Pupa. Length 5.0— 8. 6 mm in male pupae, 6.9— 10.6 mm in female pupae. 

 Antennae filiform, reaching end of body in male pupae, abdominal segment 5 

 in female. Labrum (Figure 648, A) curved anteriorly and laterally, with a 

 small median process; seta 1 small, other 5 setae situated close together 

 at base, strong, of equal length, anterioi- row with 2 setae, posterior row with 

 3 slightly larger setae, all 5 without hooked end; median and intermediate 

 setae of anteclypeus longer and thicker, lateral seta small, thin. Mandibles 

 (Figure 648, B) brown, slightly curved, pointed; distal part short, wide at 

 base, with median serration; basal part with a median row of small, thin 

 spinules; lateral setae situated close together, light, of equal length, short. 



Wing sheaths of male pupae reaching middle of segment 6, those of 

 female, end of segment 5. 



Midlegs with natatorial rows on tibiae and first 4 tarsal segments; setae 

 sparser on fore tibiae and tarsi. 



Posterior margin of abdominal segment 1 with narrow, posterior 

 sclerotized stripe, with blackish brown processes laterally, each with 

 3—8 large spines directed posteriorly and several smaller spines, and with 

 tubercles with spinules laterally. Holding apparatus on segments 3 — 7, 

 number of hooks: 111:2-7; IV:2-8; V:2-8+ about 60 (last number for both 

 sides); VI:3— 8; VII:3— 7. Lateral line from end of segment 5 to segment 8, 

 with thin, golden brown setae. Gills as in full-grown larva. Anal 

 appendages short, forming 2 thin, slightly curved, yellowish brown rods 

 without setae. 



Pupal case (Figure 649) 16— 18 mm long, usually much longer than pupa, 

 pupal chamber anteriorly and posteriorly with a sievelike membrane; 

 larvae before pupation adds a collarlike structure at anterior end which 

 forms a broad funnel of larger sand grains and small stones directed to 

 391 substrate; it is attached by a ligament with a disklike end; anterior and 



posterior membranes forming a brown, outer circle and a rounded, sievelike, 

 central area with 10—21 holes at anterior end, 14—30 at posterior end where 

 the membrane is larger. Case attached to moss or stones; they are often 

 found in large numbers. 



Mode of life and habitats. Microphagous; sessile, attached to 

 substrate with anterior end directed against the current, as in Brachy- 

 centrus; feeding on detritus and microscopic organisms, mainly diatoms, 

 carried by the current. 



Disti-ibution. Western border region of the European USSR. 

 In addition, Europe. 



4. Genus Micrasema McLachlan 



Full-grown larva. Small, 5.5— 9.0 mm long. Head short, rounded 

 dorsally; frontoclypeus of some species with dark anterior, and a wide, 

 dark stripe in posterior part. Pronotum relatively wide, transverse ridge 

 indistinct, in form of dark, curved stripe. Mesonotum entire in some species, 

 in contrast to Brachycentrus. Median tergites of metanotumi small, 

 pale, reduced; lateral tergites also poorly developed, with indistinct 

 boundaries. Mid- and hind tibiae without distoventral process. 



492 



