ACADEMY OP SCIENCES. 



129 



differences in the larvae, I subjoin, in parallel columns, the description of 

 both: 



Hal. Agassizii. 



Head, body and prolegs, entirely 

 black. Abdominal legs, dirty yellow. 

 Body, slightly depressed, with the 

 three anterior and three posterior 

 segments evenly clothed with velvety 

 black hairs, out of which spring some 

 pencils of white hairs, much longer 

 than the general clothing of the body. 

 The middle segments are clothed with 

 very bright lemon yellow hairs, with 

 a black lozenge-shaped patch in the 

 middle of each segment. In some 

 specimens the yellow extends further, 

 both anteriorly and posteriorly, the 

 black hairs being consequently less; 

 but there is little or no change during 

 the growth of the larva, save in .size, 

 the colors being quite similar through 

 the successive moults. 



Hal. Agassizii. Var. Alni. Hy. Edw. 



Color of body, cream white, except 

 the head, which is jet black. Bun- 

 dles of hair of the same form and 

 arrangement as in H. Agassizii, but 

 wholly of a beautiful cream white, 

 concolorous with the body of the cat- 

 erpillar. Down the middle of the 

 dorsal region, is a row of oblong, 

 bright red, almost vermillion, lozenge 

 shaped bundles of hair, wanting on 

 first, second, third and anal segments. 



Length, 1.00 inch. 



Previous to the last moult, the cat- 

 erpillars became very dull in color, 

 and the subsequent condition was 

 seen through the larval skin prior to 

 its exclusion. The appearance then 

 presented was much closer to the 

 usual form of H. Agassizii, but with 

 a few striking differences. The body 

 was now wholly slate black. Head, 

 jet black, shining. Mouth parts, 

 black, with a streak of cream color 

 above them. 2d, 3d, 4th, 5th. 9th, 

 10th, 11th, 12th and 13th segments, 

 as in H. Agassizii, clothed with jet 

 black hairs, with long white pencils 

 interspersed. The middle segments, 

 that is, the 6th, 7th and 8th, are 

 bright golden, and not lemon yellow, 

 without any black hairs whatever. 

 Thoracic legs, black; abdominal, dull 

 yellow. 



It will thus be seen that the great difference of these larval forms consists 

 in the stages previous to the last moult, the typical one being then lemon yel- 

 low, with black extremities, and black dorsal hairs, while the other is cream 

 white, with vermillion dorsal hairs. Moreover, the last moult of my new 

 variety is apparently specifically different from the normal form, the yellow 

 being a much deeper and richer tint, and the black bunches of dorsal hairs 

 being utterly wanting. It may be well to state that H. Agassizii feeds exclu- 

 sively upon willows, whereas my Shasta examples thrived equally upon wil- 

 low and alder. 



