54 SYLVITIDA. 
The bird, a male, was found in scrubby wood near the roadside. The following year 
Mr. Owen obtained a female bird with its nest and eggs in the same locality. The 
nest, a very neat compact structure, was composed outwardly of dried stalks of grass 
and roots, with a coating of cobweb and other adhesive materials. ‘The lining consisted 
of the feathery parts of seeds, horsehair, and fine grass; the whole structure measured 
13 inch across the inside and 13 inch in depth. ‘This nest was situated in low 
brushwood, almost under the eaves of one of the ranchos. ‘The eggs are white, spotted 
with red, principally of two shades, the spots increasing in number towards the obtuse 
end; they measure—axis 0°6, diam. 0°45 in. 
Besides these typical birds, the male of which has the lores white, but no white 
supercilium, though a few white feathers are to be seen in this region in the type 
specimen, we have seen similar ones from the Isthmus of Tehuantepec, where Prof. 
Sumichrast observed them in May and December. 
Having thus given some account of the three forms of black-headed Polioptilw found 
in Central America (P. nigriceps with the lores wholly black, P. albiloris with the lores 
white, and P. dilineata with both lores and superciliaries white), it remains to consider 
the position of certain specimens which seem to have intermediate characters connecting 
two or all of these forms together. These birds were obtained, with a female of the 
true P. bilineata, near La Union in San Salvador, and have the lores black, with a 
few white feathers intermingled. They were once attributed by us to P. buffoni—that 
is, the Colombian bird we now consider to be the same as P. nigriceps; and they are 
undoubtedly as closely allied as possible to that bird; Prof. Baird, however, preferred 
to call some of them P. albiloris. Putting P. albiloris aside, and observing the ditribu- 
tion of P. nigriceps and P. bilineata, we find the curious fact that the ranges of these 
two forms actually cross one another, and that the area where P. bclineata comes into 
contact with the northern section of P. nigriceps corresponds more or less to that occupied 
by P. albiloris, at once suggesting the supposition that P. aldiloris is not a true species 
at all, but due to the intermingling of P. bilineata with P. nigriceps, and, further, that 
technically these last-named birds are not true species either. The way the present 
state of affairs has come about may have been as follows :—Formerly P. nigriceps was 
the only form which was found from Colombia to Mazatlan. The form of Western 
Ecuador, P. bilineata, then began to spread, pushed out or more probably absorbed 
P. nigriceps in Panama and Costa Rica, where now only pure-blooded P. bilineata are 
found. In San Salvador and Central and Western Guatemala to the Isthmus of Tehu- 
antepec the process of absorption is still incomplete; and hence the presence of the 
intermediate forms represented by P. albiloris. But P. bilineata has done more than 
this; for in Vera Paz we find pure-blooded birds, showing that it has established itself 
beyond the influence of P. nigriceps. The range of this last form has thus been com- 
pletely severed, one part remaining in Colombia and the other in Western Mexico. 
