Pronotum with characteristic, curved, transverse ridge. Mesonotum 

 of most species consisting of 2 sclerites in each half, divided by a light 

 suture. Metanotum with 2 tergites near anterior margin: a medioanal 

 sclerite close to anterior margin, and a lateral tergite. 



Forelegs short, coxa massive, femur high, tibia and tarsus short; claw 

 large, thick. Mid- and hind legs long, much longer than forelegs; femur 

 with a regular row of small spinules at ventral margin; tibia and tarsus with 

 distoventral process, only on tibia in some species; claw very long. 



Lateral line on segments 3—7. Gills on segments 2—6 and 2—7, single 

 or intersegmental with 2—7 filaments; gills sometimes absent. Anal legs 

 short, with wide area "b"; claw small, with large dorsal denticle. 



Case straight, smooth, narrower posteriorly, made only of secretion or 

 covered with small sand grains, or with regular, transversely arranged, thin 

 pieces of detritus, tetrahedral in latter case. 



Pupa. Length 6—8 mm. Body almost uniformly wide, sharply narrowing 

 posteriorly. Antennae shorter than body. Labrum rounded or narrower 

 anteriorly, anteclypeus wider. Mandibles in some species with long, thin, 

 distal part; serration fine, indistinct; distal part sometimes short. Mid- 

 tarsi with dense natatorial setae. 



Lateral line on segments 5—8. Gills as in larva. Anal rods thin, 

 slightly curved, pointed. 



Case as in larva; anterior end closed with a solid membrane with sieve- 

 like, central part with small holes; posterior membrane similar or with a 

 single central hole. 



Mode of life and habitats. Running water bodies of various types. 



Distribution. The European and Asiatic USSR. In addition, Europe, 

 Asia, North America, China, Japan. 



Key to Genera 

 Full-grown larva 



1 (2). Small, 6— 10 mm. Mesonotum with 1 or 2 sclerites in each half; 



tibiae and tarsi without distoventral tubercle or process, or tubercles 

 present only on tarsi; gills absent, rarely small and single; case 

 370 smooth, conical, made of fine sand grains, rarely of secretion .... 



4. Micrasema McL. (p. 492) 



2 (1). Length 10— 14 mm; mesonotum with 2 sclerites in each half; mid- 



tibia with large, distoventral process. 



3 (6). Length 10—12 mm; basal part of coxae with 1 or 2 dorsal rows of 



large, hooked, dark processes; femur ventrally with a row of light 

 spinules and small light setae; gills in form of small tufts; the 

 European and Asiatic USSR. 



4 (5). Head light, with dark pattern, or brownish; tarsi without distoventral 



process; case made of detritus, tetrahedral, or made of secretion, 

 brown to dark brown, with irregular tetrahedral, rarely round cross 

 section 1. Brachycentrus Curt. (p. 463) 



5 (4). Head dark brown; tarsi with distoventral process; case made of 



sand grains 3. Oligoplectrum McL. (p. 485) 



462 



