Nostrils tubular, disjoined and lateral, or oftenest superior and united in one double-barrelled tube. Covering of bill in several pieces; bill always hooked. Hallux minute, rudimentary, or absent … _Procellariidæ_. ANALYSIS OF FAMILIES OF PYGOPODES. Feet four-toed, palmate. Hallux lobate, connected at base with base of inner toe. Tail perfect. Head closely and completely feathered. Nostrils with a depending lobe or flap. Bill straight, compressed, acute … _Colymbidæ_. Feet four-toed, lobate. Hallux lobate, free. Tail rudimentary. Head with a naked loral strip and bristly or variously lengthened feathers. Nostrils simple. Bill straight or decurved at end, compressed, acute … _Podicipidæ_. Feet three-toed, palmate. Hallux absent. Tail perfect. Head closely feathered or variously crested. Nostrils simple. Bill of indeterminate shape … _Alcidæ_. NORTH AMERICAN BIRDS. FAMILY TURDIDÆ.—THE THRUSHES. The _Turdidæ_, with the _Saxicolidæ_ and _Cinclidæ_, form a group closely related, by common characters, and appreciably different from the other _Oscines_ with slender bills and specially insectivorous habits, having, like them, ten primaries (the first much shorter than the second, but nearly always appreciable), and the nostrils uncovered. The great family of _Sylvicolidæ_, with similar characters of the bill, never present more than nine primaries. The most striking of these common characters is seen in the deeply cleft toes, of which the outer is united by the basal joint alone to the middle toe, while the inner is separated almost to the very base of its first joint.[21] The frontal feathers extend, with rare exceptions, to the very nostrils. The bill is elongated and subulate, moderately slender, and usually notched at tip; the culmen moderately curved from the base, and the mouth well provided with bristles, except in a few cases. Usually the scutellæ covering the front and sides of the tarsus are fused into one continuous plate, or else scarcely appreciable, except on the inner edge only; in the Mocking Thrushes they are, however, distinctly marked. The lateral toes are nearly equal, the outer rather the longer. With these as some of the principal characteristics, they may be distinguished from each other as follows:— NOTE.—In the present work the length of the tail is measured from the coccyx, inside of the skin, and not, as usually the case, from the base of the quills at their insertion. The wings are measured from the carpal joint, with dividers. A. Nostrils oval. Loral and frontal feathers with bristly points, or interspersed with bristles; rictus with longer or shorter bristles.