_Helminthophaga luciæ_, COOPER, Pr. Cal. Acad. July, 1861, 120 (Fort Mohave).—BAIRD, Rev. Am. B. 1864, 178.—ELLIOT, Illust. Birds N. Am. I, v.—COOPER, Orn. Cal. 1, 1870, 84. SP. CHAR. General form and size that of _H. ruficapilla_. Above light-cinereous; beneath white, having a soiled, very pale buff, almost white tinge on the throat, breast, and flanks. A patch on the vertex, as in _H. ruficapilla_, and the upper tail-coverts, dark chestnut-brown. Lores to nostrils and region round the eye, like the throat, in rather decided contrast to the ash of the crown. Quills and tail-feathers brown, narrowly edged externally with gray. An obsolete terminal white patch on the inner web of the outer feather; this web in most of the other tail-feathers likewise narrowly edged with white. Axillars and inner face of wings white. Iris brown. Tarsi blue. Length, in life, 4.40; extent, 6.90; wing, 2.40. Length of skin, 3.90; wing, 2.33; tail, 1.86; tarsus, .64; middle toe and claw, .50; bill above, .35; gape, .50. HAB. Fort Mohave, Colorado River (Middle Province of United States); Fort Whipple, Arizona. HABITS. This is also a new or recently discovered species of this interesting group of Warblers. In regard to its nest and eggs nothing is positively ascertained, yet as all the birds of this genus are known to build on the ground, and to have a great uniformity in the characteristics of their eggs, it seems to be a matter of natural inference that this species also is a ground builder, and has eggs similar to those of the Nashville Warbler. For the little we know in regard to its habits and distribution, we are indebted to the observations of Dr. J. G. Cooper of California, who first discovered it, and to Dr. Coues, who has since met with it in Arizona. Dr. Cooper first observed this species near Fort Mohave, where it made its appearance about the last of March. His attention was called to it by its peculiar notes, resembling those of some _Dendroicæ_, but fainter. After considerable watching and scrambling through dense mezquite thickets in its pursuit, he succeeded in shooting one, and found it to be a new species. Afterwards they became more numerous, frequenting the tops of the mezquite-trees in pursuit of insects, and constantly uttering their short but pleasing notes. About ten days after the first appearance of the males, Dr. Cooper obtained the first female, and thinks that without doubt they are much later in their migrations, as is the case with other Warblers. He was not able to discover their nest, having to leave the valley late in May. Mr. Holden obtained other specimens of this bird, near the 34th parallel, in March of 1863. Dr. Coues met with three individuals of this species near Fort Whipple, where it is a summer resident. It arrives there between the 15th and the 20th of April, and remains until the latter part of September. It mates about the last of April, and the young birds appear early in June.