12 (10) Antennae with 8 segments, the apical one being enlarged; 



pronotum with median longitudinal groove; elytra with 



3 sublateral carinae Zaitzevia 13 



Antennae with 10 or 11 segments, usually filiform 14 



13 (12) In cold mountain streams; 2-2.5 mm long, 0.8-1 mm wide 



(Fig. 24): Zaitzevia parvula 



In a warm spring near Bozeman, Montana; 2 mm long, 0.7 mm 



wide: Zaitzevia thermae 



14 (12) Anterior tibia with fringe of tomentum (Fig. 2) 43 



Anterior tibia without fringe of tomentum 15 



Figs 24-25 Dorsal view of adult: 24- Zaitzevia parvula; 25- Ovdobrevia 

 nubifera. 



15 (14) Elytron with an accessory stria (sutural stria confluent 



with second stria at about fifth puncture) ; granules of 

 head and legs elongate; 2.2-2.4 mm (Fig. 25): 



Ovdohrevia nubifera 

 Elytron without such an accessory stria; granules of head 



and legs round (Fig . 26) Stenelmis 16 



(This section is adapted from Sanderson (1938) . In identi- 

 fication of species it will be helpful to know that in most 

 males the inner surface of the middle tibia bears a swelling 

 or row of spinules as shown in Fig. 26.) 



16 (15) From thermal waters in southern Nevada; elytra immaculate 



(5. a. aalida) or faintly trivittate (5. a. moapa) ; 

 wings reduced and non-functional; body covered with 

 dense, matted, greenish gray pile; antennae and palps 

 testaceous; aedeagus quite similar to that of S. fuscata; 

 3-3.6 mm long, 1-1.25 mm wide: Stenelmis calida 

 From east of the Rocky Mountains 17 



28 



