Kinsey: The Genus Neuroterus 
17 
beir.g found in each place. The biologic separation of Europe 
and America has been long enough to allow distinct evolutions. 
But this isolation could not have occurred before the origin 
of two, primitive, ancestral types which were the sources 
of all (but one?) of the subgenera. The European subgenus 
Neuroterus is more closely related to the American subgen- 
era Diplobius and Dolichostrophus than to the other European 
groups; and the European Spathegaster is closely related to 
the American Neo spathegaster. The European Pseudoneu- 
roterus is more distinct, but shows relationship to Spatheg- 
aster. Each of the three subgenera which are confined to 
the Old World contains only one or a very few species. The 
number of monospecific groups in that region is very striking ; 
the explanation should be sought in the geography and geol- 
ogy and, in the case of Cynipidse, in the oak host distributions. 
It is proper that European workers have shown some hesi- 
tancy in establishing separate genera (or subgenera), for 
single species, but a comparative study of the Neuroterus 
species of the whole world warrants it. 
One of the American subgenera is monospecific, but each 
of the others has several species. Some of these may be 
due to some former separation of eastern and western North 
America, and to the present-day isolation of our Pacific 
Coast; but the number of species occurring in the relatively 
uniform eastern United States, with as many as six to nine 
species sometimes on a single host (Q. alba, Q. stellata, Q. 
breviloba) , makes it difficult to explain the larger number 
of the American species as due to either the variety of geo- 
graphic areas or host species. 
The distribution of the American species is as follows: 
4 occur from the Atlantic to the Pacific. 
7 are restricted to Eastern North America. 
3 are restricted to Western North America. 
2 are restricted to the Southwest (Mexican). 
Probably the principal change to come with additional know- 
ledge will be the extension of the ranges of some of the 
species now know only from the eastern United States. Two 
of the transcontinental species occur in Diplobius, and two 
occur, in Dolichostrophus. It is moreover certain that some 
species are not transcontinental, for two pairs of species. 
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