I <, 2 NORTH AMERICAN DIPTKRA. 



more or less, sometimes much elongated; femora more 

 or less dilated, tibiae with spurs. Wings large (wanting 

 in the 9 of Epidapus}\ auxiliary vein present, though 

 sometimes rudimentary; second longitudinal vein want- 

 ing; the third vein arises from the first usually at such 

 an angle that its first section (to the anterior cross- vein) 

 has the appearance of a cross-vein; fourth vein always, 

 the third* and fifth either furcate or not ; sixth vein never 

 furcate, sometimes rudimentary; seventh vein usually 

 short, often rudimentary or entirely wanting; discal and 

 posterior basal cells always wanting. 



The family Mycetophilidae, commonly known as fun- 

 gus-gnats, comprises nearly a thousand described species 

 of small or minute flies, the best known of which are, 

 perhaps, the various dark- winged species of Sciara so 

 common about gardens. In the following description of 

 the immature stages I draw largely from Osten Sacken. 



The larvae have a distinct horny head; horny, flat, la- 

 melliform mandibles; maxillae with a large coriaceous 

 inner lobe and a horny outside piece, with a circular in- 

 cision at the tip, the labium small, horny, almost rudi- 

 mentary; the antennae are usually small or rudimentary, 

 the ocelli are Cither wanting or seen in a small pellucid 

 spot below each antenna. The body is subcylindrical, 

 more or less elongated, fleshy, whitish or yellowish, and 

 composed of twelve segments. It is smooth, without 

 hairs or bristles, except those on the ventral side. It is 

 generally transparent, showing distinctly the intestinal 

 canal and the trachea. There are eight pairs of stigmata, 

 one on the first segment, and seven on the first seven ab- 

 dominal segments, the last two having none. The loco- 

 motory organs consist of more or less apparent transverse 



i 



* I am of the opinion that the so-called anterior branch of the third 

 vein is in reality a vestige of the second vein. 



