My friend Captain JAMES CLARK ROSS, of the Royal Navy of England, once placed at my disposal a specimen of the Loon procured in a very high latitude, and which, having closely inspected it, I found to differ from the one represented in the plate, only in having the point of the bill slightly elevated or recurved, and of a fine yellow tint. Dr RICHARDSON informed me that, on one of his arduous northern journeys, he saw a very large and handsomely crested Diver, which, although somewhat prematurely, I propose honouring with the name of _Colymbus Richardsoni_. COLYMBUS GLACIALIS, _Linn._ Syst. Nat. vol. i. p. 221. Adult.—_Lath._ Ind. Ornith. p. 799. COLYMBUS IMMER, _Linn._ Syst. Nat. vol. i. p. 222. Young.—_Lath._ Ind. Ornith. p. 800. COLYMBUS GLACIALIS, _Ch. Bonaparte_, Synopsis of Birds of United States, p. 420. GREAT NORTHERN DIVER or LOON, _Wils._ Amer. Ornith. vol. ix. pl. 74, fig. 3. COLYMBUS GLACIALIS, _Richards. and Swains._ Fauna Bor. Amer. vol. ii. p. 474. LOON, or GREAT NORTHERN DIVER, _Nuttall_, Manual, vol. ii. p. 513. Adult Male. Plate CCCVI. Fig. 1. Bill as long as the head, straight, stout, much compressed, tapering to a point. Upper mandible with the dorsal line descending and slightly convex towards the end, the ridge convex, narrowed towards the point, the sides convex beyond the nostrils, the edges sharp and considerably inflected, the tip narrow and sharpish. Nasal groove short, nostrils basal, linear, direct, pervious. Lower mandible with the angle extremely narrow, and extending beyond the middle, the dorsal line straight and sloping upwards to the point, the ridge convex and narrow, the edges sharp and involute; the tip attenuated. Head of moderate size, oblong, narrowed before. Neck rather long and thick. Eyes of moderate size. Body elongated, much depressed, of an elliptical form viewed from above. Wings small. 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 angular scales; hind toe extremely small, connected with the second by a very small membrane; the anterior toes united by articulated membranes, the fourth or outer longest, the third a little shorter, the second considerably shorter than the third, all covered above with very numerous narrow scutella, the second toe with a free two-lobed membrane; claws very small, depressed, blunt. Plumage short and dense; of the head and neck very short, and blended; of the lower parts blended, short, with slight gloss; of the upper compact, glossy; the feathers in general oblong, those of the upper parts with the extremity abrupt. Wings proportionally very small and narrow, curved; primaries strong, tapering, the first longest, the second almost as long, the rest rapidly graduated; secondaries broad, and rounded. Tail extremely short, rounded, of twenty feathers.