sex. Three ocelli present. Antennae slender with from 

 nine to fifteen segments, clothed with short pubescence. 

 Mouth-parts elongate, females with slender, flattened, 

 elongate, saw-like mandibles, males without mandibles; 

 both sexes with slender elongate labrum-epipharynx, 

 hypopharynx, and a pair of maxillae with five-segmented 

 palpi; labium with a strong, elongate basal sclerite and 

 a pair or free, fleshy terminal lobes without pseudo-tra- 

 cheae, and with no palpi. Thorax with a distinct, broad- 

 ly interrupted transverse suture; legs moderately slender, 

 the hind pair much longer than the anterior ones, the 

 front femora of males curved in some species, tibiae with 

 or without spurs; empodia very small, almost rudimen- 

 tary, pulvilli wanting; wings broad, bare, with a mark- 

 edly projecting anal angle, and peculiarly different from 

 these of all other flies in the possession of a fine spider- 

 web like net-work of lines ('secondary venation') which 

 are the creases made by the folding of the wings in the 

 pupal stage. 



The larvae are curious, flattened, slug-like creatures, 

 legless, but provided with six suckers arranged in a me- 

 dial longitudinal row on the venter (one sucker for each 

 cf the six parts separated by constrictions of the body, 

 of which the anterior part is composed of the fused head 

 and thoracic segments, and the posterior part of the 

 fused last two abdominal segments, the other four 

 parts representing each a single abdominal segment). 

 The larvae live in swiftly running, shallow, clear and 

 highly aerated water (mountain brooks) clinging by the 

 suckers to the smooth surface of boulders or the rock bed 

 of the stream. The pupae are even more extraordinarily 

 shaped, being flat below and flatly convex above with 

 strongly chitinized, dorsal body-wall smooth and shining 

 black or blackish brown, with a pair of projecting pro- 

 thoracic dorsal respiratory horns or 'books', each com- 



