284 BULLETIN OF’ THE BUREAU OF FISHERIES. 
So, again, in this genus there is a single species commonly occurring in the larger 
lakes and streams; and to that species mainly the following remarks will apply. 
I have observed Ephemera. simulans during several seasons at each of two places 
on the Great Lakes—at Lake Forest, Ill., on the shore of Lake Michigan, and at “ After- 
glow,” my summer home near North Fair Haven, N. Y., on the shore of Lake Ontario. 
In both of these places the Jake bed is sandy and not muddy. In neither place have I 
seen Hexagenia at all. Ephemera is the dominant form and the sole representative of 
the group here discussed, and it is associated in its swarming with several mayflies of 
other subfamilies and with a number of exceedingly abundant caddisflies. 
The swarms of Ephemera simulans arise less suddenly than do those of Hexagenia 
and decline more steadily after a single maximum that is reached about the first week in 
July. For many days together the herbage of the shores and the trees upon the bluffs 
are thickly besprinkled with adults for more than a stone’s throw inland from the shore. 
Then, after sundown, when they rise to enter upon their nuptial flight, the air is dark- 
ened with the clouds of them that extend in an unbroken line along the margin of the 
water. At Lake Forest, with an on-shore breeze their cast skins accumulate beside 
the piers in great floating masses, acres in total area and several inches deep, each cubic 
inch of these masses representing scores of individuals. At “Afterglow” the little 
hop hornbeam trees that cling to the front of the bluff are constantly aflutter with the 
mackerels that can not find resting places without disturbing one another; and if one 
shake such a tree, a perfect cloud of them will rise in the air 
The smallest lake at which I have studied E. simulans is Walnut Lake in Michigan. 
It is there, where the numbers are not so great and where the evening swarms are less 
rough-and-tumble, that I have seen their mating flight at its best. I have described 
this (1908), p. 261) as follows: 
After sundown the beautiful mayfly, Ephemera simulans, appears in companies of males over the 
edge of the water. The flight of one of these companies is a most delightful performance to witness, 
it is so light and graceful, and appears, withal, so exhilarating. Yet it is all up and down in vertical 
lines. With upturned head each individual flies rapidly upward, mounting quickly to a height of 
10 or 15 meters; then spreading its wings out horizontally it falls upon them, with long fore legs extended 
forward and longer tails extended backward full length, rudderlike, keeping it always head to wind. 
Thus it descends, floating on the air, yet not drifting, until at the lower level of the swarm (4 or 5 meters 
above the water), it lifts its head and rises rapidly again in flight. And the whole company flying and 
falling thus, weaving up and down in vertical lines, and passing and repassing each other, create a 
scene of great animation. 
My material in this genus comes from a good many sources, none of it, however, 
from the Mississippi River, though doubtless the genus will yet be found in many places 
in that stream. 
Typical specimens of E. simulans come from Dr. C. C. Adams, collected at Portage 
Lake, Washington County, Mich., on May 30 (these bear the earliest date of all); from 
Prof. J. H. Comstock, collected on Cayuga Lake on the 1st and 6th of July; from Dr. 
C. Betten, collected at Buffalo, N. Y., on Lake Erie on the 11th of July; and from Wal- 
nut Lake, Mich., Lake Forest, Ill., and North Fair Haven, N. Y., on numerous dates in 
the fore part of July, collected by myself. 
Typical specimens of E. varia Eaton are from Three Mile Island, Lake Winnepe- 
saukee, N. H., collected by J. H. Emerton on July 10, 1906; from Lansing, Mich., col- 
lected by George D. Shafer; from Gloversville, N. Y., collected by Dr. C. P. Alexander 
