THE CANADIAN ENTOMOLOGIST. 247 



j. Claws of each tarsus alike; caudal 

 seta' at least one-half longer than 



body Siphloniirus. 



jj. Claws of each tarsus unlike; caudal 

 setae about as long as the 

 body Ameletus. 



Nymphs. 



e. Postero-lateral angles of the hinder abdominal segments pro- 

 longed into thin flat sharp lateral spines, 

 f. Fore legs conspicuously fringed with long hairs; gill-tuft 

 present upon the bases of maxilhe and front coxae and 



at bases of lamellae on abdomen Chirotenetes 



ff. Fore legs without conspicuous fringes; no maxillary or 



coxal gills; no gill-tufts at bases of lamellae on abdomen. 



g. Gills double on abdominal segments 1-3; claw of 



fore tarsus flattened and bifid ; terminal segment 



of labial palpus wanting..... SipJilopJecton. 



gg. Gills not double on abdominal segments 1-3; claw 

 of fore tarsus uncinate; labial palpus normal, 

 h. Abdominal segments with broad lateral ex- 

 pansions; mid-ventral meso- and meta- 



thoracic spines Siphlonisca. 



hh. Abdomen without such broad lateral ex- 

 pansions and thorax without ventral spines 

 i. Gills double on the first two abdominal 

 segments; end of maxilla fringed 



with simple hairs Siphlonnrus 



ii. Gill lamellae all single; end of maxilla 

 fringed with pectinated 

 hooks Ameletus 



Key to the Species of Siphlonnrus. 

 Imagos. 

 a. Wings clear, without clouded areas. 



b. Venter with brown stripes, dots and 



streaks S. alternatus. 



bb. Venter with U-shaped brown marks 5. occidentalis. 



bbb. Venter with triangular brown marks 5. triangularis. 



