The genus Corethra was founded by Meigen in 1803,* on Tipula culiciformis, De Geer, and in April, 1844, Leow erected the genus Mochlonyx† on Corethra velutina, Ruthe, basing it on the shortened first joint of the tarsi, a character mentioned by Ruthe in his original description. The characters of the tarsi of culiciformis cannot be ascertained from De Geer's description and figures.‡ On page 386 of the same volume of his Memories, which contains the account of this species, is a description and brief account of a related species, which he named Tipula crystallina, with a reference to Reaumur's Memories, V., plate 6, figures 4–15, where at 4 and 7, a more slender larva without a trace of a subanal respiratory tube in shown, contrasting with the broader larva furnished with a large respiratory tube, as represented in De Geer's figures of culiciformis,; the descriptions and figures which these authors give crystallina do not indicate the characters of the tarsal joints of the adult.