American _Tetraonidæ_, although the arrangement is more artificial than
natural. The species of _Tetrao_ and _Bonasa_ inhabit wooded regions;
_Lagopus_ belongs to the more arctic portions of the continent and the
snowy ridges of the Rocky Mountains; the others are found in the great
prairies of the West, _Centrocercus_ being confined to the sterile
plains covered with sage or wormwood.
The following synopsis is intended to aid in defining the genera, but
does not profess to constitute a natural arrangement.
Genera.
=A.= Legs feathered to and on the basal membrane of the toes, which
are bare. No ruff on the side of the neck, which, however, has an
extensible bare space.
=Canace.= Tail broad, nearly even, or truncate, and rounded
laterally, two thirds the wing. Nasal fossæ scarcely half the
culmen.
=Centrocercus.= Tail excessively lengthened and cuneate; longer than
the wings. Nasal fossæ two thirds the culmen. Shafts of feathers on
the lower throat very spinous.
=Pediœcetes.= Tail very short, but graduated, and with the two
middle feathers (perhaps tail-coverts) lengthened beyond the rest,
and two thirds as long as the wing; the next longest half the wing.
Nasal fossæ not half the length of culmen. Shafts of throat-feathers
normal.
=B.= Legs feathered to the lower end of tarsus.
=Cupidonia.= Tail very short, truncate, but laterally graduated;
half the wings. Sides of neck with long, pointed, or lanceolate,
stiff feathers. Nasal fossæ scarcely one third the culmen.
=C.= Legs feathered to the claws.
=Lagopus.= Tail about two thirds the wing, truncate; of sixteen to
eighteen feathers. Most species becoming white in winter; none of
the other genera exhibiting this peculiarity.
=D.= Lower half of tarsi bare, with two rows of scutellæ anteriorly.
=Bonasa.= Sides of neck with a ruff of broad, truncate, soft
feathers. Tail very broad, square, as long as the wings.