INTRODUCTION. XVII 



Labrum Paraglossa. 



Hypypharynx. . . . Ligula. 



Mandibles Lacinia. 



Maxillse. .... Palpifers. 



Maxillary palpi. . . . Maxillary palpi. 



Labium. .... Galea. 



THORAX. 



The thorax is composed, as in other insects, of three parts, 

 the ^r-o-thorax, the meso-thorax and the meta-thorax, but the 

 first and the last are so aborted as to present but few ana- 

 tomical characters. The prothorax is perhaps most readily 

 distinguished in the Nematocerous flies, forming a rounded 

 collar back of the neck. The metathorax is not seen at all 

 from above ; the scutellum, cut off by an impressed line, usu- 

 ally a semi-oval body, really belongs to the mesothorax, the 

 dorsum of which is often called the mesonotum. 



Transverse suture, an impressed line usually running 

 straight across the mesonotum and terminating a little in front 

 of the root of the wings. It is more or less incomplete in 

 the middle. 



Humerus or humeral callus, the anterior superior angles of 

 the mesothorax, usually a more or less rounded callus. 



Post-alar callus, a more or less distinct rounded swelling, 

 situated between the root of the wing and the scutellum. 



Pre-alar callus, a similar, but usually less prominent, pro- 

 jection situated before the root of the wings on the sides of the 

 mesonotum, just back of the outer ends of the transverse suture. 



Scutellar bridge, a small ridge on either side of the scutel- 

 lum, connecting it with the mesonotum. 



Presutural depression, a depression, usually triangular in 

 shape, at the outer ends of the transverse suture, near the 

 dorsopleural suture. 



Supra-alar groove, a groove on the mesothorax immediately 

 above the root of the wings, along the inner margin of which 

 there are, usually, characteristic bristles. 



