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Rh

RANGE.—Denmark: Bromme (Hoffmeyer; types). Strödam in Sjelland (hybrids; Hoffmeyer in Kinsey coll.).

Finland: Lojo (hybrids; Forsius in Kinsey coll.).

France: Buchy (Noury in Kinsey coll.).

Probably in a more northern area, chiefly near the northern limit of oak in Europe.

TYPES.—35 females, no galls. Holotype and paratypes in the Kinsey collection; paratypes at the American Museum of Natural History, the U.S. National Museum, the British Museum, and the Vienna Museum. Labelled Bromme, Denmark; galls September 29, 1927; E. B. Hoffmeyer collector.

Among more than a thousand insects of the whole species divisa which I have from various localities in Denmark (all Hoffmeyer coll.), I find 35 specimens which are strikingly different from the Central European material in their much smaller size, nearly jet black color, more naked abdomens, and distinct wing venation. They indicate an hereditary development that has not been noted heretofore, as far as I can find, in divisa of more Central Europe. In this same material there are 178 specimens which are in one or more respects intermediate between typical divisa and atridivisa but close to atridivisa. I have only six insects of this species from Finland, all of which are similarly intermediates, but the occurrence of this same tendency in the Danish and Finnish material supports the idea that atridivisa is a distinct northern variety. This interpretation is also supported by the parallel occurrence of northern varieties of folii and longiventris. The single specimen of atridivisa and the single hybrid among the more than a hundred insects from northwestern France suggests that the northern form may have been pushed southward, during the Pleistocene glaciation, to hybridize with the southern relative, just as we have explained the hybrid Cynips in the United States (see pp. 55 to 60).

The data on the European insects are summarized in the following table.

The galls of our type series of atridivisa were not isolated from those of the typical divisa, from which they probably do