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406 ENTOMOLOGICAL NEWS. [Nov., ’08 
cell is sessile. Fig. 6 is from another specimen of the same 
genus showing this cell broadly sessile. 
Figs. 7, 8 and 9 show the variations that occur in the length 
of the petiole of this cell and also variations in the size and 
shape of the discal cell in Tipula aequalis Doane. 
The position of the posterior cross-vein is a specific character 
that is often used and is quite constant in some species, In 
other closely related species it may be of no value on account 
of the variations that occur. Fig. 10 shows the wing of 
Dicranomyia badia O. S. with the posterior cross-vein in its 
normal, that is, most usual, position, but it is é6ften found much 
anterior to this as shown in Fig. 11. Figs. 12 and 13 show the 
variations that may occur in the position of this vein in the 
right and left wings of the same individual. (Limnobia trio- 
cellata O. S.) 
In certain groups we often find extra or “supernumerary” 
cross-veins that may or may not occur in all the individuals of 
the species or they may be present in only one or in both of the 
wings. Whenever they do occur their position is quite constant 
for the species and sometimes for the genera. Fig. 14 shows 
such a vein occurring in the sub-marginal cell of both wings of 
a specimen of Limnobia triocellata O. S. 
A short stump of a vein often occurs near the origin of the 
praefurca in some species. In Fig. 11 (Dicranomyia badia O. 
S.) and Fig. 15 (D. Stigmata Doane) two such veins are 
shown. 
Fig. 15 also shows a remarkable case of a distinct piece of 
a vein occurring in a part of the wing where a vein never oc- 
curs normally 
All or a part of a vein may sometimes be wanting in species. 
where it normally occurs. Fig. 10 shows two such veins in 
the region of the discal cell. Only rarely do we see interpolated 
cells as shown in Fig. 16 (Limnobia sciophila O. S.) and Fig. 
17 (Tipula simplex Doane). Both of these aberrations occur 
in the right wing only of these two specimens. 
These few examples selected from many that might have 
been used show two things: first, the ever present tendency to 
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