Orthorrhapha Brachycera. 369 



waini, dry, alniost rainless, climate. (Central Asia, South Kastern 

 Euro])o, some parts of Africa, of Australia and the deserts of South 

 Aniei'ica.) [Compare in Berghaus's Physic. Atlas, new cdit.; thc 

 map Meteorologie, N°_ XI (1886) has areas tinted in the palest bluo, 

 indicating a miniinum of rainfall; those are the regions of the Ne- 

 mestrinidae.] 



As I Said above, the prevalence of holoptic heads in the male, 

 connected with the power of hovering, and logs, üt principally for 

 alighting, distinguish the Tromöptera. Dichoptic heads in the male 

 occur only exceptionally. The number of posterior cells as a maxi- 

 mnm is five in the Cyrtidae and Nemestrinidae and four in the 

 Bomhylidae. Bnt as the venation in all these families is vcry 

 variable, and subject to degradation, this is not a very deep-seated 

 character. The number of pulvilli is normally three in the Cyrti- 

 dae and Nemestrinidae, and in this, just as in the number of poste- 

 rior cells, they approach the Uremochaeta. Whether this double 

 coincidence is an index of some hidden relationship is as yet unknown. 

 The Bomhylidae are a mnch more numerous family than the 

 two just mentioned ones, spread almost universally, but always see- 

 king dry and sunny situations. ') The variety of forms in this family 

 is unique among Diptera: Boml>ylii(S, Aiithra.v, Lomaiia are the 

 principal types, showing a more or less distinct System of macro- 

 chaetae, cspecially on the sides of the thorax (Boinhyliiis on the 

 ubdonien, concoaled vvithin a dense clothing of für). The extremes, 

 OS to form, are the slender Systropus, outirely bare of hairs or brist- 

 les, and the heavy Toxophora. with comparatively small wings, but 

 stout legs, and showing an unusual devclopment of stout macrochaetae 

 on the thorax, and even a pair of ocellar bristles on tho liead (a 

 unique case, I believe, among Tromöptera), almost a pedcstrian 

 among aerial Diptera! Among all this variety of forms, howcver, the 

 parasitism of the larvae is a constant character. 



1 have no hcsitation in placing the Therevidae among the Tro- 

 möptera, but T would consider them as an ancestral form. I de- 

 rive this opinion from the fact that species of this family are appar- 

 ently common in New-Zealand (which, as well known, abounds in 

 non-evoluted forms, as Dr. D. Sharp calls them in bis paper on 

 N.-Z. Coleoptera). All coUections from N.-Z. contain Therevae, and 

 the earliest Dipteren described (1775) from these Islands was 2\ hi- 

 lineata Fab., collected by Sir J. Banks, companion of Capt. Cook. 



^) The silvery hoariiiess whicli so oftcn occurs on Diptera liviiig 

 in damp situations, like tlie TJoUcIlopodldae, Epliydridae etc. is 

 never scen on Bomhylidae. 



xrj. Heft IV. 24 



