10 DIPTERA OF NORTH AMERICA. [PART II. 



and somewhat longer. Prothorax and metathorax very coalescent, 

 with rows of bristles ; the nsual transverse suture indicated only 

 on the sides. Abdomen with seven segments, only five of which 

 are visible on the outside in the female, whereas in the male the 

 sixth segment is generally perceptible, and the seventh consists of 

 the hypopygium, usually inflected under the abdomen and com- 

 posed of two consecutive parts, bearing at the end eight paired 

 and two single appendages. Wings microscopically hairy on their 

 whole surface; auxiliary vein not running towards the anterior 

 margin ; anterior basal cell very short ; discoidal cell coalescent 

 with the second basal cell ; posterior basal cell very small ; alula 

 rudimentary ; tegulse distinct, simple, ciliated with long hairs. 



