306 University of California Publications in Zoologij I Vox.. 13 



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 flexules 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, booklet region of pennulum wider, booklets 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; 



