246 [October. 



equally on this and the anterior pobrachial, but receding deeper on the posterior 

 pobrachial than on the postical. Beneath, at the wing-roots, are some flattened 

 hairs in both sexes. 



Antennfe {ante, 2nd ser., rol. iv, p. 31, step 2, and 32, step 4a) with the last two 

 joints of the flagellum in mutual contact ; terminal apiculus sub-claviform or obovoid. 

 Articular appendages to the flagellum, visible under a high magnifying power in 

 certain species, accumbent, hardly half the length of the joints, and distinguishable 

 from the hairs through being flattened and not spreading. 



The species can be arranged, according to the character of the 

 superior (^ genital appendages, in three divisions : — 



1st. — The said appendages as in P. palustris {ante, loc. cit., p. 120, step 2). — 

 British species, Nos. 1-3 and 12; Algerian, No. I. 



2nd. — The same appendages with a short, stout, and obtuse terminal joint, and 

 with a slender projection or spur from the under-side of one of the joints {ante, op. 

 cit., vol. V, pi. i, figs. P. 4 and 5). — British spp., Nos. 4 and 5. 



3rd. — The same appendages with a strong, elongate, and claw-like terminal 

 joint {ante, I. c, figs. P. 6a and 7a). — British spp., Nos. 6 and 7. 



1. Pericoma palustris, Meigen. 

 Trichojjtei^a palustris, Meig.,* Klaasif. d. zweifl , Bd. i, 43 (18U4) ; 

 id.* System. Beschr. [ed. i], i, 105 (1818). — Psychoda palustris, id., 

 op. cit., vi, 272 (1830), and [ed. ii] i, 83 [excluding tab. iii, 18t] 

 (1h51). — Pericoma palustris, iSchiner, Fn. Aust. Dipt., Bd. ii, 633 

 (1864) ; V. d. Wulp, Dipt. Neerland., i, 317 (1877) ; Etn , ante, 2nd 

 ser., vol. iv, 120, and vol. v, pi. i, P. 1 (neuration). 



S . Pubescence of head and body pure white, except for a slight yellowish tint 

 between and just before the wings, and a greyish tint on the metanotum. Palpi 

 brownish-black. Scape of antennae pale yellowish, with white scales, " shot " with 

 yellowish-white ; flagellum greyish-black or brownish-black, with black hairs " shot " 

 with whitish. Neuration dark throughout. Conspicuous amidst the wing-markings 

 are some black hairs in the dark median fascia for the space of about 0*5 mm. from 

 the radial bifurcation, and a smaller tuft of black prostrate hairs immediately beyond 

 the bristling hair on the axillar nervure. Beyond the aforesaid fascia, the remaining 

 bristling hairs are white ; and next to them, before the dark apical marking, a few 

 outspreading white hairs intervene, excepting on the anterior radius, where all of 

 the white hairs are apt to be bristling. The sexual diiferences in colouring are 

 extremely slight ; but the black spot at the apex of the fore tibia, anteriorly (which 

 is liable in the <? to become faint or to vanish almost completely in dried examples), 

 is more distinct in the ? , though less marked than the corresponding blackening at 

 the tips of the hinder tibiee. 



Hard to distinguish from P. gracilis in the net ; but the present 

 species is rather larger, and its more strongly marked wings give it a 

 slightly more spotted appearance. In front of the ends of some of 



t Vide sp. No. 14, P. tri/asciata, Lat., post. 



