1864.] 607 



low, irregularly hemispherical, greenish yellow gall, .02 — .04 inch in diameter, 

 mostly on the upper side of the leaf, and often, but not always, with a pointed 

 nipple on the middle of the hemisphere, always with a corresponding circular 

 depression on the other side of the leaf, in the middle of which is a very minute, 

 flattish hemisphere. Very frequently on one and the same leaf the position of 

 the gall is reversed from the ujjper to the lower side, as in Q. pihiloe Walsh. 

 On a single leaf scores of them may often be counted, generally with several 

 masses among them, composed of two or more confluent galls. Commences its 

 growth early in the summer, and by the last of August many are found to be 

 burst open at top, yet at the same time very many of them, when opened, are 

 found to be solid without any central cell. By November most of the galls 

 from which I attempted to breed the insect had burst open into a ragged, wart- 

 like shape on the hemisjiherical side, but no larvte had escaped from them and 

 none were discoverable in them. As the leaves were kept too moist, so that 

 they moulded badly, the larvae had probably perished in the galls. 



Described from 20 affected leaves. From its close homology with 

 the much larger oak-galls St/mmrtrk-a 0. S. aqd Q. pilulse Walsh, iu 

 the former of which Cecidomyidous larvae were detected by Osteu 

 Sacken, and described (Dipt. X. A. p. 201) as having a Y-shaped breast- 

 bone, and in the latter of which I found myself, September 14th, 

 several orange-colored larvje, which, from the presence of a clove-shaped 

 breast-bone, were undoubtedly Cecidomyidous, and from the fact of a 

 similar leaf-gall on a Willow, *S'. verruca n. sp., being inhabited by a 

 Cecidomyidous larva, there can be no doubt, I think, that the gall S- 

 semen is the work of a Grall-gnat. Prodigiously abundant and very 

 common everywhere in Rock Island County, Illinois, on the Black 

 Willow, the foliage of whole trees being thickly frosted over by it, so 

 that the leaves look like nutmeg-graters. I have in a cursory manner 

 noticed in July several specimens of what seemed a very similar gall ou 

 S. discolor, but found no larva) in them ; and in a single instcince I 

 found, August 20, two leaves of S. longifolia on a twig which grew out 

 of a bunch of the galls S. brassicoides, covered so densely with some- 

 what similar galls as to be intermediate in appearance between S. se- 

 men and *S'. penigma. On August 29 I discovered in one of the cells 

 of this gall a minute, pale-colored, apod larva with a large, scaly head, 

 and the disk of its dorsum, but not of its venter, fuscous. This so ex- 

 actly resembled a much larger larva of which I have found many spe- 

 cimens in the Cecidomyidous gall, Q. pilidx Walsh, and which I am 

 sure, from comparing it with the larva of Anthonomus scutellatus Schonh., 

 must be Curculionidous, that I believe it to be also Curculionidous, 



