Pachypsylla venusta

Generally globular, but often more or less irregularly ovoid, or even elongate. Color varying from pale buff to brown; surface opaque, with scattered, small, flattened postules. Diameter of globular form varying from 7 to 20mm, The gall consists of an outer shell and an inner core, which can easily be separated upon cutting the gall open. The outer shell is very hard and woody, varying in thickness from 1 to 3 mm. The apical portion of the gall has on one side a slit which is deepest and widest at the tip and connects here with the funnel-like, twisted, basal portion of the leaf. This slit exposes to view the inner core, which consists of the very thin and brittle walls of the irregular cells which fill the entire cavity of the outer shell. The number of these cells varies according to the size of the gall, but is rarely reduced to a single one.

The full-grown pupa always leaves the gall through the apical opening, and in doing so has to saw its way out through the top of the inner core.

The gall usually occupies the entire petiole, but in rare instances a small portion of the latter is visible between the gall and the twig.

- CV Riley: (1890) Insects injurious to the hackberry^©

Reference: https://www.biodiversitylibrary.org/item/42358#page/631/mode/1up