MAY FLIES AND MIDGES OF NEW YORK 27 



ee Head widest toward the rear ; mandible with Its outer canine 

 shaped like a shoemaker's last, the heel pointing laterally 

 and the long, slender, acute toe obliquely forward; labrum 

 pendent from the flaring but notched edge of the frons ; 

 maxilla without strong teeth at tip of its lacinia and without 



long hairs on its palpus. Rhithrogena 



6& Eyes lateral ; form of body various ; claws smooth or toothed below 



Baetinae 

 c Gills completely concealed under an enormously enlarged, four- 



spined dorsal thoracic shield Baetisca 



cc Gills exposed ; thoracic dorsum 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 L e p t o p h 1 e b i a 



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 Blast urus 



gg Lamellae of each gill markedly differing in form at tip 



(see pl.8. fig.8) Choroterpes 



ee 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 

 • apieal margin of each segment beside the middorsal line 



g Head smooth above Ephemerella 



gg Head armed above with a pair of erect occipital tubercles 



D r u n e 1 1 a, gen. nov. 

 -[f 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 Chirotenetes 



ft 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 Siphlurus 



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

 tinated hooks •. A m e 1 e t u s 



ee Posterolateral angles of the hinder abdominal segments hardly 

 more than acute — not prolonged in thin flat lateral spines 

 f Gill lamellae simple 

 g Lamellae obtuse at apex ; maxillary palpus rounded at the 



apex .B a e t i s 



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

 cated Centroptilum 



