316 University of California Pivblications in Zoology [Vol. 13 



to the Cathartae that their kinship can hardly be doubted. This 

 will be forcibly shown by a comparison of plate 18, figures 13a and 

 13&^ with plate 22, figures 34 a and c. This close similarity of the 

 Cathartae with Plotus, accompanied as it is by other common char- 

 acters as shown by Gadow (1891), suggests the possibility of re- 

 garding the Cathartae as direct descendants of the Steganopodes, 

 from a form not far removed from Plotus. 



The third group, Phaethontidae, is so strikingly like the Laridae 

 that their affiliation with the Steganopodes seems very doubtful, 

 and if feather morphology be considered, they should be looked 

 upon rather as aberrant larid forms. Comparison of plate 19, 

 figures 19 a-f, with plate 28, figures 61 a-e, will make clear the 

 marked similarity in feather morphology. 



e) Summary 



The Steganopodes are divisible into three groups on the basis 

 of feather morphology, the typical Steganopodes, Plotus, and 

 Phaethon. The first group is characterized as follows: 



(1) Plumules uniformly distributed; 



(2) Aftershaft absent or rudimentary; 



(3) Distal barbules of remiges relatively small as compared 

 with proximals, and much more numerous, the difference in num- 

 bers much greater than usual; 



(4) Distal barbules of remiges with short, broad base, with 

 broad lobate ventral teeth, except in Sula, where they are relatively 

 small and narrow; pennulum moderate in length, booklets slender 

 and progressively longer, ventral cilia long and slender, basal dorsal 

 cilia, on inner vane, stout and triangular, gradually changing to a 

 spiny, and ultimately a filamentous form; - 



(5) Proximal barbules of remiges with base long and large rela- 

 tive to distals; ventral teeth long and conspicuous on inner vane, 

 transformed into a weak series of ventral cilia on outer vane; 

 pennulum rather broad, usually shorter than base, but sometimes 

 as long. 



(6) Back feathers with bases of both distal and proximal barbules 

 elongate, the distals with long pennula, with double series of well- 

 developed slender cilia, except where specially modified for produc- 

 tion of iridescent color ; booklets short ; proximal barbules with 

 tendency to develop weak ventral cilia ; 



