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BRITISH FLIES 



which form rows of spicules and an apical rosette on the 

 tibiae. VIII. Therevid^:. 





Fig. 44. — Thtrevu luihililu'a c5 . x 4. 



The Tlierevida are moderate-sized flies, which have a conical 

 tapering abdomen some-\vhat like that of the Leptidte but clothed with 

 furry pube.scence. They are the first family of the Brachycera to 

 show conspicuous chaetotactic bristles, and the ovipositor of the female 

 is armed with a rosette of spines like many of the Mi/da i the and 

 Asilidce. 



17 (14) Pedestrian species, usually armed with strong bristles and only 



occasionally (Laphria, Isopogon, etc.) clothed with dense coarse 

 pubescence, or (Dekmatina) bare of both pubescence and 

 bristles. Legs strong, usually armed with strong bristles on 

 at least the tibise and tarsi. Eyes almost always widely 

 separated in both sexes ( = dichoptic), and frequently bulgin 

 out from the deeply sunken vertex. 



18 (21) Eremochcetous species in the sense that there are no strong 



bristles on any part of the thorax or scutellum. 



DERMATINA. 



Usually dark rather leathery-looking species without any bristles 

 or pubescence except sometimes some pubescence on the head, sides of 

 the mesonotum, and basal corners of the abdomen, but there may be 

 spicules on the tibite, strong serration beneath the hind femora, and 

 sometimes one or more apical spurs or spines on the hind or even 

 on all the tibiae. Antennae with the thii-d joint either elongate 

 without a style or arista {Scenopinidce), or with an apical style which 

 is developed into a (usually) long-jointed club {Mydaidce). Venation 

 with the main ( = upper) branch of the discal vein ending before 

 the wing-tip ; posterior cells three to five. Very large to rather small 

 species. 



The two families composing the Dermatina are at first glance very 

 dissimilar, but closer study shows that they have many important 

 characters in common. The total absence of thoracic bristles and the 

 discal vein ending before the Aving-tip are (luite sufficient characters 

 to distinguish them from all others. 



