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Genus I.— COLYMBUS, Linn. DIVER. 



Bill as long as the head, straight, rather stout, much compressed, taper- 

 ing, 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, taper- 

 ing; oesophagus 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; cceca rather long and wide; cloaca globular. 



Vol. VII. 40 



