300 University of California Publications in Zoology Vou. 138 
with single, slender ventral tooth, the latter with 3 or 4 short hook- 
lets, and a series of curved ventral barbicels. Type same as that 
in Aechmophorus occidentalis (pl. 16, fig. 9e). Proximals with 
slender, elongate base, and slender pennulum, the latter with a 
series of moderate ventral barbicels. See plate 16, figure 9f (Aech- 
mophorus occidentalis). On distal portion of feather, both distal 
and proximal barbules reduced to single elongate type, resembling 
somewhat proximal barbules of penguins; no sharp demarcation be- 
tween base and pennulum, but latter with a series of curved ventral 
barbicels; base, on some of terminal barbules, with one or two flex- 
ules developed (pl. 16, fig. 99g, of Aechmophorus occidentalis), a 
highly significant fact considering their universal occurrence in 
Procellariiformes. 
Breast feathers well-developed, with fairly strong vanes. Bar- 
bules remarkably similar to those of penguins; distals (pl. 16, 
fig. 8e) with narrow base and weak ventral teeth, pennulum with 
long series of short hooklets, gradually changing to curved ventral 
cilia, exactly as in penguins; proximal barbules towards tip of 
barbs (pl. 16, fig. 8f) with slender tapering base and barbicelled 
pennulum, the ventral cilia longer than dorsal, but both series 
present. 
b) Other Types 
Gaviidae—Gavia pacifica has practically identically the same 
structure as the species above described. 
Colymbidae—In Aechmophorus occidentalis the structure of 
the remiges is strikingly similar to that of Gavia, differmg only in 
a few details. The rami are not so deep and have not so wide a 
ventral ridge as in the Gaviidae, and they are set closer on the 
shaft, there being about 25 and 28 per millimeter on the imner and 
outer vanes respectively. The barbules are essentially the same in 
structure as in Gavia, but, as would be expected on smaller feath- 
ers, they also are smaller; the distals (pl. 16, figs. 9a, 9c), for ex- 
ample, are only about 0.47 mm. long, the base constituting about 
half of this. On the proximal barbules of the inner vane (pl. 16, 
fig. 9b) the base is relatively longer and narrower, with less con- 
spicuous ventral teeth, while in the proximals of the outer vane 
(pl. 16, fig. 9d) the barbicels are much smaller and weaker. Colymbus 
holboelli and Podilymbus podiceps are similar, but the barbicels of 
the proximal barbules of the outer vane are still less conspicuously 
developed, and confined to barbules on a less extensive portion of 
the barb. 
The back feathers of Aechmophorus occidentalis closely resemble 
those of the loons. In most other grebes, however, e. g. the various 
species of Colymbus and Podilymbus, a hairlike effect is produced in 
