This important and well-known group, embracing as it does by far the greater number of valuable non-aquatic game birds, merits a very full and careful presentation. Although perhaps most abundantly represented in the Northern Hemisphere, they are nearly world-wide in distribution, and are especially well represented in North America. The group comprises about one hundred and twenty-five species, disposed in some twenty-three genera, which are distinguished from the Pheasants, among other characters, by the absence of spurs on the tarsi, and by having the head entirely feathered except sometimes over the eyes. Although as thus circumscribed they form a relatively compact group, there are considerable differences, not only in size, but in certain minor characters, which serve as a basis for separating them into several small well-marked groups that have at times been regarded as of subfamily or even higher rank. In the first of these that we shall consider, embracing the Grouse, Partridges, etc., the nostrils are wholly feathered and the tarsus is half or usually entirely hidden by feathers, while in some the feathering extends quite to the tip of the toes.