246 AMERICAN HYMENOPTERA. 



part of the thorax, where they are inwardly curved ; anterior parallel 

 lines short ; median groove wanting, lateral groove scarcely evident or 

 wanting. All the grooves are punctate and almost lost in the rugosity 

 of the thorax. Pleurae black and evenly rugose. Scutellum black, 

 more rugose than the thorax and with short whitish hairs, the apex is 

 well rounded and at the base are two rather large opaque foveae. 

 Abdomen black, punctate and covered with short hairs. Legs: fore 

 and middle pairs brownish, hind pair black, all pubescent. Wings 

 hyaline, veins brown ; radial area almost closed ; areolet large ; cubitus 

 very faint and not extending to the first cross-vein ; second cross-vein 

 slightly infuscated and outwardly angulate. Length 2.50 mm. 



Gall.— In masses on the basal part of the midrib or petiole on the 

 underside of leaves of burr oak {Qiiercus macrocarpa) , dwarf chestnut 

 oak {Q . prinoides) , white oak {Q. alba) and other trees belonging to 

 the white oak group. They occur in rounded masses from a few to 

 about thirty in each cluster. They are closely packed together, but 

 each gall is separate and easily detachable. They are fastened to the 

 leaf by a point, rounded on top and but slightly pressed out of shape, 

 except basally. Monothalamous, almost globular, pointed basally, 

 with the surface roughened, greenish, and more or less tinged with 

 pink when fresh. Grayish when old and very hard. Hollow inside 

 with a single round larval chamber. The individual gall measures 

 from 2.50-3 mm. in diameter. The masses are from 6-15 mm. long 

 and almost as wide. 



Habitat. — Evanston, Illinois, collected by Lewis H. Weld. 



The galls occur from the latter part of August until late in 

 October, or into November, when they become mature and 

 detached from the leaf. The flies emerge during the spring 

 the following year. I have found the galls of this species 

 on Queracs alba and Q. prinoides on Long Island, New York, 

 and in New Jersey, but never succeeded in obtaining the 

 flies. The four females described above were cut from galls 

 by Mr. Lewis H. Weld, May 11, 1911. Mr. Weld's galls 

 were taken on Quercus macrocarpa late in August the pre- 

 ceding year. The name for this species was proposed by 

 the late Dr. W. H. Ashmead for specimens in his collection, 

 but which he never described. Prof. C. P. Gillette recorded 

 C. dimorpims from Michigan taken on the leaves of Quercus 

 prinus, Q. macrocarpa and O. bicolor (Rep. Mich. Bd. Agricul., 

 1888, p. 469). Ashmead's specimens were collected in 

 Florida. 



