BY ARTHUR WHITE. 23 



Family VI. THEREVIDiE. 



Flies of moderate size, of elongated or conical shape, 

 the thorax and legs with distinct bristles ; distinguished 

 from the Asilidce by the eyes not being protuberant from 

 a sunk vertex, and by the head being set close against 

 the thorax, instead of being attached thereto by a slender 

 neck. Head about the same breadth as the thorax ; 

 antenna? composed of three joints, with an apical style ; 

 eyes either touching or separated in the male, always 

 widely separated in the female. Thorax distinctly longer 

 than broad, with presutural, suproalar, postalar, and 

 prescutellar bristles ; scutellum with one or two pairs of 

 marginal bristles. Abdomen either conical, or long and 

 tapering. Legs slender, rather long, with distinct bristles. 

 Wings with a venation resembling that of the Leptidce ; 

 the first posterior cell is always open, and the anal cell 

 always closed, but the fourth posterior cell may be either 

 closed or open. 



In the event of any difficulty being experienced in dis- 

 tinguishing between the Leptidce and Therevidce which 

 have a similar venation, it may be noted that in the 

 former family the thorax is quite without bristles, whilst 

 in the latter they are large and well developed. 



The division of this family into satisfactory genera is 

 somewhat difficult. Williston refers to this question in 

 his "Manuel of North American Diptera" (1908), in which 

 he states: — "Few structural differences exist, save in the 

 antennae and proboscis, and these differences seem usually 

 to have specific value only. An examination of the 

 Tasmanian forms serves merely to confirm this statement, 

 and it seems unsafe to form a genus on any single char- 

 acter. For our knowledge of the Australian forms we 

 are largely indebted to O. von Krober's "Thereviden der 

 1 ndo-Au strati sch en Region" (Entomologische Mitteilungen, 

 1912), in which a number of new genera were proposed. 

 Some of these are certainly founded on satisfactory char- 

 acters, but in other cases I am unable to appreciate the 

 distinctions, more especially in those founded on the form 

 of the antennae, a character that I consider usually to 

 be of specific value only. As an example of the unre- 

 liability of the antennae as a generic character, I might 

 refer to the two Tasmanian species of Phycus, both of 

 which are now described for the first time. (See figures 

 14 and 15.) The antennae in these two species are so 

 different that if a. classification were based on this char- 

 acter alone they might be easily placed in different genera, 

 whereas they are really so nearly allied that the antennae 



