The eggs, which are sometimes two, more frequently three, average three inches in length, by two in their greatest breadth, which is about a third of the whole length distant from the extremity. Their form is that of the Red-throated Diver, which however they exceed in size. The shell is rather thick, the surface roughish, the ground colour chocolate tinged with olive, sparingly spotted at the larger end with very dark umber and black, and sprinkled all over with very small dots of the same colour. I have represented an adult male, a female, and a young bird. COLYMBUS ARCTICUS, _Linn._ Syst. Nat. vol. i. p. 221.—_Lath._ Ind. Ornith. vol. ii. p. 800.—_Ch. Bonaparte_, Synopsis of Birds of United States, p. 420. COLYMBUS ARCTICUS, BLACK-THROATED DIVER, _Richards. and Swains._ Fauna Boreali-Americana, vol. ii. p. 475. BLACK-THROATED DIVER, _Nuttall_, Manual, vol. ii. Adult Male. Plate CCCXLVI. Fig. 1. Bill as long as the head, straight, stout, higher than broad at the base, much compressed toward the end, and tapering to a point. Upper mandible with the dorsal line descending and considerably convex toward the end, the ridge convex, narrowed toward the point, the sides convex beyond the nostrils, the edges involute for half their length in the middle, direct at the base and toward the end, the tip narrow and sharpish. Nasal groove rather long and narrowed; nostrils sub-basal, linear, direct, pervious. Lower mandible with the angle extremely narrow, and very long, the dorsal line ascending and very slightly convex, 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, externally marginate, connected with the second for half its length by a membrane, which extends, narrowing, to the end; the anterior toes connected by articulated membranes, the fourth or outer longest, the third a little shorter, the second considerably shorter than the third; all covered above with numerous narrow scutella; the second toe with a free two-lobed membrane, the claws very small, depressed, blunt.