PSE UDONE UROP TERA . 69 



F. Hind wings in front somewhat depressed in the middle. 

 G. Median caudal seta subequal to the others. LEPTOPHLEBIA. 

 GG. Median caudal seta far shorter than the others. BLASTURUS. 

 FF. Hind wing strongly angulated in front. 



G. Basal joint of forceps-limb about as long as the remainder ; 

 female with ventral lobe of segment 9 bifid and excised. 



HABROPHLEBIA. 



GG. Basal joint of foreceps-limb very short ; joint 2 longer than 

 the remainder; female with ventral lobe of segment 9 obtuse. 



CHOROTERPES. 



E. Hind tibia rather shorter than the femur. EPHEMERELLA. 



DD. Costal border of hind wings spurred or protuberant at about the 

 first \ of the wing's length. 



E. Hind wings small, and extremely narrow ; costal projection usually 

 very slender. CENTROPTILUM. 



EE. Hind wings broad, oblong, and obtuse. 



F. Hind wings with numerous cross-veins; costal projection large 



and rounded. CALLIB/ETIS. 



FF. Hind-wings with but few or no cross-veins; costal projection 



small and acute or wanting. B^ETIS. 



CCC. Hind wings wanting. 



D. With two caudal setae. CLCEON. 



DD. With three caudal setae, {fig. 640.) OENIS. 



BB. Channel of circulation connecting nerves 8 and 7 well defined ; hind 

 tarsi with five distinct joints. 



C. Space between anal (a) and first axillary (ax 1 ) veins subtended by the 

 outer half of the inner margin of the wing and the anal angle. 

 D. Tibise of the hind legs longer than, or at least subequal in length to, 

 the tarsi. 



E. Proximal joint of the hind tarsus shorter than the second joint. 

 F. Tarsal claws dissimilar ; costal dilatation of the hind wing acute. 



COLOBURUS. 



FF. Tarsal claws alike, narrow and hooked ; costal dilatation of the 



hind wing obtuse. CHIROTONETES. 



E. Proximal joint of the hind tarsus subequal to the second joint; 



tarsal claws dissimilar; costal dilatation of the hind wing almost 



right-angled, AMELETUS 



DD. Tibise of the hind legs shorter than the tarsi ; proximal joint 



the hind tarsus longer than the second joint. 

 CC. Space between anal (a) and first axillary (a* 1 ) veins subtended en- 



' ' B^ETISCA. 



tirely by a part of the terminal margin of the wing. 

 CC. Space between anal and first axiliar 

 angle and a part of the terminal margin. 



i,ii\^iy uy w. **.* G> . 



CCC Space between anal and first axillary veins subtended by the anal 



' HEPTAGENIA.* 



* The American representatives of this genus have been distributed by Eaton 

 among five genera, which are distinguished by such slight and inconstant variations 

 in structure that I have been unable to express them in a tabular form. 



