448 CYRTID^ 



but sometimes quite complete ;_ prrefurca originating almost opposite the base of 

 the discal cell ; discal cross-vein (when present) placed close to the end of the 

 praefurca and consequently near the base of the discal cell, but another cross-vein 

 analogous to the union of the cubital and discal veins in the Kemestrinidce. (fig. 251) 

 often occurs near or after the end of the discal cell, causing the presence of an 

 extra cell which can only be considered the outer portion of the upper basal cell, the 

 upper basal cell being even then only rather more elongate than in the Nemes- 

 trinidce, but these veins often become more or less obsolete until in some cases there 

 appear to be only two posterior cells ; posterior cells therefore ranging from five (of 

 which the fourth is sometimes closed) to three or apparently two only ; radial vein 

 sometimes entirely absent ; cubital fork (when truly present as in Ct/rtus, Lasia, 

 Eulonc/ms, etc.) long and normal, including the wing-tip, or with both branches 

 curving up (almost as in some Nemestrinidce) and running parallel with the wing- 

 margin until they end in the costa well before the wing- tip, but in Acrocera 

 there is a wide open spurious cubital fork of which I am convinced that the 

 lower branch is a portion of the discal vein, and then there is also a spurious 

 small cross-vein which is really the upper branch of the postical fork ; alula? very 

 variable in development, sometimes slight {Cyrtus, Pferodontm). Wing-membrane 

 very much ribbed or rippled, but apparently bare. Squamse (thoracal) extra- 

 ordinarily developed, the frenum near the angle and the squamae beyond being 

 extremely enlarged so that (when seen sideways) they stand up above the wings, 

 and the latter when at rest are depressed sideways against the abdomen ; these 

 squamae are wrinkled and usually densely hairy on the surfaces (as in some species 

 of Stratiomys), and their margin is rather strongly thickened and bears a short 

 dense fringe ; alar squamae proportionately little developed, equally siiort fringed 

 or rarely bare. Halteres covered by the enormous depressed thoracal squamae, but 

 moderate in size. 



The metamorphoses of a few species are known and are very peculiar. 

 The larvse are parasites on spiders {Arachnida) such as the Avicularidce, 

 Thcridm, and Drassidce. " Will you walk into my parlour, said the spider 

 " to the fly ? " ! Giard (BuIL Soc. Ent. Fr., 1894, cHv.) suggests that the 

 " etonnants cuillerons " serve to protect the halteres when the fly enters 

 the spider's nest. Konig (Verh. zool.-bot. Ges. Wien, xliv., 163, 1894) has 

 given elaborate details of the earlier larval stages of an Oncodes and states 

 that the young larvse have considerable springing powers. 



This family may be easily recognised by the three pulvilli, the 

 enoriiious thoracal squamae, the globular abdomen, and the humped thorax, 

 but affinities can be seen between the globular shape and that of the small 

 humpbacked Bonibylidce, and also between the venation of such genera as 

 Lasia and the Nemestrinidm. 



The Gyrtidm form a very distinct family of nearly two hundred known 

 species and about twenty-five genera, of which seven genera and about 

 thirty species have been recorded from the Palsearctic region, but at least 

 ten of those require confirmation of their specific distinctness. Only two 

 genera occur in Britain and (as far as is known) only three species, but 

 Oncodes zonafus and varius and possibly another Acrocera may occur ; 

 not one of our three species has been recorded from Scotland or Ireland, 

 nor even north of Herefordshire. They occur in all parts of the world 

 but usually as uncommon insects until their very local haunts are 

 discovered, but Osten Sacken states that they are abundant in New 

 Zealand, one species being very common there; the largest number of 

 species occur in America. 



