The nests measure about 4 inches in diameter and 2¾ in height. The cavity is 2 inches deep, and its diameter 2½ inches. They are unusually compact for the nest of a thrush, and are composed chiefly of an elaborate interweaving of fine sedges, leaves, stems of the more delicate _Equisetaceæ_, dry grasses, strips of fine bark, and decayed leaves, the whole intermingled with the paniculated inflorescence of grasses. There is little or no lining other than these materials. These nests were all found, with but few exceptions, on the branches of low trees, from two to seven feet from the ground. In a few exceptional cases the nests were built on the ground. Occasionally nests of this species are found constructed with the base and sides of solid mud, as with the common Robin (_Turdus migratorius_). In these, as also in some other cases, their nests are usually found on or near the ground. So far as I am aware neither its occasional position on the ground, nor its mud frames, are peculiarities ever noticeable in nests of _T. swainsoni_. The eggs were usually four in number. Their color is either a deep green tint, or green slightly tinged with blue; and they are marked with spots of russet and yellowish-brown, varying both in size and frequency. Their mean length is .92 of an inch, and their mean breadth .64. The maximum length is .94 and the minimum .88 of an inch. There is apparently a constant variation from the eggs of the _T. swainsoni_; those of the _aliciæ_ having a more distinctly blue ground color. The nests are also quite different in their appearance and style of structure. The _Hypnum_ mosses, so marked a feature in the nests of _T. swainsoni_, as also in those of _T. ustulatus_, are wholly wanting in those of _T. aliciæ_. This bird and the robin are the only species of our thrushes that cross the Arctic Circle to any distance, or reach the shore of the Arctic Ocean. It occurs from Labrador, all round the American coast, to the Aleutian Islands, everywhere bearing its specific character as indicated above. It is extremely abundant on and near the Arctic coast, between the mouth of the Mackenzie River and the Coppermine, more than 200 specimens (mostly with their eggs) having been sent thence to the Smithsonian Institution by Mr. MacFarlane. In all this number there was not a single bird that had any approach to the characters of _T. swainsoni_, as just given. From the Slave Lake region, on the other hand, _T. swainsoni_ was received in nearly the same abundance, and unmixed during the breeding season with _T. aliciæ_. Turdus swainsoni, CABANIS. OLIVE-BACKED THRUSH; SWAINSON’S THRUSH.