BURROWING MAYFLIES. 285 
on July 26; and from many places in the Adirondacks and about Ithaca, collected by 
myself. Miss Morgan gives the date of the first appearance at Ithaca as June 14. 
Of E. guitulata the sole specimen I have seen comes from Sport Island in the Sacan- 
daga River, N. Y., and was collected by Dr. C. P. Alexander. 
I have reared the nymphs of both E. simulans and E. varia several times, and have 
been unable to find any differences between them except a slight, somewhat intangible 
and apparently not quite constant difference in the shape of the notch that divides the 
frontal prominence into two points. This notch is in E. simulans typically a complete 
half circle, while in E. varia it is somewhat more widely open and forms but a segment 
(somewhat less than half) of a larger circle. Aside from this, the following description 
will apply to either species: 
Length when grown, 18 mm.; tails, 8 mm. additional; antenne, 4.5 mm. 
Color yellowish; abdomen with a pair of longitudinal brown streaks laid on the yellow which they 
divide. 
Antenne slender, twice the length of the mandibular tusks, thinly hairy above on basal half and 
naked thereafter to slender flexuous tips. The frontal prominence ends in a sharp tooth at either side, 
the two separated by a rounded notch in front. Mandibular tusks long, slender, upcurved, brown in 
color, and nearly naked. Maxillary palpi long, slender, thinly hairy, yellow. 
Legs moderately stout and somewhat flattened and twisted, clothed with tawny yellowish hairs 
on all exposed edges. All femora oval, fore tibia moderately flattened, widened from base outward 
only to midway its length, then parallel sided with an obtuse, bristle-covered, apical angle, but with 
lo accessory apical tooth. ‘Tarsus more than twice as long as wide and more than half as long as the 
tibia. Hind tibia prolonged beside the tarsus into a forcepslike joint, which is nearly wanting on the 
more normal middle legs. 
Wing cover of the grown nymph shows a transverse series of spots, which are those of the adult 
more closely grouped. 
Gills mainly yellowish, purplish only along the main axis. On segment 1, a bifurcated rudiment; 
on segments 2 to 7, large, bushy, the two divisions of about equal size. Tails thinly margined with 
tawny hairs. 
POLYMITARCYS, the Trailers. 
These are mayflies of medium size, having broad, white wings. The fore wings bear 
a border of dull, purplish color along their entire front margin. The legs are rather short, 
except the fore legs of the male, which are very long. The tails are very long. 
There is a single known North American species, P. albus Say. An adult female 
with protruding egg masses is shown in Plate LXXVII. The nymph is shown in Plate 
LXXVIII. 
The best account of the species is that given by W. E. Howard (in Needham et al., 
1905, pp. 60-62), who studied it at Ottawa, IIl., from which account we quote a portion: 
Nymphs of P. albus are abundant in both the illinois and Fox Rivers at Ottawa. These rivers flow 
at this place over bottoms of solid sandstone, with bars of loose sand accumulated in the eddies. The 
streams are swift in the main currents, and the nymphs of this species are to be found under flat stones 
at the edge of swift water when about ready to transform. It was from two such situations that most of 
my collections were made, from which I succeeded in breeding a single specimen. I have seen the 
subimagos emerge and arise from the surface of the water in great numbers, but always just far enough 
out from the shore, so that the nymph skins were immediately swept into the current, where they disap- 
peared before they could be procured. The difficulty in collecting the skins from the natural breeding 
places is further heightened by the emergence occurring during the evening twilight. All emerge from 
the nymph skin at the surface of the water and leave the skin afloat. 
This is a midsummer species in northern Illinois. My bred specimen is dated June 22. None 
of the imagos in my collections shows an earlier date than this, but I have nymphs which are evidently 
