Neither Dr. Gambel nor Dr. Heermann found this species in California excepting during the winter, and were of the opinion that none remain there to breed. Dr. Kennerly observed them at different points among the Rocky Mountains, where they frequented the vicinity of his camp early in the morning, at some times in pairs and at others in flocks of four or five. Mr. J. K. Lord states that he found this Bluebird very abundant between the Cascades and the Rocky Mountains, where they arrive in June and leave in September. After nesting they assembled in large flocks, and fed on the open plains. The eggs are of a very light blue, paler than those of the other species. They measure .89 of an inch in length by .66 in breadth. Mr. Ridgway states that he found the Rocky Mountain Bluebird nesting in Virginia City in June. Its nests were built about the old buildings, and occasionally in the unused excavations about the mines. At Austin he also found it common in July, in similar localities. On the East Humboldt Mountains it was very numerous, especially on the more elevated portions, where it nested among the rocks and, though more rarely, in the deserted excavations of woodpeckers in the stunted piñon and cedar trees. He describes it as generally very shy and difficult to obtain, seldom permitting a very near approach. In its habits it is much less arboreal than either _S. mexicana_ or _S. sialis_, always preferring the open mountain portions in the higher ranges of the Great Basin. In regard to its notes Mr. Ridgway says: “The common note of this species would, from its character, be at once recognized as that of a Bluebird. Its autumnal note, however, lacks entirely the peculiar plaintiveness so characteristic of that of our Eastern species, and is much more feeble, consisting of a simple weak _chirp_. Like the _S. mexicana_, the _S. arctica_ was also never heard to give utterance to anything resembling the lovely spring warbling of the _S. sialis_.” FAMILY SYLVIIDÆ.—THE SYLVIAS. CHAR. Bill much shorter than head, slender, broad, and depressed at the base, distinctly notched and decurved at the tip. Culmen sharp-ridged at base. Frontal feathers reaching to the nostrils, which are oval, with membrane above, and overhung—not concealed—by a few bristles or by a feather. Rictal bristles extending beyond nostrils. Tarsi booted or scutellate. Basal joint of middle toe attached its whole length externally, half-way internally. Primaries ten; spurious primary about half the second, which is shorter than the seventh. Lateral toes equal.