1968] 
Kukalovd — Mayfly Nymphs 
323 
filament are not preserved. Dimensions: length of preserved body, 
12.6 mm; length of left forewing, 1.8 mm. 
The Permian nymphs considered above present some interesting 
and unexpected features. Most striking, of course, is the position and 
nature of attachment of the wing pads. The evidence is clear that 
in these nymphs the developing wings projected away from the thorax, 
that they were attached to the thorax only along the articular region, 
and that they were independent of each other. That this condition of 
the wing pads was not confined to the mature nymphs or transitional 
to the subimago is shown by its presence in the early instars. This 
is especially significant in view of the equally independent and even 
more lateral position of the wing pads in the Megasecoptera, described 
by Carpenter and Richardson (1968, this issue of Psyche). The indi- 
cations are that in the earliest Ephemeroptera the wings developed in 
that way, and that the position of the developing wings in Recent 
mayflies, i.e., fastened back over the thorax, is a derived one. Indeed, 
the longitudinal position of the wings might well be an adaption to 
the aquatic environment — a streamlining of the body form. 3 
The geological record of the mayfly nymphs is too meagre to show 
transitions from the oblique position to the posterior position of the 
wing pads, but the Triassic nymph which Handlirsch (1918) de- 
scribed as Mesoplectopteron longipes certainly has the wings more 
oblique than in any existing species 4 although less so than in Pro- 
tereisma. 
The presence of more posteriorly directed wing pads in one of 
the Permian nymphs (no. 6) described above (but not a protereis- 
matid) suggests that loss of the divergent nymphal wings occurred 
independently in several lines of the Ephemeroptera. 
Another interesting feature is the strong development of the costal 
brace. This is well-developed in the adult Protereismatidae but 
3 It is pertinent to point out in this connection that Dr. George Edmunds 
has informed me that the wing pads of some species of the Recent family 
Siphlonuridae, which is generally recognized as the most primitive of the 
living families of mayflies, show more divergence than those of any other 
living family and that they have a more narrow basal attachment. 
The figure of Ephemeropsis orientalis , from the Jurassic of Siberia, is 
depicted by Brauer, Redtenbacher and Ganglbauer (1889, plate 1, fig. 4) 
as having wing pads in a slightly oblique position, but the more detailed 
figures of Ephemeropsis given by Meshkova (1961) shows the wing pads 
straight back, as in Recent nymphs. Handlirsch has stated (1904) that the 
Permian nymphs, Phthartus rossicus and P. netschajevi, had slightly diver- 
gent wing pads, but he attached no evolutionary significance to their 
position. 
