300 University of California Publications in Zoology [Vol. 13 



with single, slender ventral tooth, the latter with 3 or 4 short hook- 

 lets, and a series of curved ventral barbicels. Type same as that 

 in Aechmophorus occidentalis (pi. 16, fig. 9e). Proximals with 

 slender, elongate base, and slender pennulum, the latter with a 

 series of moderate ventral barbicels. See plate 16, figure 9/ (Aech- 

 mophorus occidentalis). On distal portion of feather, both distal 

 and proximal barbules reduced to single elongate type, resembling 

 somewhat proximal barbules of penguins ; no sharp demarcation be- 

 tween base and pennulum, but latter with a series of curved ventral 

 barbicels ; base, on some of terminal barbules, with one or two flex- 

 ules developed (pi. 16, fig, 9g, of Aechmophorus occidentalis), a 

 highly significant fact considering their universal occurrence in 

 Procellariiformes. 



Breast feathers well-developed, with fairly strong vanes. Bar- 

 bules remarkably similar to those of pengiiins ; distals (pi. 16, 

 fig. 8e) with narrow base and weak ventral teeth, pennulum with 

 long series of short booklets, gradually changing to curved ventral 

 cilia, exactly as in penguins ; proximal barbules towards tip of 

 barbs (pi. 16, fig. 8/) with slender tapering base and barbicelled 

 pennulum, the ventral cilia longer than dorsal, but both series 

 present. 



l>) Other Types 



Gaviidae. — Gavia pacifica has practically identically the same 

 structure as the species above described. 



Colymhidae. — In Aechmophorus occidentalis the structure of 

 the remiges is strikingly similar to that of Gavia, differing only in 

 a few details. The rami are not so deep and have not so wide a 

 ventral ridge as in the Gaviidae, and they are set closer on the 

 shaft, there being about 25 and 28 per millimeter on the inner and 

 outer vanes respectively. The barbules are essentially the same in 

 structure as in Gavia, but, as would be expected on smaller feath- 

 ers, they also are smaller; the distals (pi. 16, figs. 9a, 9c), for ex- 

 ample, are only about 0.47 mm. long, the base constituting about 

 half of this. On the proximal barbules of the inner vane (pi. 16, 

 fig. 9&) the base is relatively longer and narrower, with less con- 

 spicuous ventral teeth, while in the proximals of the outer vane 

 (pi. 16, fig. 9d) the barbicels are much smaller and weaker. Colymhus 

 holhoelli and Podilymhus podiceps are similar, but the barbicels of 

 the proximal barbules of the outer vane are still less conspicuously 

 developed, and confined to barbules on a less extensive portion of 

 the barb. 



The back feathers of Aechmophorus occidentalis closely resemble 

 those of the loons. In most other grebes, however, e. g. the various 

 species of Colymhus and Podilymhus, a hairlike effect is produced in 



