5 (3) 



6 (5) 



Operculum with 2 toothlike tubercles on posterior margin; 

 sides of tergites transversely grooved; ninth abdominal 

 segment flattened dorsal ly and emarginate at apex: Helichus 



Operculum without tubercles; tergites not transversely 



grooved; ninth abdominal segment convex dorsally 6 



Tergites with anterior margins smooth; gular sutures 

 present (Fig. 133) : 



Tergites (except pronotum) with numerous longitudinal 

 carinae arising near each anterior margin; gular 

 sutures obliterated, with 2 pairs of setae near where 



Dryops 



sutures would be: 



Pelonomus 



7 (2) Abdominal segments 1-7 each with 2 ventral tufts of 

 filamentous gills; submentum not divided; ninth 

 abdominal segment without prehensile appendages 

 bearing hooks (Fig. 135): Stenooolus 

 Abdominal segments 1-7 without gill tufts; submentum 

 divided longitudinally into 3 parts; anal region of 

 ninth abdominal segment with 2 curved prehensile 

 appendages covered with short spines 8 



Figs 134-135 Larva: 134- Anahytarsus biooloT^ left lateral 

 aspect (from Bertrand) ; 135- Stenooolus soutellarisl ^ ventral 

 aspect (from Boving S Craighead) . 



8 (7) Ninth abdominal segment with numerous fingerlike anal gills; 



apex without projection (Fig. 134) Anohytarsus 



Ninth abdominal segment with 3 median anal gills and 1 

 gill lateral to each prehensile appendage; dorsal, 

 flattened apex of ninth segment with small raised 

 projection: Anohyoteis 



56 



