May, 1953 
branch of M. Actually, as good a case can 
be made for considering this vein a branch 
of R, as of M. It is not clearly joined to 
either, but sometimes appears to arise nearer 
the stem of R than of M. The poorly de- 
veloped axillary sclerites of the mayfly wing 
give no conclusive evidence either way. 
Such being the case, I have decided to follow 
Traver’s system, in which this vein is con- 
sidered to be a branch of R,, as her system 
was used consistently in The Biology of 
Mayflies (Traver 1935a). This work has 
—antenna 
fj * | 
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‘ Pay J 
WW, ‘7-7 Il Smetanotum 
middle 
leg 
wing pad bg 
/ anal Sak 
Samy foray hind leg 
coal 
eal} gills 
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Burks: THE Mayer ties oF ILLINOIS 19 
been, and is most likely to continue for 
many years to be, the standard reference 
work on North American mayflies. 
It should further be noted that the veins 
called M, and M, by Traver have been 
called Cu, and Cu, by Ulmer, MP by Till- 
yard, and branches of vein 7 by Eaton. The 
veins Cu, and Cu, of Traver’s system cor- 
respond to Ist and 2nd anal veins of Ulmer’s, 
Cu, and Cu, of Tillyard’s, and veins 8 and 
9 of Eaton’s. 
In mayfly literature, it is frequently stated 
costal 
; stigmatic’ 
margin 
/ area 
apical 
rangle 
NG er l 
oe % - Mnete 
Se IU/o,, 
Cu Ry n 
Cum MR 4 
— genital 
forceps 
- forceps 
base 
Fig. 8.—Dorsal aspect of generalized mayfly nymph, showing structures used in classification. 
Fig. 9—Generalized mayfly wings, showing principal veins and areas used in classification. 
Fig. 10.—Generalized mayfly male genitalia, showing structures used in classification: 
a, discal spines; b, subapical spines; c, apical spines; d, apicomesal spines; e, lateral spines; 
f, basal spines; g, mesal spines. 
