Packard.] 
554 
[Feb. 19, 
apods, 1 as we may designate them, are now more than slightly half 
as long as the body. The horn-like tubercles on the prothoracic seg- 
ment are slightly longer than in the second stage. The head and 
body are dark reddish brown above, the filamental anal legs with 
two broad pale, greenish rings. All the other abdominal legs are 
green ; the green patch extends from the under side of the first ab- 
dominal segment back over the third to eighth pair of spiracles, 
and underneath to the end of the body. 
Second stage . — Length of body 14, of stemapods, 7-8, and of 
flagella 3 mm. Sept. 11. The head is rough and warty, the small 
warts bearing fine hairs. On the front towards the vertex are four 
papilliform piliferous warts of the same size and shape as those on 
the prothoracic projections, and concolorous with the dark brown 
head. These spines are represented in the other species ( C . oc- 
cidentalis ) from the willow, onty by very minute warts, bearing long 
tapering bristles. The prothoracic segment is very wide and large ; 
the well defined cervical shield very Inroad, and ending on each side 
in a large stout tuberculated horn, bearing about twelve piliferous 
papilliform tubercles, there being a rude whorl of spines in the 
middle of the horn, the others growing out at the end. There are 
four coarse piliferous warts on the hinder edge of the cervical shield. 
Along the body are scattered coarse piliferous warts, the dorsal 
four being arranged in a trapezoid. The stemapods are coarsely 
spined (more so than in C. occidentalis ) . 
A peculiarity of the genus is the pair of very long papilliform 
paranal tubercles, situated under the supra-anal plate, and ending 
in two long, stiff*, sharp bristles. 2 The supra-anal plate is long 
1 The term “tails ” or caudal filaments is too vague for these highly modified anal legs; 
hence we propose the term stemapoda or stemapods, for those ofCerura and Hetero- 
campa. The derivation is Gr. cmjjua, filament, novs, ttoSos, leg or foot. Mr. J. Hellins 
referring to these organs in Buckler’s “ Larvae of the British Butterflies and Moths ” 
(Roy. Soc., II, 138) remarks “ but now through Dr. T. A. Chapman’s good teaching, I 
regard them as dorsal appendages, somewhat after the fashion of the anal spines of 
the larvae of the Satyridae.” This I am satisfied is an error. After repeated compari- 
sons of the filamental anal legs of Cerura with those of Heterocampa marthesia, and 
comparing these with the greatly elongated anal legs of young H. unicolor as figured 
by Popenoe, and taking into account the structures and homologies of the supra-anal 
and paranal flaps, one can scarcely doubt that those of Cerura are modified anal legs. 
2 The use of these I find explained by Mr. Beilins in his description of the larva of C. 
bifida in Buckler’s Larvae of British Butterflies and Moths, II, p. 142, as follows: “At 
the tip of the anal flap are two sharp points, and another pair underneath, which are 
used to throw the pellets of frass to a distance.” Similar dung-forks are very generally 
present in geometrid larvae; the paranal papilliform tubercles being well developed, 
though we have not seen them in use. 
