122 [June, 



Museum (Nat. Hist.) possibly belongs here ; but this is doubtful, 

 since the species has not yet been met with in northern Africa. Faded 

 specimens of Ps. humeralis in windows are liable to be mistaken for 

 phalcenoides, if the distribution of bristling hair on the wing be 

 disregarded. When the wings are denuded as well as the body, a 

 difference in the gait of the flies, and in the form of the verticils of 

 hair of the antennae, suffice for their distinction. 



The females of Ps. pTialwnoides are common agents in the ferti- 

 lization of Arum maculatum, L., creeping down into the spathes, often 

 in considerable numbers, when the pollen ripens. Once at the bottom 

 they have to remain until the sterile filaments wither and set them 

 free. Meanwhile, through fluttering and tumbling about, they soon 

 become miserable objects denuded of hair, and many perish. The 

 dead are usually eaten by other insects, and by Oniscidce. Where 

 Curtis speaks of Ps. nervosa sometimes swarming about drains (loc. 

 cit., 1849), there may have been some confusion of the species with 

 Ps. sexpunctata, seen with the naked eye.* 



3. PsTCHODA ALBiPENNis, Zetterstedt. 



Ps. albipennis, Zet., Dipt. Scand., ix, 3708 (1850) ; Schiner, Fn. Aust. Dipt., 

 ii, 637 (1864) ; v. d. Wulp, Dipt. Neerland., i, 315 (1877) ; Etn., ante, 2nd ser., 

 vol. iv, 130, step 3a, and vol. v, pi. iv, Ps. 3 (details). 



Similar to Ps. phalcBnordes, but, sex for sex, on an average smaller. Easily dis- 

 tinguished by difPerences in the $ genitalia, illustrated in loc. cH. from a dried 

 preparation ; for comparison with the superior appendages of freshly killed speci- 

 mens, the upper fig., Ps. 3a, is the best. Inferior appendages much the same as in 

 the former species. 



? Hardly separable, when faded, from dried specimens of Ps. phalcenoides of 

 this sex ; but when in prime condition, newly killed, and correspondingly illuminated, 

 the wings appear whiter ; the costal fringe and the tuft of hair on the thickened 

 portion of the base of the costa, by which the fringe thereabouts is overlain, do not, 

 on being shifted about, assume quite so dark a grey tint as in that insect ; the callus 

 nearer the base of the costa is of a lighter colour ; and the fleshy parts of the body 

 beneath the hair are of rather a light colour, although (like the callus) often quite 

 as dark when dried. Besides what is said about the wing-neuration in the explana- 

 tion of the figures cited, given in op. cit., vol. v. 27, it is noteworthy that the 

 variations illustrated are independent of sex, and that the radial fork is sometimes 

 as short as in the fig. Ps. 1, loc. cit. Both species are liable to be represented in 

 collections of Diptera by females exclusively, no doubt through these being larger, 

 and therefore easier to pin than males. 



A species of wide foreign distribution, abundant in England, and 



* It may be stated here, once for all, that the bibliographical references to old authors given 

 in this article under the head of particular species are limited each to the author cited, and do 

 not extend to his citations of earlier authorities. It would demand more space than the matter 

 is worth, to note every instance where the synonymy of paleeographic entomology is at fault. 



