302 University of California Publications in Zoology  [Vor. 138 
show an almost perfectly intermediate position between penguins 
on the one hand and Procellariiformes on the other. In the struc- 
ture of the breast feathers and down, loons come much nearer the 
Spheniseiformes than do grebes, and they are also more similar to 
the Procellariiformes. The grebes appear to represent a separate 
offshoot of the group, and have a condition of the breast feathers 
which is different from that of any other birds except some of the 
Alecidae. 
e) Summary 
Colymbiformes are characterized as follows: 
(1) Aftershaft present, its shaft short, and barbs spreading ; 
(2) Distal barbules of inner vane of remiges with small, slender, 
ventral teeth, moderate hooklets and ventral cilia, and stout, tri- 
angular, proximal dorsal cilia; 
(3) Distals of outer vane with elongated base, the hooklet region 
of pennulum broad, and a considerable increase in number of hooklets ; 
(4) Proximal barbules with rather well-developed, slender ven- 
tral teeth on inner vane and a series of hooked barbicels on outer; 
(5) Breast feathers characterized by peculiar twisted barbules 
in Colymbidae, but very reminiscent of Sphenisciformes in Gaviidae ; 
(6) One or two flexules appearing on terminal barbules in 
breast feathers ; 
(7) Down barbules short, strikingly similar to those of the 
Sphenisciformes. 
3. Order PROCELLARIIFORMES 
Plate 17 
The albatrosses, petrels, puffins, and other birds that comprise 
this order form a very well-marked and easily recognizable group, 
and it is not surprising to find that they possess a number of con- 
stant epiphyologic characters. The plumules are evenly distributed 
over the whole body, between the contour feathers and in the 
apteria. The wing is very long in some species, due to the large 
number of secondaries, these varying from 10 to 387 in different 
species. The aftershaft is present, though sometimes very weak 
and vestigial. When well-developed, e. g., in Oceanodroma, its 
shaft is short and the barbs spread out in a tuft as in the Colym- 
biformes. In Diomedea it is very minute, while in Pelecanoides it 
