M. PYGOPODES. Feet palmate or lobate. Tibiæ feathered, often with a long apophysis, always buried in common integument nearly to the heel-joint, necessitating a more or less erect posture of the body on land, where progression is difficult. Hallux small, elevated or wanting; feet lobate or palmate. Bill of indeterminate shape, wholly corneous, never lamellate or serrate, nor with gular pouch. Nostrils not abortive. Wings very short, reaching scarcely or not to the base, never to the tip, of the short, sometimes rudimentary, tail. Palate schizognathous. Carotid usually double, sometimes single (in _Podiceps_ and _Mergulus_). Nature altricial or præcocial; young ptilopædic. Highly natatorial. N. SPHENISCI. With general characters of the last group, but distinguished by unique ptilosis and wing-structure, etc. Plumage without apteria, of singularly modified scale-like feathers on most parts; no developed remiges. Wings unfit for flight, insusceptible of perfect flexion or extension, very short, with peculiarly flattened bones and stable articulations. Skeleton non-pneumatic. Many bones, terete in ordinary birds, here flattened. Metatarsal bone flattened transversely, doubly fenestrate. Hallux elevated, lateral, minute, free. No free pollex. Two anconal sesamoids; patella from double centres; tibia without apophysis; a free tarsal ossicle. Sternum with long lateral apophyses. Pelvic connections unstable. Carotids double. Comprising only the Penguins. Confined to the Southern Hemisphere. Having thus presented and defined an arrangement of the higher groups into which recent Carinate birds are susceptible of division, I next proceed to the consideration of the North American Families of birds which the authors of the present work have provisionally adopted as suitable to the end they had in view. Professor Baird urges the caution that the scheme is intended merely for the convenient determination of the North American species, aware that in many instances diagnoses or antitheses of entire pertinence in such application would fail or be negatived by consideration of the exotic forms. The arrangement of the families here adopted is essentially that presented in 1858 in Professor Baird’s “Birds of North America,” modified somewhat in accordance with more recent views of Professor Sundevall and others. But before proceeding to the analysis of the families, I will introduce an artificial clew to the preceding higher groups as adopted, so far as they are represented by North American species. ARTIFICIAL KEY TO THE FOREGOING HIGHER GROUPS, _By means of which any North American bird may be readily referred to that group to which it is held to belong._ I. Toes 3; 2 in front, 1 behind (_Pici_) PICARIÆ.