Figure 2 in A unique, large-sized stem Odonata (Insecta) found in the early Pennsylvanian of New Brunswick (Canada)

Figure 2. Characterization of vein fusion: (a) two veins are connected by a cross-vein, the points A and B overlap, and C and D overlap, distance a is superior to distance b; (b) two veins are briefly connected, the points A and B overlap, and C and D overlap, distance a is slightly superior to distance b; (c) two veins are connected, the points A, B, C and D overlap, distance a equates distance b; (d) two veins are fused, the points A and C overlap, and B and D overlap, distance a is inferior to distance b.