1923 ] 
A New Genus of Mayflies 
171 
in subbasal region, forming cells which are twice as high as long? 
but beyond they become widely spaced, forming cells which are 
much longer than high; subcosta in subbasal region very close 
to radius, gradually diverging from it, so that near middle of 
wing the subcosta is equally distant from costa and radius; 
radial sector with four very oblique branches, the first forking a 
little over 6 mm, from end, and including within the forks a 
supplementary longitudinal vein; the second and third branches 
of the radial sector originate close together, but the origin of the 
third, though delicate, is not obsolete; the fourth, arising about 
7.6 mm. from end of wing, starts downward at nearly a right 
angle with the sector, and then bends distad; between it and 
the sector are three supplementary veins, the first long, the two 
lower shorter; media branching about 3.7 mm. from base of 
wing, the fork very acute, and between the branches a long 
supplementary vein, and near the margin four short very delicate 
supplementary veins, two above and two below the main sup- 
plement; cubitus with main (upper) part strong, slightly curved 
subapically, emitting about five cross veins to the strongly 
arched second cubitus, then two long veins (the second forked) 
to margin, then, beyond level of end of second cubitus, a vein 
which curves distad travelling to the margin parallel with the 
first cubitus, and emitting about nine oblique veins below. 
Hind wings developed, but the details cannot be made out. 
Type the following, 
Siphlurites explanatus, sp. nov. 
Length from front of head to end of abdomen 21 mm.; 
expanse 44 mm.; length of anterior wings 21 mm., the width 
about middle 7.7 mm.; eyes to base of wings 1.7 mm., the pro- 
thoracic region short and broad (it is considerably longer in 
Ephemera howarthi.) Head and thorax brown; wings hyaline, 
with pale brown veins; a slight suggestion of mottling along 
costa 
Miocene shales of Florissant. 
Scudder described five species of Ephemerid nymphs from 
Florissant; so far as can be seen, they suggest the genera Ephe- 
