A specimen of this little Flycatcher was sent to me along with the one last described, by Mr. BAIRD, and I have found his description of it so correct that I shall give it below. Mr. BAIRD says:

"This species was first observed and procured in May 1839, near Carlisle, Pennsylvania. Since then numbers have been observed and shot on every succeeding spring. Like the preceding, (T. flaviventris,) this bird does not frequent deep forests, but is found among the scattering trees which border our streams. It is rather shyer than T. flaviventris, and does not, like that species, seek dense thickets. It also, most probably, goes further north to breed, as after the last of May it is no longer to be seen. It visits us from the south in the latter part of April, generally making its appearance about a week before T. flaviventris."

This Flycatcher has a great range through the countries bordering upon the Upper Missouri. Several specimens were procured by some of my companions, and I not unfrequently met with them in my rambles along the sides of small though interesting valleys in the ravines so numerous about the Yellow Stone river and Fort Union. In its habits it resembles the smaller species allied to itself, all of which have been already described. I have no doubt that it breeds in the sections of the country where I saw it, but its nest escaped our utmost endeavours to discover it.

LEAST FLYCATCHER, Tyrannula minima, Baird.

5 inches 2 lines, 8 inches 3 lines.

Mountains of Pennsylvania. Shores of the Missouri. Probably ranges over all the Middle and Western Districts.


Male.

"Body rather slender. Bill smaller than the other species of the genus. Tarsus slightly longer than the middle toe. Second primary longest, third nearly equal, and rather longer than fourth, fifth one line shorter than fourth, first intermediate between fifth and sixth. Tail emarginate and slightly rounded.

"Colour. Bill dark blackish-brown above, pale born colour beneath. Feet black. Plumage of the upper parts dark greyish-olive, crown somewhat darker, rump lighter and inclining to greyish. A narrow ring round the eye greyish-white. Fore part of breast, sides, and sides of the neck light ash-grey, middle of throat white, rest of the lower parts very pale yellow or yellowish-white. Primaries and tail feathers wood-brown, the former narrowly, and the latter broadly edged with olive. Lower row of lesser wing coverts and the secondary coverts darker, tipped with dirty-white, that colour forming two bands across the wings. Secondaries also dark, like the greater wing coverts, and broadly edged with yellowish-white.

"Length 5 inches 2 lines. Extent 8 inches 3 lines. Folded wing 2 1/2 inches.

"No perceptible difference as to colour or size between the sexes.

"Observations. This species will be recognized by its size, its slender form making it the smallest of our North American Tyrannulae. In colour it most resembles T. Traillii of Aud., but it is a much smaller bird, being nearly three-fourths of an inch shorter. T. Traillii has the breast and sides of the neck olivaceous; in this species light ash-grey; the tail also of T. Traillii is even.

"It differs from T. pusilla (comparing with the description of SWAINSON and RICHARDSON as before) in having the wings more pointed, the second and third primaries being longest, and the first longer than the sixth; while in pusilla the third and fourth are longest, and the first shorter than the sixth. The upper tail coverts of pusilla are uniform in colour with the back; in our species lighter; pusilla has the front "hoary;" in this species dark. The lower parts of pusilla are pale sulphur-yellow, "approaching to siskin-green;" in our species yellowish-white; the under mandible of pusilla is yellowish-brown; of this species horn-colour. From the figure in the Fauna Boreali-Americana, pusilla appears to be a stouter bird, much deeper in colour beneath and having a broader bill. Its smaller size, and darker colour above, will distinguish it from T. acadica (being two-thirds of an inch shorter), which species has also longer and more pointed wings, a much larger bill, which is light brown beneath, and an even tail.