2G0 Benj. D. Walsh on the Insects inhabiting the Galls 



4th. The collare is black, except a pale line on its superior margin which is pro- 

 longed downwards under the wing on its hind margin. 5th. The lateral plates 

 of the abdomen are black as in 9> bui the venter does not appear to be tipped 

 with black as it does in 9> because in this sex the lateral plates do not conceal 

 its tip. Length % .It — .13 inch; front wing % .13 — .14 inch. 



Two % , three 9 > bred April 27 — June 9. Distinct from the nor- 

 mal S. pomum % 9 an d S. desmodioides % o by the darker colora- 

 tion of the body % 9 > and S from S. desmodioides % by the flagelluni 

 being pale below, which seems a pretty constant character in this fami- 

 ly. From an undescribed, cabbage-like, polythalamous, Cecidomyidous 

 gall on the White Oak ( Q. brassica Walsh MS.), the structure of which 

 is analogous to that of Gecidomyia solidaginis Loew, I bred, May 18 

 — June 10, 2 % 7 9 °f an inquilinous species — Nematus quercicola, n. 

 sp. — which cannot be distinguished from the galhnaking N. s. pisum % 

 9 . The habits, however, of the two insects differ remarkably in other 

 respects also. For all my N. s. pisum went underground to pupize, and 

 all my N. quercicola pupized in the gall. From certain described spe- 

 cies N. s. pisum may be distinguished in the same manner as N. s. 

 pomum. In the 9 venter being pale and apparently tipped with black 

 from the blackness of the lateral plates, the 9 agrees with Nem. corni- 

 ger 9 Nort., the % only of which species has been hitherto described, 

 and differs from all other 9 Nematus known to me, with the exception 

 of Nem. quercicola, n. sp. We find the same character in Euura s.- 

 (jemma, n. sp. In a single % the 3rd submarginal cross-vein is repre- 

 sented only by a stump. 



Genus NEMATUS.-— Inquilines or Guest-flies. 

 Nematus inquilinus, n. sp. — 9 Shining honey-yellow. Head with the eyes, 

 a quadrate spot enclosing the ocelli, not near attaining the antennse, and sepa- 

 rated from the eyes by a pretty wide orbit, and also the tips of the mandibles, 

 all black. Clypeus emarginate in a circular arc of about 120°. Labrum promi- 

 nent and rounded at tip. Occiput generally with a discoidal black cloud. Ar*- 

 tennre full h as long as the body, joints 3 — 5 subequal, 6 — 8 slowly shorter and 

 shorter, 9 as long as 8, the scape black, the flagelluni brown-black. Thorax 

 with a broad vitta on the anterior <? of the anterior mesonotal lobe, sometimes 

 reaching to the scutel, the whole of the lateral lobes, or sometimes only the in- 

 terior ^ of each, the extreme base and tip of the scutel, with sometimes a black 

 line connecting the base and tip, the entire pectus, and part of the pleura, so as 

 to leave above a large triangular honey-yellow spot of variable size, and a cloud 

 on each lower angle of the collare, all black. Metanotum black, the basal plates 

 occasionally with a discoidal honey-yellow cloud on each side. Cenchri whit- 

 ish. Dorsum of the abdomen black, sometimes on all but the last joint, some- 

 times on two or three of the basal joints only, with two or three of the following 

 sutures dusky, sometimes only on the base of joint 1 with three or four of the 

 following sutures dusky. Lateral plates honey-yellow. Cerci honey-yellow 

 lipped with dusky. Basal membrane yellowish-white. Ovipositor yellowish- 



