6> AN INTR01 \TOMOLOGY. 



TABLE OF GENERA OF THE EPHKMKKIO* OF THE 

 UNITED STATES. 



U the base of the fore wing the anal vein (a) meets the postbrachial i 

 hind tarsi, when not atrophied, have four distinct joints. 

 B. Female with the hind legs longer than the other pairs ; male with the 

 forceps-limbs sessile upon the border of the segment. 



Includes males only. Two caudal setae in both genera. 

 D. Hinder lateral angles of the 9th abdominal segment produced into a 

 short, tooth like spine. JOLIA. 



DD. Hinder lateral angles of the abdominal segments subrectangular. 



POLYMITAK 



CC. Includes females only. 



D. Two caudal setae. I C 



DD. Three caudal setae. POLYMITAKCYS. 



BB. Fore legs of females at least as long as hind legs ; male with t 

 limbs inserted at the sides of the terminal border of a short trans 

 laminar lobe prolonged from the segment. 

 C. Includes males only. 



D. Median seta extremely rudimentary. 



E. Fore leg nearly as long as body ; the tibia about ii as long as 

 femur. Segments of caudal setae well marked. External sexual 

 organs strongly hooked. HK 



EE. Fore leg about half as long as body; tibia about if asl<>: 

 femur. Segments of caudal setae inconspicuous. External sexual 

 organs nearly straight. PENTA(.I 



DD. Median seta about as long as the others. EPHEMERA. 



CC. Includes females only. 



D. Median seta extremely rudimentary. HEXAGf 



DD. Median seta about as long as the others. 



E. Abdominal segments 6-io together constituting about fof ih 



domen ; segments of the caudal setae well marked. EPHEMERA. 



EE. Abdominal segments 6-10 together constituting i of the 

 domen ; segments of the caudal setae inconspicuous. 



AA. Anal vein (a) of fore wing does not directly meet the postbrachial vein 

 (po), but is connected with it by a more or less distinct channel of circula- 

 tion in the membrane. 



B. The channel of circulation connecting postbrachial and anal veins ob- 

 solete (except in Cam's, a two winged genus). Hind tarsi with iur 

 distinct joints. 



C. Hind wings well developed; with a sharply defined, almost right-an- 

 gled projection situated at about the first \ of the costal margin. 



POTAMXXTHUS. 



CC. Hind wings of small or moderate proportions. 



D. Hind wings either gently and on the whole continuously cur 

 front, or else suddenly retracted in the middle of the fore margin. 

 E. Hind tibia usually longer than the femur, rarely subequal to it. 



