proliferation of the pith-tissue and scarcely any differentiation of the lining of the larval cells. These cells average 2.0 mm. by 1.2 mm. Externally, the stem shows no trace of a gall.
Range.—Canada: Quebec (Couper Coll.).
Cotypes.—Thirty-three females, twenty males, and ten pieces of infested stems as cotypes, in the collections of The American Museum of Natural History, the Museum of Comparative Zoology, and in the author's collection. The stems were collected about forty years ago. I cut the cotype adults from the stems and many of the specimens are imperfect or barely mature.I cut one parasite, an eurytomid, from the same stems.
The insects superficially resemble the adults of Aulacidea bicolor, but the two species differ in many respects. The most conspicuous key characters of abdita are the rufous face (in bicolor only the mouth-parts are rufous or black), the very prominent median frontal elevation (practically absent in bicolor), the uniformly yellowish red antennæ of the male (the two basal joints are darker or piceous in bicolor), and the large areolet of the male (in bicolor the areolet is small or almost lacking). I have bred large series of true bicolor and have examined material from many localities and there seems to be no variation of the species toward the characters of abdita.
A considerable amount of data which I am bringing together elsewhere shows that the Aulacini are in very many respects the most primitive of the gall-wasps. The biology of species of the genus Autacidea is hardly different from that of “normal” phytophagous Hymenoptera, lacking the remarkable phenomena such as production of complicated gall structures, agamic reproduction, and alternation of generations so characteristic of the higher Cynipidæ. The galls in this genus are all very simple. In this respect the most primitive of all the species we have known previously is Aulacidea bicolor: it produces no gall, but lives in the pith of stems. A very few other species of closely related genera match bicolor in this respect, e. g., Phanacis centaureæ, Aylax rufus, and A. gillettei. But we have not sufficiently realized that there might be many species of Aulacidea with as primitive characteristics, and I imagine that we have carelessly labelled all specimens of Aulacidea which have not come from distinct galls as being of the species bicolor. The difficulty of locating the insects in a plant which shows no external evidence of its infestation also accounts for the previous neglect to discover these primitive species. By extensive collecting of old stems of Lactuca in May and early June, I was able to secure quantities of infested material, breeding large series of insects from it, and I have been surprised at the variety of species obtained. I found true A. bicolor, A. podagræ very abundantly
