184 BULLETIN 50, UNITED STATES NATIONAL MUSEUM. 
erate to rather large, strongly curved, acute, that of the hallux 
decidedly shorter than the digit. 
Coloration.—Wings and tail (usually pileum also) cinnamon-rufous 
rest of upper parts plain brown; under parts plain pale brownish 
gray, light grayish brown, or dull buffy. Sexes alike. 
Range.—Costa Rica to Ecuadér (at least). (Many species.) 
KEY TO THE SPECIES OF ACRORCHILUS. 
a. Pileum, at least, rufous. (Adults.) 
b. Loral, orbital, auricular, and malar regions rufous; crown without black streaks 
(Acrorchilus erythrops.) 
c. Middle pair of rectrices russet-brown. (Ecuadér.) 
Acrorchilus erythrops erythrops (extralimital).6 
cc, Middle pair of rectrices bright cinnamon-rufous, like rest of tail. 
d. Rufous of head less extended, the occiput and nape brown, like back; chest 
and lower throat light buffy olive. (Costa Rica and Panamé4.) 
Acrorchilus erythrops rufigenis, adults (p. 185). 
dd. Rufous of head more extended, involving occiput and nape; chest mouse 
gray fading into nearly ash gray on throat. (Northwestern Colombia.) 
Acrorchilus erythrops griseigularis (extralimital).¢ 
6b. Loral, orbital, auricular, and malar regions buffy brownish, the superciliary 
region narrowly streaked with whitish; forehead and crown streaked with 
black. (Colombia to Ecuadér.)......Acrorchilus antisiensis (extralimital).¢@ 
aa. Pileum without rufous.......... Acrorchilus erythrops rufigenis, young (p. 185). 
ACRORCHILUS ERYTHROPS RUFIGENIS (Lawrence). 
LAWRENCE'S SPINETAIL. 
Similar to A. e. erythrops Sclater,¢ of Ecuadér, but middle pair of 
rectrices bright cinnamon-rufous (like other rectrices), instead of 
russet brown, cinnamon-rufous of head deeper and more extended 
(occupying whole of auricular and greater part of malar regions, as 
well as orbital, loral, superciliary, and supra-auricular regions as well 
as forehead and crown), general coloration darker, and size larger. 
@ On account of the very poor representation of species referred to the genus Siptornis, 
by Dr. Sclater and other recent authorities, in the material which I have been able to 
examine, I can not give a very definite statement of the number of species or extent of 
the geographic range of this genus, which is so exceedingly distinct, structurally, from 
Siptornis that it is difficult to imagine why the fact has not sooner been realized. The 
only species examined by me in this connection are the following: A. erythrops 
(Sclater), A. hellmayri (Bangs), and A. pallida (Maximilian). 
b Synallaxis erythrops Sclater, Proc. Zool. Soc. Lond., pt. xxviii, pt. i, May, 1860, 66 
(Pallatanga, w. Ecuadér; coll. P. L. Sclater). Siptornis erythrops Sclater, Cat. Birds 
Brit. Mus., xv, 1890, 60, part.—A[crorchilus] erythrops erythrops Ridgway, Proc. Biol. 
Soc. Wash., xxii, April 17, 1909, 72, in text. 
¢ Acrorchilus erythrops griseigularis Ridgway, Proc. Biol. Soc. Wash., xxii, April 17, 
1909, 72 (San Antonio, Rio Cali, n. w. Colombia; coll. E. A. and O. Bangs). 
4 Synallazis antisiensis Sclater, Proc. Zool. Soc. Lond., 1859, 457 (Cuenca, Ecuador; 
coll, P. L. Sclater).—Siptornis antisiensis Sclater, Cat. Birds Brit. Mus., xv, 1890, 59. 
¢ See Key to the Species, this page. 
