On leaf, under side, greatly depressed with central, prominent nipple,
3-5 mm. dia. 1½-2½ mm. thick (vertical dia.) not including nipple.
Light green, smooth. Firm fleshy with central sub-spherical larval
chamber whose wall is differentiated from the surrounding tissue.
Apical canal through nipple evident. This gall first reported and
illustrated by Thompson.
Thompson, Illus. Cat. Am. Ins. Galls. 1915. p. 56, pl. 13, Fig. 228.
A most interesting variant of this form is illustrated in Fig. 16a.
If it were not for the large number of intermediate forms found, this
one would easily be considered distinct. The region of the chamber
surrounded by thick walls has been much reduced, so that only a
circular area about the upper part of the chamber has the thick wall
projecting from it. This new condition results in the formation of a
definite saucer-shaped structure on the distal end of the gall. In
some specimens the structure was no longer saucer-shape, but by the
ingrowth of the edges it was assuming a spherical form, developing
a two-chambered gall. It is natural to suspect that this may have
been the mode of origin of the four-double-chambered galls described
elsewhere in this paper. That, however, is entirely problematic.