501 



Length of pupal case 21—2 3 mm, with a covering of small stones or 

 plant fragments arranged in all directions. Cases of small Trichoptera 

 are sometimes also used as covering material. 



Mode of life and habitats. Rivers and brooks with stony bottom. 



Distribution. West of the European USSR (rare). In addition, 

 Central Europe. 



6. Hydropsyche instabilis Curtis 



Ulmer, 1902c:467, Figures 7-9; 1 903:1 15. - Struck, 1903: 118-1 19, 

 Plate VII, Figure 2.- Siltala, 1905:105-107, Figure 24.- Ulmer, 1909: 

 235-236, Figure 361, a.- Lestage, 1921:535-543.- Philipson, 1953a:l7-23. 



Full-grown larva. Length 17 mm. Darker than the above-described 

 species, with distinct pattern. Sclerotized parts mainly yellow or yellowish 

 brown; dark parts blackish brown or black. Posterior light spot of fronto- 

 clypeus wide, with dark dots; anterior and lateral spots of same size or 

 fused; lyre-shaped figure of dorsal surface blackish brown, with dark dots; 

 ventral side with wide, dark, lateral parts; these areas usually converge 

 posteriorly; anterior part of head light. 



Labrum with a straight anterior margin. Lateral tufts shorter than in 

 H. angustipennis. Right mandible with 3 teeth in addition to apical tooth 

 on lower blade; middle tooth smaller than others. 



Pronotum dark brown or grayish brown, lighter laterally; its posterior 

 margin almost completely black or brownish inthe middle of eachhalf; dots on 

 sclerite dark. Me so- and metanotum dark brown, slightly lighter near the 

 anterior angles; dark oblique stripes and groups of dark dots; anterior 

 margin of mesonotum narrow, black, sometimes brownish black inthe middle; 

 anterior margin of metanotum brown or blackish; lateral margins of both 

 segments broad, black. Median black spot at posterior margin of meso- 

 notum connected with oblique spots of the small curves by a narrow 

 blackish or brown stripe; anterior margin of spot straight in the middle, 

 forming an obtuse angle laterally, rarely curved, but not as regularly as in 

 H. angustipennis; 6 or 7 large, dark dots near the anterior margin of 

 the spot; similar dots in areas formed by small arcs lateral to the spot. 

 Median black spot of metanotum large, serrated posteriorly, with a small 

 lateral spot. Basal seta of claw of forelegs not reaching end of claw. 



TABLE 21 



Segment 



Pleural 



Ventral 



lateral 



intermediate 



median 



Mesothorax 

 Meta thorax 



1 



2 



3 



4 



5 



6 



44 

 20 



46+36 

 40+34 

 45+35 

 36+28 

 24+19 



35+31 



22 



29 

 25 

 22 

 19 

 14 



5724 



572 



