The literature contains descriptions of several warblers not recognized as established species by the A. O. U. Check-List (1931). Some, described and illustrated by older writers such as Wilson and Audubon, cannot be identified; others are presumably hybrids; and one, _Sylvia autumnalis_ Wilson, the autumn warbler, is clearly the black-poll in fall plumage. The first category includes _Dendroica carbonata_ (Audubon), the carbonated warbler, of which the Check-List says "the published plates may have been based to some extent on memory"; _D. montana_ (Wilson), the blue mountain warbler, which is "known only from the plates of Audubon and Wilson"; and _Wilsonia_ (?) _microcephala_ (Ridgway), the small-headed flycatcher, of which it says: "Known only from the works of Wilson and Audubon whose specimens came from New Jersey and Kentucky respectively. There is some question whether they represent the same species." In the second category is _Vermivora cincinnatiensis_ (Langdon), the Cincinnati warbler, described in 1880. "The unique type is regarded as a hybrid between _Vermivora pinus_ (Linnaeus) and _Oporornis formosa_ (Wilson)." Recently, in a letter dated August 3, 1948, Dr. George M. Sutton reports to Mr. Bent the discovery of a second Cincinnati warbler, taken in Michigan on May 28, 1948. He says: "Its bill and feet are large for _Vermivora_ and its under tail coverts proportionately too long for that genus. It has only a faint suggestion of wing-barring and the merest shadow of a pattern on the outer rectrices. One of its most interesting and beautiful characters is the gray tipping of the feathers at the rear of the crown, as in _O. formosus_. The effect is very unusual, for the gray-tipped feathers are yellow. It is, in short, obviously a cross between _Vermivora_ and _Oporornis_." The status of _Vermivora leucobronchialis_ and _V. lawrencii_ and the relationship between them puzzled ornithologists for upward of two generations. William Brewster (1876) described the former as a new species, and since that time, as Walter Faxon (1911) writes, "almost every conceivable hypothesis has been advanced by one writer or another to fix its true status in our bird-fauna." In addition to being considered a valid species, it has been regarded as a hybrid (Brewster, 1881), as a dichromatic phase, that is, a leucochroic phase of _V. pinus_ (Ridgway, 1887), as a mutant (Scott, 1905), and finally as a phase, "ancestral in character" (atavistic) of the goldenwing (C. W. Townsend, 1908).