362 MEDICAL ENTOMOLOGY 



(macrochaetae) ; Humeral 3 ; posthutneraJ 1 ; notopleural 2 ; presutural 

 1 ; supra-alar 1 ; intra-alar 1 ; post alar 2 ; dorsocentral 4 or 5, usually 

 one small one in front of the suture; acrostichal 2; tnesopleural 12; 

 sternopleural 7, arranged 0:1. Abdomen usually marked with a dorsal 

 stripe, bands and spots. Wings grey, sometimes tinged with yellow ; 

 fourth longitudinal vein with a looped curve, gently bending upwards 

 to its extremity ; first posterior cell broadly open. 



The flies belonging to this genus are chiefly found in Asia and Africa, 

 though calcitrans is now almost world wide in its distribution. Most of 



... . . them are extremely difficult to identify, as no two 

 Identification of . 



Species specimens have exactly the same markings, and what is 



worse, the spots and bands vary according to the light 

 in which they are examined ; thus calcitrans has been described no less 

 than seventeen times under different names. Miss Summers, who has 

 recently studied the Oriental species, states that the characters most 

 to be relied upon are: (1) The width of the frons in relation to the 

 width of the head ; (2) the width of the light median band on the thorax 

 and (3) the colour of the legs. The abdominal markings are not reliable 

 taxonomic characters, and should not be wholly used in distinguishing 

 the species ; calcitrans is a good example, as it shows great variation in 

 this respect. Miss Summers recommends tracing the outline of the head 

 and the median thoracic band with a camera lucida, using a low object- 

 ive and eyepiece, ' and measuring the drawings. She gives the following 

 key for the identification of the more important Oriental species : 



A. Legs mainly black 1 



B. Legs mainly brown 2 



1. Frons in male wide, one-quarter, or one-fifth width of head .... 3 



Frons in male narrow, one-eighth or less width of head. 



Abdomen with round spots sitiens (Male). 



3. Dorsal stripe on thorax narrow ('35 mm.) at anterior end, 



widening towards the posterior end. Abdomen spotted .... 4 

 Dorsal stripe on thorax wide ('75 mm.), uniform in width. 

 Abdomen banded ........ nigra. 



4. Spots round calcitrans. 



Spots triangular, apex pointing to edge of segment . . triangularis. 

 Spots elongate oblongopunctata. 



B 



2. Frons wide, one-quarter to one-fifth width of head S 



Frons narrow, one-sixth to one-eighth width of head . . ... 6 



5. Abdomen distinctly banded 7 



