314 University of California Publications in Zoologjj 1 Vol. 13 



should be compared with plate 17, figures 12a and 12&. Pelecanus 

 calif ornicus has the same type of structure. 



(5) Phaetliontidae 



The Phaethontidae or tropic birds, as far as feather structure 

 is concerned, seem to show a perfect transition from the Procel- 

 lariiformes on the one hand to the Laro-limicolae on the other, 

 though apparently more closely related to the latter. As shown by 

 plate 19, figure 19a {Phaethon ruhricauda), the base of the distal 

 barbules of the inner vane is relatively large and broad, and the 

 ventral teeth long and slender, with a very slight tendency to 

 bifurcate, not always displayed, however. The booklets are only 

 four in number, and relatively short and small, the ventral cilia 

 are much reduced, and the dorsal ones likewise, except the basal 

 two, which are strongly reminiscent of Laro-limicolae. The prox- 

 imal barbules (pi. 19, fig. 19&) differ from those of other Stegano- 

 podes, but agree with the Laro-limicolae in their relatively small 

 size, and in having small inconspicuous ventral teeth. There is 

 another significant difference in the relative number of distal and 

 proximal barbules. In all other Steganopodes there are nearly 

 twice as many distals as proximals, while in Phaethon there are 

 22 or 23 proximals to 30 distals, this genus thus resembling both 

 the Procellariiformes and the Laro-limicolae, The barbules of the 

 outer vane, the forms of which are shown in plate 19, figures 19c 

 and 19d, are characterized primarily by their slender form, the 

 wide separation of the booklets of the distal barbules, which are 

 all of nearly equal length, and the weak ventral cilia of the prox- 

 imal barbules. The rami of the outer vane have the ventral edge 

 serrate and broken into villi, a condition which reaches the height 

 of its development in the Anseres. 



The barbules in back feathers of Phaethon ruhricauda closely 

 resemble those of the inner vane of the remiges, except in their 

 smaller size. 



The breast feathers, as in Pelecanus among Steganopodes, and 

 like the Procellariiformes and Laro-limicolae, develop flexules, but 

 not as numerous or as well-formed ones as in Pelecanus. Plate 

 19, figure 19e, shows a proximal barbule from the terminal por- 

 tion of a barb from a breast feather, while figure 19/ of the same 

 plate shows a distal barbule from a portion not quite so near the 

 tip. Its base is much reduced, and it has weak barbicels; a little 

 more distally it assumes a form similar to that represented in plate 



