IMEMOmS OF THE NATIONAL ACADEMY OF SCIENCES. 161 



The protboracic plate is rather broad, liiit (jiiite sliort aiitero posteriorly, with four pililerous 

 ■warts oil the front niid lour on the hinder edjje. The piliferoiis warts on the succeeding segments 

 are large, distinct, bhii'k, and bear but a single hair. Tlie tubercles on the second ami third tho 

 racic warts are arranged in a straight trausverse row; the two dorsal ones are slightly larger than 

 those on the third thoiacic segment. On the alxloininal segments the four dorsal tubercles are :dl 

 of tiie same si/,(! and arranged in a trapezoid, which bect)mes longer, going backward to segment 7. 

 On the eighth segment there is a double large black tubercle bearing two bristles; the tubercle is 

 several times larger than any of the others, and is evidently the result of the coalescence of the 

 homologues of the two dorsal warts occurring on the segments in front. The ninth segment with 

 the four dorsal tubercles arranged in a square, with the lateral ones farther up on the back than 

 the homologous ones in front, and in a subdorsal position. The suranal plate is black brown, nearly 

 three-fourths as long as broad, bearing six marginal and two dorsal median hairs. The thoracic 

 legs are black; the abdominal legs i^ale, with an external dark chitinous plate above the planta. 



The general color of the body is glaucous green, being of the same hue as the color of the 

 underside of the aspen leaf, on which it feeds. There is a brown dorsal spot on the eighth 

 abdominal segment, on which tlie tubercle rests, while along the sides, low dowu, at the base of 

 the abdominal legs, and in corresponding places where the legs are wanting, is a row of irregular 

 reddish spots. The skin under a ^-iuch objective is seen to be studded with fine, dark, short, 

 conical seta- or granulations which are largest and thickest on the sides of and at tlie base of the 

 middle abdominal legs. The hairs over the body are glandular, slightly bulbous, and about half 

 as long as the body is thick. 



The two 'tenant hairs on the thoracic feet are knife shaped, somewhat as in Ichthijurn inchitin. 

 The planta^ of tlie abdominal legs have a much larger number of crochets than usual in larva- of 

 Stage I, as there are twenty-six of them, forming a nearly complete but broken circle, and the 

 crochets themselves are rather short and blunt. 



Stdije II. — Length, S mm. Molted August 3. The Pheosia characters are now declared, 

 owing to the transformation of the dorsal tubercle on the eighth abdominal segment into a fleshy 

 cone or low horn. The larva feeds on the edge of the hole which it eats out of the leaf, and at first 

 sight may be mistaken for a sawfly larva, owing to the dark reddish brown spots and band on 

 the sides, which resemble abdominal legs and assimilate it in appearance to the edge of the hole, 

 which turns dark after it has been eaten out by the caterpillar. 



The prothoracic shield has now disappeared. — The head slightly narrows above and is slightly 

 bilobed, smooth, and shining, a little wider than the body, which narrows a little toward tlie end; 

 it is a dark chestnut-brown on the sides, pale chestnut in front. The body is pale green above, 

 still of the same hue as the underside of the leaf. The underside is peculiar in the thoracic and 

 short, thick abdominal legs being dark livid brown; with a large chestnut-brown patch on the 

 base of each, and on the first and second abdominal segments is a dark brown blotch wlicre the 

 base of the legs would be if they were present; farther along in the space between the fourth 

 pair of legs and the anal legs is an irregular dark brown broad line extending along the side of 

 the body to the sides of the anal legs. The latter are used in creeping, but are about half as 

 large as the middle ones. 



The hump on the eighth abdominal segment is now ireU derdopcd, hif/h, conical, and flcshi/, 

 slujhthj inclined baclicard, dark at tip, and still bearing two bristles, though the dark chitinous 

 spine is obsolete; the hornlike tubercle is half as high as the segment is thick. The body behind 

 the "caudal horn" narrows rather rapidly to the end of the suranal jilate, which is larger than 

 before, but pale and of the same color as the body. 



The anal legs are used, but are about half as large as the middle ones and with much fewer 

 crochets, which are very numerous iu the middle legs, forming a nearlj' complete circle. The 

 piliferous warts in general are now very much smaller and paler than iu Stage I, being green, like 

 the body, and scarcely visible under a strong lens. The hairs are sparse, only one ai'ising from 

 a wart, and tliey are short and tine. 



In this stage the subprothoracic eversible gland was observed in an alcoholic specimen. It 

 forms a large transverse sack, bleached white by the alcohol, and conriastiug with the red sidn 

 of the side of the segment. It sends off two lateral si])hon-like long and slender finger-shaped 

 S. Mis. ."iO 11 



