NORTH AMERICAN HYMENOPTERA. 61 



though in a few the stem is half an inch long. The upper half of 

 the gall is covered with a thin, white, papery epidermis, which is 

 usually torn and curled by the rapid growth of the gall itself. 



The true bark beneath is red or brown, and quite smooth in fresh 

 galls, but wrinkled when they become dry. The apex of several 

 galls is crowned with sharp spines and such are found on the base, 

 and stem of others. It is plain that each gall is a foreshortened 

 branch and the gall-fly must lay her eggs in it at an early stage of 

 its development. These galls are polythalamous. 



Gall-flies. — Male and female. 9- — Head black; antenna} black, first joint 

 ovate, second globose, third twice as long as the fourth, which slightly exceeds 

 the remaiuiug ones. Thorax black, finely and evenly rugose or wrinkled, shin- 

 ing rather than dull, jiarapsidal grooves very fine, two short parallel lines on 

 the anterior half of mesonotum and a short median line on the posterior half 

 of the same and a smooth, shining ridge over the base of each wing; pleurae 

 rough, scutellum evenly rough or rugose. Abdomen very dark reddish brown, 

 approaching black. Legs the same color. Wings with a yellowish tinge througli- 

 out, but deeply clouded on the veins that bound the radial area, and indistinctly 

 so beyond its apex; veins distinct, except that the slender cubitus is scarcely 

 discernible at its union with the first transverse; areolet large, and the veins 

 bounding it of equal size. Length of the body .12 inch. 



%. — Black, except the abdomen and legs; these are darkei-, however, than 

 tho.se of the female. Wings subhyaline, with no cloudiness, except that along 

 the veins bounding the areolet and the radial area. The yellowish tinge that 

 pervades the wings of the female appears here, and is rather more intense than 

 in that sex. Abdomen very small. Length of the body .10 inch. 

 3. R. variabilis n. sp. 



Galls. — Irregularly rounded, sometimes ovate or reniforni, and 

 varying so much in form and size as to make a description difiicult. 

 They are from one-quarter to three-quarters of an inch in diameter 

 in the more regular forms, but the reniform specimens often exceed 

 an inch in diameter. Polythalamous, but evidently so through the 

 perfect coalescence of two or more galls. The surface, like that of 

 a russet apple and the color, nearly the same. Some, gathered per- 

 haps before they were fully matured, are of a darker color, and are 

 shrunken. These last may possibly prove to be a distinct species, 

 but the insects offer no essential points of difference. 



The development of these galls is as variable as their form. Some 

 appear to grow on the ends of the small branches, others are at- 

 tached to the leaf stems, while others are developed from an abor- 

 tive leaflet, while still others grow on the surface of fully developed 

 leaves. Internally, they ai-e of a rather solid, pith-like substance, 

 and the larva? have no free larval cell. 



