22 NEW YORK STATE MUSEUM 



three forked veins are followed by three typically simple veins, 

 the first, second and third anal veins, which occupy the smaller 

 area of the hind angle of the wing. There is much variability 

 in this region in the different genera, and it is highly important 

 that these three veins be certainly recognized; to do this it is 

 only necessary to count off the three longitudinal veins of the 

 cubitus — the two branches {Cu^^ and Cuo) and the bisector of the 

 cubital fork — ^back of the media, and these three will be the three 

 best developed veins remaining. In the keys the short, incon- 

 stant interpolated longitudinal veins are called intercalaries , and 

 that whether they become attached to principal veins or branches 

 or remain independent; and the irregular veins about the margin 



Fig. 3 Venation of the fore wing of E p h e m cr a 



of the wing are called veinlets. The length of the media is meas- 

 ured on vein M.^. The fore wing is meant in the key except where 

 the hind wing is specified. Fig.3 shows the unilateral forking of 

 the cubital vein and the divergence of the cubital and first anal 

 veins at base, characteristic of the subfamily Ephemerinae. 



KEY TO THE GENERA OF MAYFLIES OF NORTH AMERICA 



Imngos 

 a The cubital and first anal veins strongly divorgent at the base (fig.3). 



Venation never greatly reduced Ephemerinae 



h The fork of the median vein very deep, almost reaching the wing 

 base; two long simple intercalaries between the first and second 

 anal veins. In the hind wing the vein R5 separates from vein R, 

 close beside and therefore is little longer than the next branch of 



the radial sector C a m p s u r u s 



hh The median vein forked for not more than three fourths of its length ; 

 in the hind wing the vein R5 arises much in advance of other 

 branches of the sector, being much longer than any of them 



