DERMATINA 591 



Legs strongly built and apparently adapted for slow walking purposes ; 

 femora in the Mydaidce usually spinose beneath, and the tibiae with rows 

 of small bristles, but otherwise the legs almost always without bristles 

 or pubescence except for one or more apical spines on the hind tibise in 

 some Mydaidce ; in Mitrodetics however the posterior femora bear distinct 

 pubescence. Pul villi two only ; empodium absent or represented by only 

 a thin bristle. 



Wings with a peculiar venation, very different in the two families but 



possessing one remarkable feature in common, viz., the discal vein runs 



into the wingmargin before the wing-tip. In the Scenopinidce the subcostal 



vein is very short and quite simple, but in the Mydaidce is very long and 



receives several of the subsequent veins before its tip ; in the Scenopinidce 



the prsef urea is moderately long, but in the Mydaidce extremely short ; in 



the Scenopinidce the cubital fork diverges rather widely in a somewhat 



triangular fashion, but in the Mydaidce it hardly diverges after its base 



but is long and often contracted before it ends in the subcostal vein ; in 



the Sccnoj)i7iidce the discal cross-vein is placed near the middle of the 



discal cell, but in the Mydaidce (except in Megascelus) near the end 



of that cell (as in the Nemestrinidce) ; in the Scenopinidce the discal cell 



has its lower margin entirely formed by the upper branch of the postical 



vein, but in the Mydaidce is entirely separated from the postical vein; in 



the Scenopinidce the fourth (and even third) posterior cell is entirely absent, 



but in the Mydaidce is present and forms a long conspicuous closed cell 



lying under the discal cell ; in the Scenopinidce the veins are simple and run 



comparatively straight into the wingmargin, but in the Mydaidce are looped 



and curved up in a most remarkable fashion ; in fact the venation 



exhibits two extreme contrasts except for the remarkable peculiarity 



that the discal vein (whether simple or forked) entirely ends before the 



wing-tip. The venation of the Mydaidce presents features suggestive of 



the Nemestrinidce in the exceedingly long upper basal cell and up-curved 



veins, but the similarity is probably caused by the venation being in 



both cases modified in order to secure great strength in the outer part of 



the wing, while the opposite cause has reduced the venation in the 



Scenopinidce ; a similar contrast, caused by probably the same motives, 



exists between the families of Nemestrinidce and Cyrtidoe, and in fact the 



dissimilarity of the venation of Myclas and Scenopinus is hardly greater 



than that between Ncmestrina and Acrocera. In both families of the 



Deematina the wings when at rest lie as a rule flat upon the abdomen. 



Squamae (alar) comparatively small and ordinarily with only slight fringes, 



but in the large Mydciidce fairly large and bearing a stiff coarse marginal 



fringe ; thoracal pair practically absent. 



The Dermatina are not easy to place in a natural sequence, because 

 they seem to divide the two apparently allied families of Thercvidcc and 

 Apioceridce ; there can however be but little doubt that the Scenopinidce are 

 allied to the Therevidce, especially in the embryonic stages, and that the 



