136 
allow of more than one molt, though I 
find that I formerly limited it too greatly 
in stating that it lasted only thirty-six or 
forty-eight hours. It is true that in many 
species it does not continue longer than 
two or three days after the mine becomes 
distinctly visible to the unaided eye ; but 
there is an earlier period in such cases, 
lasting three or four days, when the mine 
can only be discerned by holding the leaf 
up to the light, and examining it with a 
lens, yet even then I have not succeeded 
in finding any other molt than that 
which discloses the pupa. ‘Thus in 
NV. fuscotibiaeella Clem. I have found 
the larva when its length did not exceed 
0.85 mm., and the mine itself was only 
1.3 mm. long, and have watched it then 
for seven days more until it left the mine 
to pupate and yet have failed to find any 
indication of a molt. The mine is already 
about 19 mm. long before it becomes 
distinctly visible; but is no wider than 
the body of the larva; its total length 
when the larva quits it is about 40 mm. 
The larva is of a pale straw yellow, and 
when full-grown is about 3.2mm. The 
young larva is embedded in the yellowish 
green parenchyma and therefore is even 
more difficult of observation than the 
larva of Phyllocnistis, which lies imme- 
diately beneath the cuticle of the leaf; 
the space mined by it at night, when I 
could not observe it, shows that it had 
not molted at night. I detected no molt 
other than that which discloses the pupa. 
This species mines the leaves of various 
species of willow (Salix). It was first 
described by Dr. Clemens from captured 
specimens, and subsequently I described 
it also from captured specimens as JN. 
ciliaefuscella, suggesting that it might 
PSYCHE. 
be NV. fuscotibiaeella. Afterwards I bred 
it from willow leaves, recognized the 
identity of the species, and suggested 
that there were two other Nepticula which 
also mine willow leaves, one of which, 
unlike all other known WNepticula, mines 
the under surface. The other miner of 
the upper surface still remains unknown, 
but the miner of the under surface proves 
to be LN. fuscotibiaeella. The egg, like 
all Nepticula eggs that I have seen, is a 
dark brown roundish or oval microscopic 
speck attached to the surface of the leaf. 
When it is attached to the upper sur- 
face the larva mines in the parenchyma 
nearest to that surface, but when it is 
attached to the under surface, it mines 
nearest to that, unless it has previously 
eaten through to the upper side as it fre- 
quently does early in life. In the latter 
part of its larval life the entire parenchy- 
ma is eaten out, so that it cannot then be 
said to be a miner of either surface. 
The egg of Lithocolletis celtisella Cham. 
is deposited on the under surface of leaves 
of Celtis, but the larva early in life eats 
through to the upper surface and becomes 
a miner of that surface. With the ex- 
ception of these two species all of the 
mines that I have examined are under 
the surface to which the egg is attached, ~ 
and the larva, or imago, leaves the leaf 
through that surface. 
I have alluded above to the fact that it 
feeds at night as showing that it could 
not then have passed a molt which es- 
caped me, but this habit is not peculiar 
by any means to this species. No leaf- 
mining larva has ever been ‘‘ caught nap- 
ping” by me. If they ever sleep they do 
so either while still eating or molting or 
they take very short ‘‘ cat naps.” Ihave 
