F. R. COLE 17 



placed in a web with two spiders and was approached warily but 

 not touched. It may be that all spiders would not show such 

 consideration for this fly. It would be reasonable to suppose 

 that it would arouse fear in only those spiders which were par- 

 asitized by it. 



In the case of Pterodontia flavipes the period of incubation was 

 recorded by King as thirty-two and thirty-three daj^s, the larvae 

 emerging from a lid-hke opening at the pointed end of the egg. 

 These first stage larvae are campodeiform, dark brown or black 

 in color and about 0.25 mm. long, the body composed of twelve 

 segments including the head. The caudal end of the eighth 

 ■ abdominal segment has a sucker or disk which serves for attach- 

 ment. On each side of the caudal disk is a long stiff spring- 

 bristle used in leaping. There are no spiracles. On the cau- 

 dal margin of the eighth segment are two crescentic areas 

 resembling spiracles; these are notches in which the caudal setae, 

 or spring-bristles, rest when the larva stands erect. The larvae 

 are quite active, particularly at night, and leap five or six milli- 

 meters. They crawl by extending and contracting the body seg- 

 ments. 



Classification 



Key to the Subfamilies 



Prothorax abnormally enlarged and meeting above in front of the mesonotum. 

 Wing venation more or less complete, but never complex, and the cross- 

 veins may be lacking. Proboscis short or moderately long, never entirely 

 aborted. Abdomen never abnormally inflated, in some cases rather slender. 

 Tropical species Philopotinae 



Prothorax normal, not unusually developed. Third antennal joint long, often 

 laterally compressed; North American forms, except Pialeoidea, with no 

 apical arista or hair-like raj^s. Venation complete, often complex. Probos- 

 cis short or long, in some species longer than the body Panopinae 



Prothorax not unusually developed. Wing venation often much reduced. 

 Anteiuiae small, inconspicuous, and with a terminal arista or hair-like rays. 

 Abdomen usually swollen in appearance or balloon-shaped Cyrtinae 



Table of North American Genera 



1. Prothfl^ff^ic lobes greatly enlarged, meeting in front of the thorax. Pro- 



boscis elongate Philopota 



Pre ■^acic lobes not forming a shield in front of the thorax 2 



2. Pr6 juscis small, aborted 3 



Proboscis elongate 9 



TRANS. AM. ENT. SOC, XLV. 



