The principal entrance, reached by a flight of 23 steps, is ornamented with a portico supported by four black-veined marble columns.
Membranous, net-veined wings, those of the two pairs closely alike.
Wings usually well developed, net-veined; the forewings of firmer texture than the hind-wings, whose anal area folds.
A remarkable fossil from the Scottish Coal-measures (Lithomantis) had apparently small wing-like structures on the prothorax, and in allied genera small veined outgrowths - like tracheal gills - occurred on the abdominal segments.
For the architectural embellishment of the city the finest building material was procurable without difficulty and in abundance; Pentelicus forms a mass of white, transparent, blue-veined marble; another variety, somewhat similar in appearance, but generally of a bluer hue, was obtained from Hymettus.