44 



THE SCOLYTID BEETLES. 



Basal area (fig. 30). — The basal area is that m which the basal 

 plates and head of the veins occur. In this area there are four 

 axillary plates, which are more or less common to insect wings in 

 general. These appear to belong to the wing rather than to the 

 body structures, and are here designated as scapular, subscapular, 

 flexor, radial, and medial plates. They are discussed in greater 

 detail under wing articulation. 



Veins. — The six primary veins represented in the hind wing are 

 costa, subcosta, radius 1 and 2, media 1 and 2, cubitus 1 and 2, and 

 anal, which last is rudimentary. 



\)„sal «'■''« 



Fig. 30.— Dendroctonus valens: Diagram of basal area of hind wing, o, Scapular plate; 6, subscapular 

 plate; c, flexor plate; d, radial plate; e, medial plate; /, tendon attachment; 9, articulation; 7i, subcostal 

 head; i, costal head; j, costal tongue; k, radial head: I, medial head; m., cubital head; n, anal head; 

 0, scapular condyle; p, scapular arm; q, scapular base; r, articulatory margin; s, connection of costa 

 with subcosta; «, flexor arm; «, connection ofmedial plate with flexor; C, costa; Sc, subcosta; iJ, radius; 

 if, media; Cm, ^ 5, cubitus 1 and 2; ^, anal. (Original.) 



Costa. — In DeTidrodonus and most beetles the vein which corre- 

 sponds to the costal trachea is confined to the basal area, and forms 

 the anterior basal angle. The head is produced beyond the head of 

 the subcosta, with which it is fused to form the articulating fossa. 

 The produced head of this vein appears to function as an important 

 accessory of the clavicle muscles in extending and depressing the 

 wing, smce it is connected with the clavicle condyle and clavicle disk 

 by tendons. The vein proper extends outward but a short distance 

 to its submembranous connection with the subcosta, and from that 

 point the costal margin is occupied by it and the subcosta to its 



