96 ON THE CLASSIFICATION OF BIROS. 
the genus Psaris, for instance, there is a very slender, 
lanceolate feather inserted betiveen the first and second 
quills, which seems totally useless for any purpose of 
flight, but which must have some especii reference to 
the habits of these birds. The second quiU of the 
white-headed tody of the old authors* is precisely of the 
same structure as that seen in Psaris, yet here it is not 
sliorter, but longer than the preceding, and therefore 
must be used as much for flight as an ordinary quill. 
The four first quills of the Piprn pareola are nearly of 
the same shape as the preceding, that is, remarkably nar- 
row and pointed, while the fifth and those which follow 
are of the ordinary breath ; these narrow quiUs, moreover, 
have their outer web indented like the blunt teeth of a 
little saw, a circumstance that has never been noticed, 
and which is highly curious. In the genus Oxyrhynchus, 
the outer web of the first quiU is constructed precisely like 
that of* the owl, the lip of each lamina being curved back, 
in the shape of a hook. Sometimes, on the contrary, one 
half or more of some of the quills are of the usual breadth, 
while their terminating end is suddenly contracted 
and obtusely pointed (Jig. 48.): this formation is seen in 
some few species of tlie exotic pigeons belonging to the 
genera Peristera (a) and Ptilonapus (6). It cannot, how- 
ever as some have imagined, be taken as a subgeneric cha- 
racter, because perhaps the next species in the series has it 
not; and it is probably only a sexual distinction. The 
Cassicus coronatus of Mexico shows us another example 
of unequally formed primaries. These are instances of 
unusual narrowness. Among those of an opposite descrip- 
• The situation of tHs curious bird is uncertain. It irtay probably 
enter into the circle of the Fluvicolirue^ or water chats. ^ 
