Formed in summer on the underside of the leaves of Quercus obtusiloba, Q. macrocarpa, and Q. alba, often to the number of 1,000 on a single leaf: each gall inserted in a deep cavity which causes, on the upper surface, a bulging of a straw-yellow color, irregularly sub-conical, with the top flat-tened or concave, and with a minute central nipple, sometimes obsolete; the galls becoming detached and falling to the ground in autumn, leaving a pale, fulvous, circular disc at the bottom of the; cavity. The gall has an average diameter of 1 mm., and the color and general appearance of a miniature acorn - the base being paler than the sides and conically produced to the central point of attachment. The apical portion is slightly constricted into a deep purple-brown rim, and the top within this rim is flat, with a small central nipple.

Received at different times from M. W. Harrington, of Ann Arbor, Mich.; from Irvin Armstrong, of Vevay, Ind.; from N. B. Baldwin, of Elgin, Ills., and from Win. R. Howard, of Forsyth, Mo.; also sufficiently common in St. Louis county.