Galls on the upper side of the leaves of Urtica gracilis, either on the midrib, or, more often, on the lateral veins. Urn-shaped (I mean the shape produced by cutting off the
smaller end of a slender pear) up to 3 m. m. high, subsessile (that is, connected by a very small surface with the leaf), pale green, semi-transparent, succulent gall, bearing a short style or nipple at the upper, truncate end. Inside, the larva of a Cccidomyia. Lake George, July, 1863 ; Trenton Falls, July, 1874 ; not uncommon, but not in large numbers. Each leaf bears one, sometimes two galls, seldom more.

- Baron Von Osten Sacken: (1875) THREE NEW GALLS OF CECIDOMYIA^©

Reference: https://www.biodiversitylibrary.org/item/22105#page/216/mode/1up