142 FOSSIL INSECTS OF THE BRITISH COAL MEASURES. 



irregularly. The more median part of the costal margin appears as a flat, straight, 

 knife-like edge, crossed by a series of fine striations. 



The thickened pre-costal portion of the outer margin forms a rigid bar, 

 enormously strengthening the wing for flight. The costa is distinct, and passes 

 directly to the wing-apex, as a broad, strap-shaped vein, broadest at its point of 

 origin, and slowly diminishing in width to the tip of the wing. 



The subcosta has an apparent union at its base with the costa, but this is due 

 to a slight backward displacement of the latter. Some distance beyond the 

 thickened margin, the costa bears, at regular intervals, a series of low spines, 

 projecting freely forwards, and gradually inclining towards the wing-apex. A 

 few scattered tubercles, and a faint ridge, are seen along the middle of the vein, 

 and eventually die out. The distal part of the costa is straight, and is joined to 

 the subcosta by a series of transverse branches which are well marked. Of these 

 branches, eleven are still whole, and portions of nine others can be made out. It 

 would therefore seem that the whole of the costal area was covered by a parallel 

 system of straight cross-branches with no intervening network. 



The subcosta arises in close contact with the costa, diverging rapidly until the 

 two are about 5 — 6 mm. apart. Once this distance has been attained, they remain 

 nearly parallel for some distance. There are indications that the two come 

 together some distance beyond the broken edge of the wing-fragment. 



The costa and subcosta are nowhere more than 5 — 6 mm. apart, in the main 

 but 4 mm., the interval narrowing to the broken edge of the wing. While the 

 subcosta has the same flat, strap-shaped character as the costa, it is more delicate, 

 and a narrower vein. A few tubercles are disposed along the median line of its 

 length. 



The radius and median veins being lost, except for the trivial pieces already 

 noted, they cannot be compared with those of Meganeura. In the French species 

 of this genus a complex of parallel veins arises from one or two roots between the 

 subcosta and the cubitus. In the case of M. monyi, this complex arises from a 

 strong radius and a weak median. In M. selysii it would appear that the radius 

 and median are united at their base. In the restoration of the Radstock wing it 

 will be seen that the vein-fragments appear as parts of the median vein, the radius 

 being wholly lost. 



The cubitus is separated from the outer part of the wing by the interval 

 formerly occupied by the radius and median. This interval is variable in width, 

 owing to the strong curvature of the cubitus. This is a large flattened vein, 

 strongly flexuous, and finally curving inwards to reach the middle of the inner 

 margin. The base of the vein has been broken away and lost, but its course may 

 be indicated by a faint groove which curves forward towards the base of the 

 subcosta. The outer inward curve of the cubitus is the greater, so that the 

 interval between the radius and the subcosta becomes increasingly wide, thus 



