1. THEREVA 547 



3 (4) Pubescence wholly bright tawny (black hairs may be traced with 



difficulty down the mid dorsal line of the abdomen, and incon- 

 spicuous thin black liairs occur all about the disc of the thorax, 

 besides the usual strong black bristles). Prsescutellar bristles 

 in two pairs. 1 fulva. 



4 (3) Pubescence obviously considerable mixed with black or at any rate 



not wholly bright tawny. Prsescutellar bristles normally in 

 one pair (except sometimes in T. arcuata). 



5 (6) Abdomen mainly jet black with bands of bright tawny pubescence. 



Tarsi ferruginous at the extreme base only. Prsescutellar 

 bristles sometimes in two pairs. Fourth posterior cell often 

 just open. 2 arcuata. 



6 (5) Abdomen not jet black with bands of bright tawny pubescence. 



Tarsi considerably ferruginous at the base. 



7 (8) Abdomen and thorax with mainly black or dark brownish yellow 



pubescence. Pubescence on the face and jowls extensively 

 black. Bather large species. 5 circumscripta. 



8 (7) Abdomen and thorax with considerable obvious tawny or greyish 



yellow pubescence. Pubescence on the face and especially the 

 jowls not extensively black. Medium-sized species. 



9 (10) Abdomen with pale ventral and black dorsal pubescence, and the 



pale pubescence not extending beyond the sides. 4 plebcia. 



10 (9) Abdomen with the pale ventral pubescence extending over the 



sides and to a considerable extent on to the disc. 



11 (12) Ground colour black. Abdomen rather narrow and elongate. 



2 arcuata. 

 var. inornatOj. 



12 (11) Ground colour brownish black. Abdomen wider at the base and 



apparently less elongate. 3 noUlitata. 



13 (2) Pubescence of abdomen mainly whitish grey or pale yellowish 



grey. Smallish species. Wing-veins very intense. Pree- 

 scutellar bristles in one pair. 6 Mpicnctata. 



14 (1) Pubescence silvery white. Prsescutellar bristles (normally) in 



two pairs. 



15 (16) Halteres blackish. Pourth posterior cell usually wide open. 



7 lunulata. 



16 (15) Halteres whitish. Fourth posterior cell closed or almost so. 



8 annulata. 



Table of the Females. 



1 (12) Frons with a shining black callus or pair of spots. 



2 (11) Frontal callus (normally) entire. Seventh abdominal segment 



with short rigid black hairs. 



3 (4) Almost wholly tawny species. Prtescutellar bristles in two pairs. 



1 fulva. 



