302 University of California Publications in Zoology I Vol. 13 



show an almost perfectly intermediate position between penguins 

 on the one hand and Proeellariiformes on the other. In the struc- 

 ture of the breast feathers and down, loons come much nearer the 

 Sphenisciformes than do grebes, and they are also more similar to 

 the Proeellariiformes. 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 

 Alcidae. 



e) Summary 



Colymbif ormes 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 booklets and ventral cilia, and stout, tri- 

 angular, proximal dorsal cilia; 



(3) Distals of outer vane with elongated base, the booklet region 

 of pennulum broad, and a considerable increase in number of booklets ; 



(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 37 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- 

 bif ormes. In Diomedea it is very minute, while in Pelecanoides it 



