306 University of California Publications in Zoology (Vou. 18 
In Oceanodroma and Pelecanoides the barbules are slightly 
shorter, usually 0.8 to 0.9 mm. long, and have very small prongs, 
not noticeably larger near the base of the barbules than at the tip. 
The black pigment in the case of Oceanodroma melania is evenly 
distributed in the barbules, or almost so. 
d) Relationships 
The Procellariiformes, in the structure of their feathers, show 
unmistakable resemblances to the Colymbiformes, especially the 
loons, so much so that their close relationship can hardly be doubted. 
They show, however, a considerably higher degree of development 
than do the Colymbiformes, the barbules of both remiges and body 
feathers possessing all the ordinary types of barbicels in highly 
developed form, as well as some special structures of their own. 
The bifurcated ventral teeth, dorsal prongs on the base in the 
distal barbules of the remiges, and the elongated, delicate, wavy 
ventral teeth of the proximals, are characters belonging solely to 
Procellariiformes, or at least reach their highest development there. 
The fiexules of the body feathers also reach their highest develop- 
ment in these birds. In view of these facts, we must look upon the 
Procellariiformes, at least the more specialized ones, such as Dio- 
medea, as representing the end of a path of evolution of their own, 
while a more primitive procellariiform bird probably gave rise to 
the Ciconiiformes through the Steganopodes (see page 315). 
e) Summary 
Procellariiformes may be characterized as follows: 
(1) Plumules evenly distributed ; 
_ (2) Aftershaft present ; 
(3) Distal barbules of inner vane of remiges with minute dorsal 
prongs on cells bearing ventral teeth (undeveloped in Pelecanoides), 
the ventral teeth bifurcated or jagged, ventral cilia well developed, 
slender and flexible, and the basal dorsal cilia triangular, gradually 
becoming slender ; 
(4) Distals of outer vane of remiges differing in having more 
slender base, hooklet region of pennulum wider, hooklets more nu- 
merous, and basal dorsal cilia absent ; 
(5) Proximals of inner vane of remiges with very long slender 
base, with elongated, delicate, wavy ventral teeth, and with pen- 
nulum stout basally ; 
