352 DIPTERA OP NORTH AMERICA. [PART II. 



first joint of their antennae distinguish them from the species of Argyra. 

 The genus Leucostola stands to Argyra in the same relation as Synar- 

 thrus does to Syntormon, that is to say, it differs from it only by the first 

 joint of the antennae being without hairs ; the considerable size of the 

 third joint of the antennae, fhe subapical position of the arista, the great 

 breadth of the antennae towards the basis, the considerable length of the 

 first longitudinal vein and its great distance from the costa, are characters 

 shared by Argyra ; most of the species of Leucostola have also, like the 

 species of Argyra, a delicate, almost silvery white tomentum, which covers 

 a considerable portion of the body. Eutarsus is very near to Diaphorus ; 

 the difference is, that the former has the third joint of the antennre some- 

 what larger and that the transverse vein is a little more removed from the 

 posterior margin of the wing ; moreover the face of the males of Eutarsus 

 is narrower, the bristles of the imbedded hypopygium are less striking, 

 the first joint of the hind tarsi is shorter, and the pulvilli of the fore tarsi 

 are, although also enlarged, not so elongated as in Diaphorus. The genus 

 Diaphorus is represented in North America by particularly varied forms ; 

 its distinction from Eutarsus has been explained above ; from Lyroneurus 

 it differs by the altogether different neuration of the wings, from Chrysotus 

 by the greater slenderness of the whole body, and especially of the feet, 

 and the comparatively longer and generally also proportionally narrower 

 wings ; moreover the structure of the head is different, as, while the eyes of 

 the males of Diaphorus are either contiguous above the antennas or at least 

 are separated by an equally broad front, those of the males of Chrysotus 

 are sometimes contiguous below, but never above the antennae, and the 

 front is always considerably widened above ; this difference in the structure 

 of the front exists also in the females of both genera ; finally, the males of 

 Diaphorus distinguish themselves by the remarkable prolongation of the 

 fore tarsi or of the fore and hind tarsi, and by the particularly striking 

 manner in which, the small imbedded hypopygium is provided with 

 bristles, which characters are not found in the species of Chrysotus ; the 

 neuration varies in the different species of Diaphorus in consequence of 

 several modifications in the position of the posterior transverse vein ; in 

 no species, however, is this vein approximated to the posterior margin of 

 the wing ; the end of the last segment of the fourth longitudinal vein is 

 sometimes cut off from the preceding part of it and pushed nearer to the 

 anterior margin of the wing, so that both parts are either completely sepa- 

 rated from each other or at least connected by an indistinct rudiment of a 

 vein, as the illustration of the wing of Diaph. interruptus shows it. The 

 genus Lyroneurus has a superficial resemblance to Diaphoru^ in the 

 structure of the body, differs, however, strikingly by the large wings, with 

 a more or less apparent greasy lustre, by the costa, which is usually 

 thickened in both sexes, or at least in the male, to a very great extent ; by 

 the end of the third longitudinal vein being strongly turned backwards, 

 and by the wide space between the fourth and the third longitudinal veins ; 

 the hypopygium is usually less provided with bristles than in the species 



