1916] Chandler: Structure of Feathers 303 
is over half the length of the main feather plate, with 30 or more 
barbs in the breast feathers. 
a) Diomedea exsulans 
(1) Remex 
Highly specialized as functional flight feather, the barbules im 
fact possessing more ‘‘frills’’ than in any other feather known. 
Shaft deeper than wide, especially on more proximal portion of 
feather, with sharp, inconspicuous groove; calamus large and in- 
flated. Vanes firm and elastic; barbs fairly close together, about 
18 per centimeter on inner vane, somewhat less on outer, their rami 
considerably deepened near junction with shaft, and barbules firmly 
interlocking. Pith of barbs consisting of only a single layer of 
hollow cells transversely, the ventral ridge not as broad and thin 
as in loons, but constituting about a fourth of depth of barb. 
Inner vane——Distal barbules (pl. 17, fig. 10a) with a number 
of rather striking characteristics. Twist between base and pennu- 
lum unusually pronounced, making a very sharp curve in dorsal 
contour of barbules as they lie undisturbed in vanule. Base large 
and rather long, 0.45 mm. by 0.16 mm., differing from barbs of 
birds of any other group, as far as known, by the presence of one 
or two minute forward-projecting prongs on dorsal edge, on cells 
bearing ventral teeth. Latter very peculiar in form, not simple 
finger-like or lobate projections, but bifid at tip, and often trifid 
(pl. 17, fig. 10a). Pennulum longer than base; hooklets moderate 
and well-formed; ventral cilia long, slender and flexible; the dorsal 
cilia with much the same character as in Colymbiformes, i. e., short 
and triangular basally, then becoming more slender, and finally de- 
creasing, those beyond the sixth usually rudimentary or absent en- 
tirely. Proximal barbules (pl. 17, fig. 10b) large and well formed; 
base very long and relatively slender; about 0.76 mm. by 0.06 
mm. with a well-developed flange, and rather small dorsal spines; 
ventral teeth differing from those of all other birds in being slender, 
flexible, and greatly elongated, sometimes 0.15 mm. long, and 
usually with wavy appearance, as shown in figure. Pennulum ap- 
proximately equal to base in length, broad at proximal end (about 
0.01 mm.), tapering gradually to tip. Distal barbules set very 
close together, about 30 per millimeter, proximals, being set at a 
much more acute angle, much less numerous, about 17 per milli- 
meter. 
Outer vane—Distal barbules (pl. 17, fig. 10c) differing from 
those of inner vane in same manner as in loons, 1. e., base slightly 
more elongate, hooklet region of pennulum broader, hooklets more 
numerous, ventral cilia longer and more filamentous, and dorsal 
cilia undeveloped except terminally, but specific characteristics, 
such as dorsal prongs and jagged ventral teeth, unchanged. Pro.c- 
imal barbules (pl. 17, fig. 10d) with shorter and more tapering 
base, and extremely long, heavy pennulum with a complete series 
of ventral barbicels, the more proximal of which long and wavy, 
