and fan-shaped striations toward the mouth; face sparsely hairy, hairs longer toward the mouth; antenna quite uniformly light golden brown, only very slightly darker toward the tips, 14-jointed, hairy. Thorax: black, the pronotum, scutellum, and sides piceous or black; mesonotum smooth, shining, finely rugose laterally, with a very few, scattered, short hairs; parapsidal grooves deep, continuous to the pronotum, widely separated at the scutellum, and almost parallel; median groove very faint but extending almost one-third of the way to the pronotum; anterior parallel lines barely indicated by slight depressions; scutellum rounded posteriorly, deeply rugose, and in large part striate, the striaw distinctly converging (more so than in other species of the genus) at the ridge separating the foveæ and at the sides of the foveæ, the foveæ large, deep, shining, with a few faint cross-striations; pronotum broad, rugoso-striate; mesopleuræ rufous to piceous or black, evenly aciculated. Abdomen: reddish piceous, darker dorsally and posteriorly, entirely smooth and shining, the second segment dorsally extending over one-half the length of the abdomen, but very small in lateral extent. Legs: quite uniformly golden brown, covered with short hairs; claws toothed. Wings: entirely clear, only very microscopically pubescent; veins dark gold or light brown, without any cloudings; areolet entirely absent; cubitus extending to the basal vein; radial cell rather broad, open; first abscissa of the radius slightly arcuate, not at all angulate. Length: 1.7–2.2 mm.
Galls.—Nodular swellings of the stem (Figs. 10 and 11). Polythalamous or agglomerate, i. e., many separate cells near together in a single stem. Each swelling averages about 15 mm. long by 10 mm. in diameter, but several swellings will fuse to make one gall 7 cm., more or less, in length; it is covered with the smooth bark of the stem, but has scattered, very minute, blunt spines. The larval cells within are distributed irregularly through the pith which proliferates somewhat about the chamber, but this cell is not separable, nor is it formed of a distinct layer. On the stems of Potentilla monspeliensis var. norvegica (Linnæus) Rydberg.
Range.—Canada: Quebec (Couper); Ontario (Jarvis).
Cotypes.—Nine female and one gall cotypes in the collection of the Museum of Comparative Zoology and in the author's collection. The adults were cut from the type gall collected by Couper about forty years ago.The gall of this species was mentioned by Jarvis but the adults have not been described previously. The gall is a very simple and primitive sort of plant deformation, being more primitive than in most of the species of Diastrophus. D. fusiformans and D. fragariæ approach it in this respect. The adults are typical of the species of the genus and are readily separated by the key characters given in the description.
It is interesting to find another species of Diastrophus occurring on Potentilla. About half of the known species of that genus of gall-wasps are found on Potentilla, instead of being restricted primarily to plants of the genus Rubus as the first observations indicated. Thorough searching of the various species of Potentilla may disclose still other gall-wasps. Though tumefactus is known from only the one variety of plant, norvegica, which is confined mainly to the eastern part of Canada and the northern United States, it is possible that the same gall-wasp occurs on the typical
