This, the typical subgenus of Cynips, seems confined to Europe and the adjacent Mediterranean shores of Asia Minor and Africa. There it is the only subgenus of Cynips represented. Further collecting may show that the group extends eastward across the whole of Asia; but it is evident enough that the five American subgenera, altho they have had a common origin with European Cynips, are as distinct as their not inconsiderable period of geographic isolation would lead us to anticipate. The closest American relatives of the European Cynips are the Pacific Coast subgenera Antron and Besbicus.
European Cynips is known from eleven varieties which represent the geographic segregates of six species. The most unique of these, Cynips cornifex, is confined to a limited part of the Mediterranean area in Europe. The other five species probably range as far as oaks extend in Europe, and at least some of them occur in northern Africa and Asia Minor. Each of these five species was first described from central European material; but each of them may also have a distinct northern variety (only three of which are described to date) and one or more Mediterranean varieties (only one of which is described!).
Studies of the geographic distribution, the host isolation, and the phylogenetic origins of the European fauna cannot progress very far when they are based on as uniform an area as that which constitutes Central Europe, or on a single species of host, which is essentially the oak flora (Q. Robur and its minor variants: Q. peduncidata, Q. sessiliflora, Q. pubescens, etc.) in Central Europe. In America we have found the comparative study of groups of related varieties an unsurpassed means of interpreting biologic phenomena. The Central European fauna may offer similar possibilities if it is compared with its adjacent faunas.
It should be emphasized that the study of cynipid varieties must be based on insects as well as on galls. We have many cases among our American Cynipidae where the varietal characters are not evident from the galls alone, and the herbarium collections in vogue among European “Cecidologists” will contribute little toward phylogenetic studies until they are fortified by large series of insects representing (for the Mediterranean region) each of the species of oaks or groups of closely related oaks involved.
