Bill of the length of the head, straight, rather stout, much
compressed, pointed; upper mandible with the dorsal line declinate,
almost straight, or towards the end convex; nasal groove rather long,
feathered at the base. Nostrils basal, linear, direct, pervious. Feet
stout, short, placed extremely far behind; tarsus extremely
compressed; toes four, the first very small, and lobed; the anterior
united by webs, which in some are lobed. Plumage dense, short,
glossy, generally silky beneath. Wings small, very narrow, acute. Tail
very short, sometimes extremely small, and forming a slight tuft.
Tongue slender, trigonal, tapering; œsophagus very wide in its
whole length, or narrowed in the anterior part with the proventriculus
wide; stomach generally large, muscular, with a dense rugous
epithelium; intestine rather long and wide; as are the cœca; cloaca
globular.
GENUS I. COLYMBUS, Linn. DIVER.
Bill as long as the head, straight, rather stout, much compressed,
tapering, pointed; upper mandible with the dorsal line descending, and
slightly convex towards the end, the ridge convex, narrowed towards
the point, the sides nearly erect, convex, the edges sharp and
considerably inflected; the tip narrow; nasal groove rather long,
feathered at the base. Nostrils basal, linear, direct, pervious; lower
mandible with the angle extremely narrow and extending beyond the
middle, the dorsal line straight and sloping towards the point, the
ridge convex and narrow, the edges sharp and involute, the tip
attenuated. Head of moderate size or rather large, oblong, narrowed
before; neck rather long and thick; body elongated, much depressed.
Feet short, rather large, placed very far back; tibia almost entirely
concealed; tarsus short, exceedingly compressed, sharp-edged before
and behind, covered all over with reticulated scales; toes four, hind
toe extremely small, connected with the second by a very small
membrane; anterior toes united by entire membranes, the outer longest,
the third a little shorter, all scutellate. Claws very small,
depressed, blunt. Plumage short and dense, the feathers in general
oblong. Wings very small and narrow, curved, first quill longest,
secondaries broad and rounded. Tail extremely short, rounded of more
than twelve feathers. Tongue long, trigonal, tapering; œsophagus
very wide; proventriculus extremely dilated; stomach rather large,
roundish, a little compressed, moderately muscular, with a rather
thick, dense, longitudinally rugous epithelium; intestine rather long
and wide; cœca rather long and wide; cloaca globular.