Tr. ent. Soc. London, 1884, p. 149.
Ann. Soc. ent. France (5), iv. 1874, p. 567.
See Pérez, Act. Soc. Bordeaux, xxxiii. 1880, p. lxv.; and Cameron, Tr. Soc. Glasgow, n. s. ii. 1889, p. 194.
Ann. Nat. Hist. (6), xix. 1897, p. 136.
Janet has suggested that the folding is done to keep the delicate hind-margins of the wings from being frayed.