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_.