Packard.] 
524 
[Feb. 19, 
Fourth stage .-— Length 15 mm. The larva is now reddish-brown 
all over the body, except the head, which is dull amber-green. The 
horn is retractile, and smooth, not stiff and rough as in many Sme- 
l'inthi, for which it might be mistaken. 
Mature larva . — Length 40 mm. Now all the characters of the 
larva are assumed. The body is of a peculiar pearly hue, with a 
porcelain-like polish, the head being of the same tint as the body. 
The head is smooth, not quite so wide as the prothoracic segment, 
which is much smaller than the somewhat swollen second thoracic 
segment. All the segments are slightly swollen in the middle. The 
eighth abdominal segment is swollen dorsally, and is surmounted by 
a high rather stiff well developed horn, which is not granulated, but 
somewhat annulated ; it is black, this tint extending as a black lat- 
eral line reaching below and behind the spiracle. The suranal 
plate is of peculiar shape, being long, crescentic, and bearing a small 
knob in front, the surface of the whole plate being coarsely granu- 
lated, rust-red, becoming greenish in front. The thoracic feet are 
deep amber-red. Of the abdominal feet the first four pairs are 
large and thick, conical, while the anal pair are very small, with a 
rust-red callous spot externally. On the under side of the abdom- 
inal segments is an irregular greenish median line. 
This remarkable larva recalls those of the Sphingidse, and I con- 
fess when I first saw it, I was uncertain whether to regard it as a 
Sphingid or not. The horn is slightly retractile, and thus being 
movable, must add to its efficiency as a terrifying appendage, while 
the black streak on the sides heightens the effect of the horn. The 
spiracles also are so large and conspicuous that it is possible that 
they may add to a visage not altogether prepossessing to those in- 
sects or birds which may desire to be too intimate with it. Many 
years ago, when a boy, I found this larva on the balm of G-ilead pop- 
lar, and well remember the peculiar porcelain polish and lilac tints 
of the glaucous green skin, and the prominent horn. Mr. Lintner 
(Ent. Contr., iv, 76) has given an interesting account of this cater- 
pillar which he found both on the aspen and the willow, and he also 
at first, as he says, mistook it for some Sphinx larva. He remarks 
that the pupa has “a rather long bifid anal spine.” Dr. Lintner 
thinks that this species is identical with the European dictcea , and 
such was the opinion of Professor Zeller. I have no means at pres- 
ent of confirming or disproving this view, except to say that in the 
figures of the British larva of dictcea in Buckler’s work published by 
the Bay Society (his fig. 16, PI. xxxv) the stripe is present on the 
