NORTH AMERICAN ODONATA. 163 



yet been established, the uoniench\ture here used will be thai of de 

 Selys and Hagen. 



At the base of each wing are five large longitudinal veins, whose 

 names, beginning at the front margin, are costa, mbcosta, median, 

 mhmedian and post-costa. At the basal extremity of the costa is a 

 thickening, the anterior axillary callus, and a simWar posterior axillary 

 callus lies at the base of the median and submedian veins. The 

 structure of the base of the wing and of the adjoining thoracic region 

 has been described and figured by Lendenfeld (4) with a minuteness 

 of detail into which it is not necessary to enter here. 



The costa coincides with the front margin of the wings from base 

 to apex ; at a varying distance from the base it curves in and then 

 out again forming a wide, but distinct angle. At this point a short, 

 thick cross-vein exists — the nodus. Parallel to the costa and next 

 below it is the subcosta, running from the base, but stopping at the 

 nodus, except in a few exotic forms. Below the subcosta and parallel 

 to it is the median vein, the third of those which start from the base 

 of the wing ; upon reaching the nodus, it bends upwards towards 

 the costa, next below which it continues to the apex of the wing. 

 Between the median and submedian veins, at the extreme base of 

 the wing is the basilar space {upper basal cell of Kirby), usually not 

 crossed by veins, and whose apical boundary is a straight or l)rokeu 

 cross-vein, the arculm. From the apical side of the arcuhis, two 

 longitudinal veins arise, the tqyper and lower sectors of the arcuhis. 

 The space between the submedian and post-costal veins is the viedian 

 space {lower basal cell, Kirby), and the area between post-costa and 

 the hind margin of the wing is the jiost-costal space. 



Thus far the description given will apply to all the Odonata. For 

 the further arrangement of the veins, it will be necessary to refer to 

 certain groups separately. If the wing of any North American 

 Odonate, other than a Calopterygine, be examined, it will be seen 

 that the median vein does not give rise to any longitudinal veins, 

 but that four conspicuous longitudinal veins are given off", directly, 

 or indirectly, from the upper sector of the arculus. These four 

 veins are from above downwards — 1. the principal sector, imme- 

 diately below and parallel to the median vein ; 2. the nodal sector, 

 which parts from the principal at or near the nodus; 3. the subnodal 

 .sector, parting from the principal some distance on the basal side of 

 the origin of the nodal ; 4. the median sector (to be carefully distin- 

 guished from the median vein), whose point of separation fmm the 

 principal lies on the basal side of that of the subnodal. 



TEANS. AM. ENT. SOC. XX. JULY, 1&93. 



