314 REV. A. E. EATON ON EECE^^T EPHE5IER1D.1; OR MAYFLIES. 



if there are more tban two intercalar nervures, that 

 which is next to the Anal (8) nervure is long. Lobe of 



the 9th ventral segment of $ obtuse 29 



If there are more than two intercalar nervures 



in the said interspace, that which is next to the Anal 

 (8) nervure is short or rudimentary. Lobe of the 9th 

 ventral segment of $ bifid and acutely excised 30 



29 .... Basal joint of the cJ forceps-limb very short ; 2ud 



joint by far the longest Churoterpes (p. lOi). 



Basal joiiit of the 6 forceps-limb by far the 



longest Thraulus (p. 106). 



30 • • . . Basal joint of the s forceps-limb nearly as long 



as the remainder of the limb Rabrophlehia (p. 114). 



Basal joint of the 6 forceps-limb longer by far 



than the remainder Calliarcys (p. 121). 



Ephemerella Type. 



31 .... Median caudal seta long. Hind wing well pro- 

 portioned, and with copious neviration : subcosta arched 

 and long. Basal joint of the <3 forccjis-limb shorter by 



far than the 2nd joint Ephemerella {\y. 124). 



Median seta aborted. Hind wing minute and 



with scanty neuration : subcosta straight and abbrevi- 

 ated. Basal joint of the 6 forceps-limb rather longer 

 than the 2nd joint Teloganodcs {^.IM). 



Csenis Type. 



32 .... Cross-veiulets of the wing pluriserial 33 



.. .... Cross-veinlets uniserial. Median caudal seta 



long Ccenis (p. 141). 



33 .... Median seta long Tricorythus (p. 138). 



Median seta aborted Leptolujphes (p. 140). 



Prosopistoma Type. 



34 .... Median caudal seta developed Frosoinstoma {]).14Q). 



Baetis Type. 



35 .... Hind wings small or minute 36 



Hind wings absent Cloeon (p. 179). 



36 .... Hind wing oblique, elongate, narrow, and bi- 



nerved, with usually a slender costal projection . . . Centroptllmn (p. 174). 



