TO DUS. 
161 
named, is pre-eminently typical ; and we shall find, 
upon close analysis, tliat the variation of its species, 
as in the sub-genus Bos*, turns out to he regulated 
by the very same law ; they actually become types 
of form. And we shall find these types almost as 
distinctly marked as if they belonged to a family, 
instead of merely representing the succession of 
species in a sub-genus. 
The most universal character of the typical todies 
is their flat elongated bill, in opposition to that of 
Plalyrhynchus , which, although equally flattened, 
is remarkably short ; the sides are bristled, but 
these bristles are short and weak, and in some species 
are almost obsolete. The wings and tail are short, 
but the latter is much more conspicuous than in 
Platyrhynchus, while the form of its termination 
indicates the variation of the species and the posi- 
tion they occupy in the series. Tlius, in the Todus 
viridis the tail is even, in melanocepkalus t it is gra- 
duated, in meyacephalus X it is shortest, and the end 
is rounded ; while in platycircus it is longest, with 
the feathers broad, but terminating in points. The 
other species yet discovered fill up the' intervals, and 
arrange themselves close to one or other of those 
just named. The variation in the length and struc- 
ture of the feet is no less remarkable. These 
members are always sufficiently long to point out 
the sub-genus ; their variation is consequently com- 
* Classif. of Quadrupeds, p. 281. 
+ Spix Av. Nov. ii. pi. 9, f. 2. 
t Omitli. Drawings, pi. 
L 
