1S63.] 
209 
Sectors (branches springing from areas, veins, cross-veins, or other 
sectors).— -fff. principal sector, g, nodal sector, /i, subnodal sector. 
median sector, mm^ short sector. upper sector of the Triangle, 
(normally a prolongation of cZ.) o, lower sector of the Triangle, (nor¬ 
mally a prolongation of c.) o', o" its branches, (g-amecmx 
Cross-veins.— p. nodus, g, arc or arculus. rrr---- antecubitals.f 
^ss -postcubitals. 
Areas and angles.—the Triangle, (discoidal.) internal 
triangle. F, anal triangle. IF, basal area (or space.) xx^ median area 
(or space.) //, membranule. anal angle in S , the dotted line z' 
shewing the form of the anal corner of the wing in 9 Gomphus.\ AA----, 
discoidal areolets, (in the figure, two ranges of them commencing with 
three.) i?, Pterostigma. (7, its basal (or internal) side prolonged in 
the normal manner, i), “ quadrangle,” quadrilateral,” or area 
above the triangle,” bounded above by m, below' by r/, basally by q. 
and terminally by an unnamed cross-vein. EEE, Postcostal area 
(or space.) 
Of the above pterological parts, q and its sectors, r, .b-, IF, y, 7i, 
and in Calopterygina and Agrionina “ the quadrilateral” (D) and “ the 
postcostal area” (E) are the most important in Classification. When 
in Odonata antecubitals” and ‘‘ postcubitals” are spoken of, the an¬ 
terior or costal series of each, in the front wing, is always meant, unless 
express reference is made to the antecubitals and postcubitals of the 
hind wdng, or to their posterior or subcostal series. The triangles are 
said to be ^‘free” {Jlhres) or “empty” (vides), when, as in Gomphus^ they 
are not intersected by cross-veins. In Gomphoides^ Gordidegaster^ and 
most other triangle-bearing Odonatous genera they are so intersected. 
The discoidal Triangle (^) is usually called simply “the Triangle.” In all 
my Gomphiis (60 or 70 specimens of different species, including J/or- 
rogomphns spluicep^ Walsh) the first and fifth antecubitals are more 
robust than the others both in the costal and subcostal series, and are 
The figure gives an angle where o' bifurcates from 0 , which should have 
been a flowing curve. Both n and 0 should have been engraved as springing 
from the lower angle of the triangle (i^). 
f The basal antecubital is wrongly engraved as dislocated with that of the 
2nd or subcostal series. 
j The angle z ought to have been engraved as miudi more acute and salient. 
