I. STRATIOMYID.E 53 



veinlet which is obsolete or missing, and usually these three veinlets run towards 

 the wingmargin without any complication, but in Xylomyinae the third veinlet 

 bends rather abruptly down and joins the upper branch of the postical vein a little 

 before the wingmargin, and thereby causes a closed fourth posterior cell ; postical 

 vein with its usual fork, and verj- easily distinguished in spite of its upper branch 

 sometimes (in the absence of the small cross-vein) forming part of the lower margin 

 of the discal cell and being sometimes {Xi/lomiiiiup) united before its tip with the 

 third veinlet from the discal cell, and in spite of its lower branch curving down and 

 becoming connected with the anal vein near or long before the wingmargin ; anal 

 cell ahvays closed : discal cross-vein always distinct and placed near or considerably 



Fig. 75. — Xtjlomijia macvlata 9 x 9. 



before the middle of the discal cell ; lower (small) cross-vein sometimes present and 

 sometimes absent ; posterior cells normally five, but when the third veinlet from the 

 discal cell is absent there are only four, all open to the wingmargin (except the 

 fourth one in Xi/Iomyimt) ; when at rest the wings lie flat on the al:)domen with one 

 wing entirely covering the other. Wing-membrane almost always ribbed or -nTinkled 

 and densely though minutely pubescent, but occasionally smooth and bare {Xemo- 

 telus, etc.), or veiy slightly uneven {Xylomyia). Squamae rather variable in develop- 

 ment ; alar pair always obvious but not at all large, and bearing a short fringe : 

 thoracal pair sometimes absent (Pachygaster, Berinw, and Xylomyince), sometimes 

 tongue-shaped (Sargiis and some CIiteUarin<v\ or sometimes large and conspicuous 

 and clothed all over the upper and under siu"faces and on the margin with dense 

 almost woolly pubescence (Stratiomys). Halteres with a rather large knob, but often 

 concealed beneath the thoracal squama? when the latter are large. 



This family would be well distiuguished from its allies were it not for 

 the aberrant Xylomyincc, as the origin of the praefurca ( = the common 

 stem of the radial and cubital veins) being almost opposite the base of the 

 discal cell is a character not shared by any other family of the Eeemoch^eta, 

 except a few CyrtidcB ; if the Xylomyince be excluded from consideration 

 it is most related to the Lcptula through the Berincc, but the Lcjytida. do 

 not have an annulated third antennal joint except in their aberrant groups, 

 and they always have at least some of the tibiae spurred, while in Stro.tio- 

 myidce the tibiae are spurred in only some species of Berince (which include 

 only one European species) ; on the other hand, in the true Leptidce the 

 wings are never ribbed or rippled and the ambient vein is continued (even 

 though thin) round the wingmargin, the cubital fork is long and even its 

 upper l^ranch does not end before the wing-tip. Consequently the only 

 difficulties lie between the Berincc and Xylomyince on the one side, and the 

 Xylophagince and Cmnomyime on the other side — omitting the exotic 

 Arthroceratince and Acantliomeridcc — and the boundary line between these 

 is not easy to define in the perfect insects, though the Berince like all 

 other Stratiomyince may be at once distinguished tln'ough the origin of the 

 praefurca being opposite the base of the pentagonal discal cell; the 

 Xylomyince may be artificially known by the closed fourth posterior cell ; 

 the Xylophagince have spurred tibiae and an open fourth posterior cell ; and 

 the Coenomyince are distinguished from all the Stratiomyidce by the long 

 boll-mouthed cubital fork-cell. 



