Myiarchus mexicanus.
1449
For an elaborate discussion of the various forms of this exceedingly difficult
genus, we are indebted to a recent monograph by Dr. Coues, in the Proceedings of the Philadelphia Academy, for June and July, 1872 (pp. 56-81). With the same material for our investigations, we have been led, after a very careful perusal of the valuable paper mentioned, and tedious critical comparison of the large material at our command, to adopt a somewhat difficult view of the relationship of the forms characterized. The following synopsis expresses their affinity as at present understood:—
Common Characters. Above olivaceous, usually uniform, sometimes darker, sometimes more ashy, on the head above. Head and jugulum more or less ashy, though the latter is sometimes very pale. Rest of lower parts sulphur-yellow, sometimes almost or quite white. Primaries, secondaries, and rectrices usually more or less edged on either web with rufous; but sometimes entirely destitute of this color.
Species and Varieties.
A. Bill sub-conical; sometimes nearly terete, its depth equal to, or exceeding, its breadth in the middle portion; its lateral outlines moderately divergent basally; terminal hook abrupt, strong. (Myionax.)
1. M. tyrannulus. No trace of rufous edgings on either wings or tail. Above ashy-olive, the pileum similar, the outer webs of wing-coverts and secondaries edged with whitish. Head, laterally and beneath, ashy, the throat and jugulum more whitish; rest of lower parts sulphur-yellow. Tail slightly rounded.
Pileum and nape umber-brown; upper surface umber-grayish. Bill dark brown. Wing, 3.50-3.70; tail, 3.60-3.90; culmen, .90-.95; tarsus, .80-.90. Hab. South and Central America, from Bolivia and Southern Brazil to Costa Rica … var. tyrannulus.[66]
Whole head and neck pure ash, paler on the throat, and darker on the pileum; upper surface greenish-ash. Bill black. Wing, 3.70; tail, 4.00; culmen, .82; tarsus, .91. Hab. Ecuador and Guayaquil … var. phæocephalus.[67]
2. M. validus.[68] All the wing-coverts, tertials, secondaries, primaries, and rectrices distinctly edged with rufous (the latter on both webs). Above olivaceous, more ashy anteriorly; the upper tail-coverts more rufescent; remiges broadly rufous on exterior edges; rectrices with the whole inner web (except a narrow streak along the shaft) and edge of outer web rufous. Head beneath, and entire throat and breast, deep ash; rest of lower parts sulphur-yellow, the junction of the two colors not well defined. Wing, 3.80-4.20; tail, 3.80-4.20; culmen, 1.00; tarsus, .80-91; tail even; third and fourth quill longest. Hab. Jamaica.