MAY FUKS AND MIDGES OF XK\V YdKK 27 



66 I lend widest toward the rear; mandible with Its outer canine 

 shaped like a shoemaker's lust, the heel pointing lalenilu 

 and tlie Ion-, slender, aeute toe obliquely forward; lahnim 

 pendent from the ilaring but notched edge of the irons ; 

 maxilla without strong teeth at tip of its lacinla and without 



long hairs on its palpus R h i t h r oge n a 



bb Kyes lateral: form of body various; claws smooth or toothed below 



Baetinae 



o Gills completely concealed under au enormously enlarged, four- 



spiued dorsal thoracic shield B a e t i s c a 



(Jills exposed; thoracic dorsuin normal 

 d Outer caudal setae fringed on both sides 

 e Gills on abdominal segments 1-7, double 

 f Gills filamentous 



g Each a pair of simple filaments Laptop hlebia 



gg Each a pair of clusters of slenderer filaments 



Habrophlebia 



ff Gills lamelliform, at least on the middle segments 



g Lamellae of each gill similar B 1 a s t u r u s 



gg Lamellae of each gill markedly differing in form at tip 



(see pl.S. fig.S) Choroterpes 



ce Gills absent from one or more of segments 1-7; one pair more 



or less elytroid, covering those behind it 



f Gills present on the seventh abdominal segment, elytroid on 

 the third or fourth segment; a pair of tubercles on the 

 apical margin of each segment beside the middorsal line 



g Head smooth above E p h e m e r e 1 1 a 



gg Head armed above with a pair of erect occipital tubercles 



Drunella, gen. nov. 



ff Gills absent from the seventh abdominal segment, elytroid on 

 the second segment; no dorsal abdominal tubercles 



C a e n i s 

 dd Outer caudal setae fringed only on the inner side 



e Posterolateral angles of the hinder abdominal segments pro- 

 longed into thin, flat, sharp lateral spines 



f Fore legs conspicuously fringed with long hairs; gill tufts 

 present upon the bases of maxillae and front coxae and at 



bases of lamellae on abdomen Chiroteuetes 



ff Fore legs without conspicuous fringes ; no maxillary or coxal 



gills ; no gill tufts at base of lamellae on abdomen 

 g Gills double on the basal abdominal segments; end of max- 

 illa fringed with simple hairs S i p h 1 u r u s 



gg Gill lamellae all single; end of maxilla fringed with pec- 

 tinated hooks Ameletus 



ee Posterolateral angles of the hinder abdominal segments hardly 



more than acute not prolonged in thin flat lateral spines 

 /" Gill lamellae simple 

 g Lamellae obtuse at apex; maxillary palpus rounded at the 



apex Baetis 



gg Lamellae acute at apex ; end of maxillary palpus trun- 

 cated Centroptilum 



