316 University of California Publications in Zoology Vor. 138 
to the Cathartae that their kinship can hardly be doubted. This 
will be forcibly shown by a comparison of plate 18, figures 13a and 
13b, 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- 
earding the Cathartae as direct descendants of the Steganopodes, 
from a form not far removed from Plotus. 
The third group, Phaéthontidae, 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 ae, 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 
Phaéthon. 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, hooklets 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; hooklets short; proximal barbules with 
tendency to develop weak ventral cilia; 
