BURROWING MAYFLIES. 287 
EUTHYPLOCIA, the Flounders. 
This is a large, white-winged species, similar in aspect to Polymitarcys, but the dark, 
front border of the fore wings is more diffuse, showing a tinge of sepia or even roseate 
warmth of color, and the wing tips are hooked and so strongly corrugated lengthwise 
that the venation of the tips is difficult of examination. This is a tropical American genus 
likely to be taken only on our southern border. The type species E. hecuba Hagen is from 
Vera Cruz. 
The unidentified nymph of which I present a figure in Plate LX XIX, was collected by 
E. B. Williamson in Gualan, Guatemala. It appears to differ specifically from the un- 
identified nymph that was figured by Eaton on plate 29 of his monograph (1883-1886) ; 
however, that description was drawn froma cast skin; this, froma good alcoholic specimen. 
There are no other data accompanying these specimens. 
This nymph is remarkable for its flatness and for the extraordinary length of its tusks 
and antenne. This species may be briefly described as follows: 
Euthyplocia sp. 
Length, 29 mm.; tail, 12 mm. additional; antenne,15 mm. Color grayish brown, including the 
gills; antennal legs and sete yellow. Head and body depressed, widest across the prothorax. 
Head short and thick, depressed, wider than long, bare and shinning above, hairy about the mouth. 
Antennz very long, slender, flexuous, and bare. Mandibular tusks very long, sickle-shaped. Stout to 
near the tip when suddenly narrowed to bare brown points, hairy on both inner and outer margins, 
the outer margin and dorsal surface beset as well with brownish prickles. 
Prothorax broadly depressed with flaring parallel side margins; anterior angles more broadly 
rounded and incurved to a low, obtuse tooth at rear of head each side. Mesothorax with a low, thin, lat- 
eral lobe each side above the base of the middle leg, at front of segment, and strongly tapering rearward. 
Legs strong, thickly fringed with hairs in all exposed lateral margins, femora flattened and marked 
above with scarlike, longitudinal, bare areas. Fore tibia longer than its femur and prolonged still further 
by along, straight spine that lies closely beneath the tarsus for more than half its length. Tarsus similarly 
prolonged in a spur beneath the short, tapering claw. Middle and hind legs smaller, with only short 
apical prolongation of tibie. Wing cases uniformly purplish brown. 
Abdomen long, depressed, slowly tapering posteriorly, bordered by the wide fringe of the extended 
gills. A pale middorsal line emerges conspicuously on the posterior segments. The lateral margins also 
are pale, and there are obscure, paired, pale dots in the brown of the sides. Gills on segment 1 erect, 
simple rudiments; on segments 2 to 7 double, long, flattened, and copiously fringed with filaments. Tails 
very long, flexuous, and nearly bare. 
POTAMANTHUS, the Spinners. 
This genus includes the smallest and daintiest of our Ephemerine. They are white, 
faintly tinged with yellow in one species, P. flaveola Walsh, and with green in the male of 
the other, P. diaphanus Needham. They have an expanse of wings of something less 
than an inch, with white tails of the same length. There are minute fuscous markings on 
the tips of the segments of the fore legs of the male and on the middle cross veins of the 
fore wings of the female of P. flaveola that are entirely wanting in P. diaphanus. Only 
these two American species are known. ; 
The former (Pl. LX XX) is the species occurring in the Mississippi River. I have 
specimens of it also from Lansing, Mich., and from Ithaca, N.Y. Miss Morgan (1913) has 
published an excellent figure of the nymph, copied herewith on Plate LX XX] as figure 56. 
She says that ‘“‘in Fall Creek Potamanthus crawls upon silt-covered stones and muddy 
bottoms.’’ Eaton (1883-1886) says of the European P. luteus: ‘‘The nymph harbors 
