The C-band, or costal band, extends from the base of the wing along the anterior margin to the apex of vein R₁. The S-band extends obliquely from the base of cell cu₁ across r-m, reaching the anterior wing margin in cell r₁, then following the anterior margin to the wing apex. They are usually separated basally by a hyaline area of varying size, extending from cell bm, sometimes all the way to the anterior wing margin in cell r₁.