116 
GENERAL OMNITHOLOGY. 
have received particular names. A rectrix broad to the very tip, and there cut squarely off, is 
said to be truncate ; one such cut obliquely off is incised, especially when, as often happens, the 
outline of the cut-off is concave. A linear rectrix is very narrow, with parallel sides; a lanceo- 
late one is broader at the base, thence tapering regularly and gradually to the tip. A notably 
pointed rectrix is said to be acute ; when the pointing is produced by abrupt centraction near the 
tip, as in most woodpeckers, the feather is acuminate. A very long and slender, more or less 
linear feather is called filamentous, as the lateral pair of a barn swallow or most sea swallows. 
The vanes sometimes enlarge abruptly at the end, forming a spoon-shaped or sjMtulate feather; 
or such a spoon may 
result from narrowing 
of the vanes near the 
end, or their entire ab- 
sence, as in the ''rack- 
et " of a saw-bill (Mo- 
motus). The vanes are 
sometimes wavy as if 
crimped ; our Plotus is 
a fine example of this. 
Sometimes the vanes 
are entirely loosened, 
the barbs being remote 
from each other, as in 
the exotic genus Stipi- 
tiiriis, and some parts 
of the wonderful caudal 
appendage of the male 
lyre-bird {Menura su- 
perha). When the rha- 
chis projects beyond the 
vanes, the feather is 
spinose, or better, mu- 
cronate (Lat. miicro, a 
pricker), as excellently 
shown in the chimney- 
swift, ChcBtura (fig. 
297)- A pair of feathers 
Fig. 32. — The Lyre-bird of Australia, Menura superba, to sliow the unique abruptly extending far 
Z?/mie shape of the tail. (From Amer. Nat.) beyond the others are 
called long-exserted, after the analogous use of the term in botany. Tail-feathers also differ 
much in their consistency, from the softest and weakest, not well distinguished from coverts, 
to such stiff and rugged props as the M^oodpeckers possess. They are downy and very rudi- 
mentary in a few birds, notably all the grebes, Podidpedidee, which are commonly said to 
have no tail. The tinamous of South America {Bromceognathce) are also very closely 
docked. The 
Typical Number of Rectrices is twelve. This holds in the great majority of birds. It 
is so uniform throughout the great group Oscines, that the rare exceptions seem perfectly 
anomalous. In the other group of Passeres (Clamatores) it is usually twelve, sometimes ten. 
Ten is the rule among Picarice, though many have twelve, a very few only eight, as in the 
genus Crotophaga. The whole of the woodpeckers (Pieidce) have apparently ten ; but really 
