The American _Motacillidæ_ are distinguished from the _Sylvicolidæ_ by the emargination of the outer and the great elongation of the inner secondaries, as well as by other features referred to under that family. _Anthus_, in particular, differs in the lengthened and slightly curved hind claw. There is little difficulty in distinguishing the _Sylvicolidæ_, however, from any families excepting the slender-billed forms of the _Tanagridæ_, as _Chlorospingus_, _Nemosia_, _Chlorochrysa_, etc., and the conirostral _Cœrebidæ_. In fact, some ornithologists are inclined to include all three of the families thus mentioned in one, from the difficulty of marking their boundaries respectively. In fact, we are of the opinion that no violence would be done by adopting this view, and would even include with the above-mentioned families the _Fringillidæ_ also. The order of their relation to one another would be thus: _Fringillidæ, Tanagridæ, Sylvicolidæ, Cœrebidæ_; there being scarcely any break in the transition between the two extremes, unless there are many genera referred to the wrong family, as seems very likely to be the case with many included in the _Tanagridæ_. The _fringilline_ forms of the latter family are such genera as _Buarremon_ and _Arremon_, they being so closely related to some _fringilline_ genera by so many features—as rounded concave wing, lax plumage, and spizine coloration—as to be scarcely separable. Either these two families are connected so perfectly by intermediate forms as to be inseparable, or the term _Tanagridæ_ covers too great a diversity of forms. With the same regularity that we proceed from the _Fringillidæ_ to the typical forms of the _Tanagridæ_ (_Pyranga_, _Tanagra_, _Calliste_, etc.), we pass down the scale from these to the _Sylvicolidæ_; while between many genera of the latter family, and others referred to the _Cærebidæ_, no difference in external anatomy can be discovered, much less expressed in a description. In the following synopsis we attempt to define the higher groups of the _Sylvicolidæ_, although in the large number of species and their close relationships it is very difficult to express clearly their distinctive features. Subfamilies. A. Bill conical, its bristles very weak, or wanting. _a._ Bill sub-conical, the culmen and commissure nearly straight. Sylvicolinæ. Feet weak, not reaching near the end of the tail. Wing pointed, considerably longer than the nearly even or slightly emarginated tail. Feet dark-colored (except in _Helmitherus_, _Helinaia_, and _Parula_). _Arboreal._ Geothlypinæ. Feet strong, reaching nearly to end of the tail. Wing rounded. Feet pinkish-white. _Terrestrial._ _b._ Bill high and compressed, the culmen and commissure much curved. Icterianæ. Bill without notch or rictal bristles; wing much rounded, shorter than the tail. B. Bill depressed, its bristles strong.