286 BULLETIN OF THE BUREAU OF FISHERIES. 
near to transforming which were collected the first week in June. Imagos and subimagos of the col- 
lections are scattered all through July, but August 5 shows them most abundant. At about this date 
they were observed in swarms. By the end of August they are much less numerous, and I have no col- 
lections which are as late as September. 
The subimago stage lasts 24 hours, and when the final emergence takes place the subimago alights 
on some object near the edge of the stream, where it transforms in less than a minute. The skin of the 
subimago remains attached to the bases of the sete of the imago and in this manner is carried out over the 
stream by the flying insect, where it is finally released after some minutes. 
Miss Morgan found this species in Fall Creek at Ithaca on June 20, the earliest date 
on record. I have received specimens from points on the Susquehanna River and from 
Corning on the Chemung River in southern New York, those from the latter place bearing 
date of August 20. Say found it swarming on Lake of the Woods, United States, 
Canadian boundary. 
Mr. Stringham’s single entry concerning this species is as follows: 
August 6.—Small, white mayflies have been common for at least a week or two about the river, 
though I have never seen any of themonthedam. Collected afew this evening at 6.45. In the moming 
there are many dead ones, but I never saw a live one in the day. 
His specimens bear date of August 5 and 6, and those of Mr. Schradieck from Fair- 
port, Iowa, bear the later date. So far as scattered records at present indicate, this 
species comes on slowly and reaches its maximum of swarming in early August. 
The species is probably much more widespread than present records indicate. 
Usually it is not abundant; it is pale and inconspicuous in coloration; it is quiescent in 
habits; it is crepuscular in flight; it is rarely noticed. 
The nymph does not burrow, but lies flat upon the bottom, with its legs and tusks 
and tails outspread upon the sand. It is protectively colored (see Pl. LXXVIII, 
fig. 39) and very inconspicuous. As noted before, it is an associate of Chirotenetes, and, 
like that species, its front tarsi bear two lines of long sete within, the hairs of the two 
lines diverging and extending forward when the legs are outspread. Observations are 
lacking on this species, but it seems probable that it also uses these fringes as strainers 
to gather plankton and other food out of the passing current. 
The full grown nymph may be briefly characterized as follows: 
Length, 15 mm.; tails, 7 mm. additional; antenne, 4 mm. 
Body depressed, widest across the thin, flaring, lateral margins of the prothorax, smooth. Color 
brownish, with faint marmorate markings on thorax, and a line of pale elongate spots laid upon and 
crossing the sutures between the abdominal segments; gills pale. 
Head broadly rounded. Antenne pale, bare. Mandibular tusk much shorter than the antenne, 
swollen at the base beneath the head, where clothed externally with many prickles and a few hairs, the 
tips long and slender and bare, very gently incurved. 
Prothorax widest across the front, where the thin, lateral margin is most expanded, and ends in a 
sharp angle directed forward just outside the rear of the head. 
Legs long, especially the fore legs, pale, but ringed and banded with brown and hairy along the 
edges; femora moderately flattened, twice banded; fore tibia and tarsus elongate and double fringed 
internally with long hairs; the long, straight, apical tibial spur is closely applied beneath the basal 
fourth of the tarsus, and a similar shorter spur at the tip of the tarsus is extended beside the sharply 
decurved claw. 
Abdomen depressed and with gills widely extended laterally. The gill on segment x is an erect, 
simple, hairy rudiment, on 2 to 7 double, composed of flattened tapering filaments. The lateral margins 
of the segments are rounded in front and angulate at the rear beside the gill bases. Tails rather stout 
segments ringed with short, pale bristles. 
