156 [July. 



are accorded due rank, or whether any of them is really entitled to 

 specific distinction. Hitherto no structural difference between them 

 has been detected ; and it is, therefore, deemed not improbable that 

 their colour-peculiarities may be the result of differences in the 

 nature of the food of the larvse. 



6. PsTCHODA HTJMERALis (Hoffmannsegg, MS.), Meigen. 



Vsyclioda huvieralis (Hoffmgg., MS.), Meig., Syst. Beschr. [*ed. i], i, 106 

 (1818) ; ? [Ps. sp. — , Westw., Introd. Mod. Class. Ins., ii, 521, foot-note, Thwaites, 

 MS., j9Mjoa (1840)] ; Rossi, *Dipt. Aust., p. 6 (1848) ; Walk., List Dipt. Ins. Brit. 

 Mus., part i, 32 (1848) ; Zet., Dipt. Scand., ix, 3707 (1850), and xii, 4887 (1855) ; 

 Meig., Syst. Beschr. [ed. ii], i, 84 (1851) ; Schiner, Fn. Aust. Dipt., ii, 636 (1864) ; 

 V. d. Wulp, Dipt., NeerL, i, 315 (1877) ; Etn., ante, 2nd ser., vol. iv, 33, step la, 

 and vol. v, pi. iv, Ps. 6 (details). — X Pericoma iullata (Hal., MS.), Walk., Ins. Brit. 

 Dipt., iii, 257 (1856). 



Wing (over black cloth and pointed towards the light) rich dark brown, with 

 bronzy and bluish reflections from the membrane, and with fringes to match ; but 

 the humeral tuft (directed longitudinally from the thickening at the base of the 

 costa), some erect hairs on the nervures of the basal cells, and the fringe of the alula, 

 very light brown ochreous-yellow ; shifted (pointing transverse to the light and 

 rocked to and fro), the fringes become glossed with a lighter tint than the disc, and 

 the bristling hair appears blackish or black-brown ; shifted again (pointing away 

 from the light nearly horizontally), the fringes match in tint with the humeral tuft, 

 and the bristling hair appears slightly darker than the smoother hair, while the disc 

 is margined either by a narrow, light-glossed line, or (as in some other postures) by 

 a narrow, dark line, set off with a light gloss externally. Over white paper, the 

 wing (in the first and last of these phases of illumination) appears thinly hairy, with 

 fringes to match, the humeral tuft alone differing in being of the original colour ; 

 shifted (costa toward the light), the greater density of the anterior fringe is very 

 apparent, and the disc is margined by a dark line, while the bristling hair is not 

 denser at the endings of the rows than elsewhere, except on the radius. Pubescence 

 on the upper part of the head and front of the thorax impure whitish, or, when 

 shifted about, yellowish-white, inclining to flaxen, matching, from certain stand- 

 points, with that on the sides of the thorax, and with the fringe of the costal callus 

 interior to the fold of deflection ; hair of the antennae, from most standpoints, darker 

 and either greyer or inclining to brown-ochre. Pubescence of the thorax elsewhere 

 denser, brown-ochreous in the dried insect, but light ferruginous-brown in the living 

 fly, matching with the dorsal pubescence of the 1st abdominal segment, and, from 

 certain standpoints, with the humeral tuft, and with the other items mentioned as 

 matching this in the above description of the wing. Indumentum of the remainder 

 of the abdomen and legs concolorous with the darker hair of the wings, approaching 

 intense burnt umber-brown in certain lights, but dark graphite-grey in others ; the 

 tips of some scales at the apical margins of the tibise and of the tarsal joints readily 

 assume a light gloss, which can be made to extend over the whole, and, when 

 suitably posed, acquires a dull silvery lustre ; the smooth hair of the abdomen, 

 especially towards the extremity, likewise shifts to the same almost flaxen tint as the 

 hair at the sides of the thorax. Length of wing, 2' to 2*25 mm. 



