1916] Chandler: Structure of Feathers 317 



(7) Breast feathers similar but weaker, without flexules except on 

 outer part of barbs in Pelecanus and Sula; 



(8) Down barbules of moderate length, smoothly filamentous, 

 or with minute prongs at nodes on their distal portion except in Sula, 

 where prongs at nodes are enormously developed, to an extent 

 approached among other birds only in some Procellariiformes. 



Plotus, constituting the second group, is characterized as fol- 

 lows : 



(1) Proximal barbules very small relative to distals, the length 

 of their bases actually less. 



(2) Distal barbules of inner vane of remiges with ventral teeth 

 lobate, their ventral edge in a continuous line with ventral edge of 

 base; booklets relatively small and very stout, progressively longer; 

 ventral cilia coarse, blunt, and rodlike, more or less appressed to 

 pennulum; no dorsal cilia except one, or sometimes two, stout, 

 blunt, spinelike basal ones, followed by a dip in the dorsal contour 

 of the barbule, thus giving it a characteristic shape. 



(3) Proximals of both vanes of remiges with very short, small 

 base, inconspicuous ventral teeth, and short, conspicuously wide 

 pennulum, with recurved spines. 



(4) Silvery gray color of parts of outer vane due to a greatly 

 expanded and inflated unpigmented pennulum bearing small, stout 

 booklets and extremely long, slender, closely associated ventral cilia. 



(5) Body feathers with distals and proximals both similar to 

 remex type, of which they are mere simplifications; no flexules 

 developed. 



(6) Down barbules smooth and filamentous, and longer than 

 in any other Steganopodes, frequently over 2 mm. 



The third group, including only the monogeneric Phaethontidae, 

 is characterized as follows: 



(1) Distal barbules of remiges large as compared with proxi- 

 mals, and the latter over two-thirds as numerous. 



(2) Twist between base and pennulum of distals producing 

 sharp curve in the dorsal contour as barbule lies in normal posi- 

 tion; ventral teeth small and slender; booklets slender, rather weak, 

 and well separated from each other ; ventral cilia reduced ; and basal 

 dorsal cilia of inner vane lobate, almost exactly as in gulls. 



(3) Proximal barbules of remiges with narrow base, short pen- 

 nulum and short inconspicuous ventral teeth on inner vane, a series 

 of weak ventral cilia on outer vane. 



