1916] Chandler: Structure of Feathers , 315 



19, figure 19e. Unfortunately these two figures were reversed in 

 position from the system usually followed in the preparation of 

 the plates. 



c) Down 



The down of Steganopodes, like the pennaceous structure, is 

 extremely variable. In Phalacocorax, Fregata, Pelecanus and Phae- 

 than the downy barbules are of moderate length, i. e., from 1.0 to 

 1.3 mm., and smoothly filamentous except in Pelecanus, which has 

 minute prongs at the nodes on the distal portion of the barbules. 

 In Plotus the downy barbules (pi. 34, fig. 99) are also filamentous, 

 but are very long, frequently reaching a length of over 2 mm. Sula 

 differs not only from other Steganopodes but also from all other 

 birds in the enormous development of the prongs at the nodes. These 

 reach a length of over 0.1 mm. in barbules which are only 0.6 to 0.8 

 mm. long, being slender, filamentous, and frequently bifurcated 

 (pi. 34, fig. 98). The only other birds which begin to approach Sula 

 in the length of the prongs are albatrosses and puffins, and this might 

 be looked upon as additional evidence of fairly close relationship 

 between the Sulidae and the Procellariiformes. 



d) Relationships 



The Steganopodes are a group of birds in which primitive char- 

 acters are curiously combined with specialized characters, the result 

 being a rather heterogeneous aggregation of more or less related 

 forms which are specialized along different lines. They seem to 

 fall into three fairly well-defined groups as follows : ( 1 ) Phalaco- 

 corax, Fregata, Sula and Pelecanus; (2) Plotus; and (3) Pha'e- 

 thon. 



The first group may be regarded as containing the most tj^pical 

 Steganopodes, since they form the bulk of the group, and are 

 least specialized. They seem undoubtedly to be derived from a 

 primitive procellariiform type, and as certainly to stand at the 

 base of the ciconiiform group, the next above them being the 

 Ciconiae. 



The second group, including only the neotropical genus Plotus, 

 though often grouped only as a sub-family of the Phalacocoracidae, 

 differs very widely from the other Steganopodes in the structure 

 of its feathers, in which it is very specialized. In some details of 

 the feather morphology this genus shows such striking similarity 



