362 Unwersity of California Publications in Zoology  'Vou. 18 
wider light interspaces, as for instance, in the breast of Gowra (pl. 
29, fig. 66b-c). It is very unusual, in parti-colored barbules, for 
any pigment to be present ventral to the row of nuclei. A beau- 
tiful, delicate olive color is produced in the coverts of Osmotreron 
by distal barbules in which the base is bluish gray, due to eross- 
bars of black pigment, while the entire pennulum contains a deep 
lemon-yellow pigment (pl. 29, fig. 69a). The iridescent neck feathers 
of Columba, Zenaidura, and other genera are produced by 
barbules from which the pennula are broken off, the reflecting sur- 
face being the large recurved flange. The barbule drawn on plate 
29, figure 57b, from a neck feather of Columba fasciata is seen in 
side view, and nothing of this portion except the tips of the ventral 
teeth shows as the barbules lie in the vanule, the result being that 
these feathers are not iridescent on the ventral side (see also Strong 
1903). 
e) Relationships 
The Pteroclo-columbae, according to their feather structure, 
show more similarities to the gallinaceous birds than to any other 
group. The shape of both distal and proximal barbules, and the 
specialized nature of the down, are all points of striking likeness. 
The occurrence in the tinamous, which are undoubtedly a special- 
ized group of gallinaceous birds, of both the columbid and galline 
type of down, might be considered a further bond of union between 
the two latter groups. They show the same affiliation to some of 
the gruiform birds as do the gallinaceous birds, and like the latter 
show some affinity to the Cuculiformes, especially in the presence 
of prongs on the hooklets of the distal barbules of back and breast 
feathers. The relation of the Pteroclo-columbae to the Laro-limi- 
colae, if there is any close relationship, is not shown at all in the 
structure of the feathers. The Pterocles show a number of differ- 
ences from the Columbae in feather structure, which are probably 
specializations of their own, and do not show closer approximation 
to any other group. 
f) Summary 
(1) Plumules sparse or absent. 
(2) Aftershaft rudimentary or absent. 
(3) Distal barbules of remiges with short, broad base, nuclei in 
strikingly diagonal line, ventral teeth broad and triangular; pen- 
