226 NEW YORK STATE MUSEUM 
very puzzling; for such characters as this have been found 
elsewhere in the Diptera most reliable. But it is to be noted 
that in all these cases of departure from the assumed Tipulid 
type of forking of the sector, the branches are all long and 
the forks lie close together, and a slight migration of either of 
the three branches would change the relations of the forks to 
each other. The accompanying diagram illustrates these dif- 
ferences of behavior of the radial sector. There are some 
reasons for believing that these peculiar forms are only apparent 
exceptions to the rule of Tipulidae. For example, the position 
of the r-m cross vein in Pedicia, Amalopis and Rhicnoptila, indi- 
cates that in these forms at least, after the complete fusion of R* 
and Rh®saeiurther fusion On Rane withthe spanierOrmuncn section 
immediately before it, brought about the apparent reversion of 
the fork; for, elsewhere when the sector is three branched, this 
cross vein touches the posterior branch after its separation from 
the middle branch but here it touches before this separation | fig. 
14¢]. In other words, the r-m cross vein remains in its original 
position, while fusion has carried the fork past it. A reason for 
that further fusion may possibly have lain in the arcuation of the 
wing apex in these genera. 
In Gynoplistia [pl. 20, fig. 1] the fusion has proceeded only 
to the level of the cross vein, and the two forks are of equal 
dein, in MoOlOpiMiluUs (aor Brio prera) COmatus 
IDrowwne “PING We) Inia; Sees jobire, VOL S, jl 7%, ime, AO] Une ikowiss 
are symmetrically arranged about the middle branch [like f in 
fig. 14]. Obviously this condition, although intermediate, is not 
primitive, but secondary, and has come about through migra- 
tion of one or the other or both of the forks. 
To the other cases in which this exceptional mode of branch- 
ing of the sector occurs, Conosia [pl. 21, fig. 5] and Molophilus 
[pl. 22, fig. 6] the same reasons for this second fusion will not 
apply: the wing tip is not arcuated, but straight. But in both 
of these the r-m cross vein is located unusually far out from 
the base of the wing, especially in the former, and this second- 
ary fusion may here be an accompaniment of the upward 
skewing of the sector, and the unusual relations borne by the 
elements of the cord [fig. 14h]. 
Professor Comstock pointed out that the two modes of 
branching of the sector are differences of kind, and he showed 
that by further reduction either kind of three branched sector 
