ly of much-branched fibers with a considerable amount of small, open space, giving a suggestion of main fibers radiating from the center as in the galls of the American subgenus Atrusca. The larval cell usually central, oval, averaging 3.5 by 4.0 mm., with a distinct wall but inseparable from the spongy filling of the gall, the spongy material directly outside the larval cell, sometimes irregularly compacted and as hard as the cell wall itself. Attached to the median or lateral veins by only a slight point, on the leaves of numerous species of European white oaks.
BISEXUAL GALL.—A small, egg-shaped, thin-walled cell originating in the adventitious buds of the older or younger oak stems. The cells up to 3.0 mm. in length, their surfaces microscopically puberulent, at first red or violet, finally blackened; the entire gall inside the thin shell occupied by the larval cell. Sessile on the old bark near the base of the trunks, less often on the younger stems, but often on the older bark of large stems, a third to a half enclosed by the normal bud scales. Known from Quercus pedunculata, Q. sessiliflora, and Q. pubescens.
RANGE.—Probably wherever oaks occur in Europe, Asia Minor, and northern Africa, with the four described varieties, atrifolii, folii, flosculi, and ilicicola, confined to more northern, central, and Mediterranean Europe and Spain respectively (fig. 15, 16).
The galls of the typical variety of this species are among the commonest and best-known of Central European Cynipidae. This was one of the five species of oak galls known to Linnaeus (1758), and later workers on cynipid structure and biology, and on gall histology and embryology have usually included this species in their studies.
The variety folii ranges over the whole of Central Europe, being replaced in the Mediterranean area of Europe and Africa by a very similar insect, variety flosculi (better known from its agamic form pubescentis) which has certainly been derived from the same stock as typical folii. The insects of the two are so close that most authors have considered them inseparable, and no one, except Tavares (1928), has described more than color differences which, I believe, are not invariable enough for the separation of even the majority of the specimens. I find the smooth foveal groove, the smoother anterior portion of the scutellum, and the enlarged tip of the second abscissa of the radius of flosculi will serve for the recognition of the insects I have seen. The agamic galls of folii and flosculi are quite distinct (except in certain transition areas), and this seems to have been the basis on which determinations
