NATURAL SCIENCES OF PHILADELPHIA. 
887 
variations to be as follows. The difference in total length of body is rather 
more than -50 of an inch. The average size is rather less than 5-50 inches. 
The difference in length of wing from the carpal joint is somewhat over -25 
of an inch. In length of tail the differences are about the same. The feet are 
constant, both absolutely and relatively, the variations being scarcely appre- 
ciable. The claws, however, vary quite notably in length and amount of cur- 
vature. To express the difference in the feet of this species and the A. Una - 
rius, relatively without measurement, we have said that in the former the tar- 
sus exceeds the middle toe and claw, and that in the latter the toes are 
equal ; but this variation in the size of the claws may cause the fact not to hold 
good in all cases. The bills vary quite notably in size and color, they being 
sometimes nearly as bright yellow as in Unarms ; but they are usually almost 
entirely dusky, and they are never so acutely pointed and so much compressed 
as in that species, preserving their regular conical shape without much varia- 
tion. The plumuli vary in color, from dingy whitish to dusky, but are usually 
of the former color, and are always heavy and full. The upper parts are 
usually as given in the description ; lighter than in Unarms , the conspicuous 
yellowish or buff of that species fading into whitish more or less pure. Some- 
times, however, the upper parts are quite like Unarms ; in other specimens 
the dusky centres of the feathers become so broad and conspicuous as to 
give the prevailing color of the upper parts, causing the specimens to approach 
A. fuscescens in this respect only. In these cases, however, the light edges of 
the feathers, though so narrow, are nearly pure white, and the rump is very 
broadly pure white, entirely without streaks, forming a marked contrast. 
The edgings of the wings and tail do not vary notably, being always nearly 
identical with those of linarius , but perhaps a little purer. The rump in adult 
birds is pure white, with a rosy tinge, without spots or streaks ; but in imma- 
ture specimens it is frequently marked with dusky, though never so thickly as 
in linarius . The dusky streaks on the sides are usually very sparse, and 
though varying in number and intensity, never become so thick and dark as in 
linarius. These streaks in immature and female birds frequently extend as 
slight touches quite across the breast. In adult males the breast is immacu- 
late, with a light rosy tint. In the fullest plumaged males the rosy is always 
several shades lighter than in the males of linarius of the same age. 
Comparison with allied species , — A. linarius being most closely related, in the 
foregoing descriptions the comparisons have been made with that species. 
The points of difference may be summed up as follows : The smaller, more 
conic, less compressed, darker colored bill, with its very heavy and dense 
nasal plumuli ; the different character of the streaks above ; the white imma- 
culate rump; the paucity of the streaks on the sides; the much lighter rosy 
tinge of the breast and abdomen ; the smaller, every way weaker feet, with 
their much shorter toes. 
Some specimens — the largest and lightest colored — resemble A. canescens in 
general appearance, having the same conic bill, heavy plumuli, white rumps, 
sparsely streaked sides, &c. They may, however, be readily distinguished by 
the great discrepancy in the size of the feet and claws, those parts in canes- 
cens being as much larger and stronger in linarius as they are smaller and 
weaker than in that species in exilipes. 
The species requires no comparison with A. fuscescens, still less so with A. 
rostratus , the differences from both of those species being sufficiently obvious. 
The very large, bright yellow bill, with the short plumuli of A. IlolbtiUi , 
at once separates that species. The smaller size, more acute bill, less dense 
plumuli, general rufous tinge and shorter tail of A. rufescens will serve to dis- 
tinguish it. Both these species, moreover, have the same character of feet as 
has the A. linarius. 
Discussion of synonymy. — The only name which we have met with which can 
be referred to this species, is the Fringilla , or Idharia borealis Temm., of Aw~ 
1861 .] 
