anterior part. Posterior median tergites smaller, triangular, with short 

 setae; lateral tergites oblong, pale posteriorly, dark anteriorly, with black, 

 short to moderately long setae. Groups of setae between tergites 

 (Figure 549, A). 



Prosternite in form of small, median sclerite. Horn thin. 



Legs like those of D. c au c a s i c u s. Forelegs much shorter and more 

 massive than others; midlegs longer than hind legs. Fore femur with a row 

 of small spinules at ventral margin; primary ventral setae in form of 

 2 large, light spines; similar 2—5 secondary setae situated among small 

 spinules; posterior primary seta black, short, strong, situated basally 

 (Figure 550). 



Number and arrangement of gills of D. trifidus (after Klapalek) 



Segment 



Dorsal 



Pie 



ural 



Ventral 



2 







1 



1 

 1 



3 





1 



1 



1 

 1 



4 





1 



1 



1 

 1 



5 









1 

 1 



6 









1 

 1 



7 









1 

 1 



Abdominal segment 1 wider than other segments; dorsal and lateral 

 processes large, setae between them short, strong; ventral side of segment 

 with median convexity, with short, black setae, and 2 small sclerites close 

 together on median side; a small sclerite and a group of setae, one of them 

 on sclerite at base of lateral process. 



Lateral line from beginning of segment 3 to beginning of segment 8 with 

 thin, very small hairs. Gills on segments 2—7. 



Tergite of segment 9 brown; median setae, intermediate setae, anterior- 

 angle setae, and secondary seta between medioanal setae long, thick, black; 

 anterior-angle setae slightly larger than others. 



Sclerite "b" of anal legs dark, 3 long, thick, black setae on membrane 

 dorsally near posterior margin; several thick, moderately long setae at 

 median margin; surface with a group of shorter and smaller setae. 

 Sclerite "c" in form of a short, wide triangle with a black marginal stripe; 

 seta small, strong, dark. 



Claw dark, short, black or blackish brown apically, with a large, dorsal 

 denticle; dorsal seta 2 moderately long, larger than others. 



Mode of life and habitats. Clear brooks and sources. 



Distribution. Western and southwestern parts of the European USSR, 

 especially in the Carpathians. In addition. Central and Southern Europe. 



398 



