114 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



now much more prominent, longer, acute, especially those of the infi'aspiracular series, those 

 on the hack of alxlomiual segments 8 and !) (tig. -ih) and those on each side of the suranal 

 plate, including the terminal ones. The two middle ones on the eighth segment are the 

 longest, being about three times as long as thick at the base, and nearly three times as long as 

 the median one on the ninth segment, while that on each- side of the median spine is as large and 

 long as those on the side of the eighth segment. On the base of the suranal plate is a trapezoidal 

 lilack patch. 



The body is yellowish green, with faint darker green longitudinal stripes. 



/Stage IV. — Length, 1.5-25 mm. Differing Itut slightly from the previous stage. Width of 

 head, 2| mm. Prothoracic spines flatter, a little more button-like. The horns (PI. LII, tig. 4, 4-r) 

 are somewhat stouter than before; early in the stage about as long as the prothoracic segment 

 is wide, but at the end not more than half as long as the body is broad. The markings are as in 

 stage III, as also the granulations. The white stripes alternate with the dark-green ones, which 

 are ciuite distinct, the black .spines being situated partly on them. The black plates on the end 

 of the niidabdominal legs are well marked. 



/Stii(/e Valid la.sf. — Length, 43 mm. ; widtli of head, 3| mm. The four prothoracic spines 

 are flattened, smooth on top, and the four black patches are wanting. The head is cherry-red 

 brown. T-he dorsal spines on all the segments (third thoracic and 1-7 abdominal), exct^pt the 

 .second thoracic (PI. LII, tig. 4<7), are not so high as broad and shorter than those of the infraspi- 

 racular series; but those on segments 8 and 9 are over twice as long as thick at base; the two 

 median spines on the eighth segment are longer than the subdorsal one is shorter than those on 

 the side. The suranal plate (PL Llll, tig. Sc), is comparativelv smooth above, with four black 

 stout spines on each side and no dark discoloration near the base. 



The granulations on the skin of the body are coarser than in the earlier stages. Spiracles 

 black. 



This only difl'ers in coloration from the previous stage in wanting the dark patches on the 

 first thoracic segment, and the dark spot on the suranal plate, while the green lines are a little 

 fainter; but the short lateral red stripes on abdominal segments 7-0 are as distinct. 



At the end of the stage when beginning to shorten preparatory to pupation some examples 

 are gi-eener, the yellow being whiter and the green greener (Joutel). 



The fully fed caterpillar of this species may be distinguished by its pale-green body tinged 

 with whitish, and the seven darker green longitudinal stripes, while on the side of abdominal 

 segments 7-9 is a broad conspicuous cherry-red line situated lielow the spiracles, though owing 

 ■to the flattening of the body in these segments (a feature peculiar to this .sjjecies) it can lie seen 

 from above. The head is cherry-red, while the spines behind the horns are smaller than in the 

 other species of the genus inhabiting the United States. It is more nearly allied to the larva of 

 ^4. seiiator/'a than any of the other species. 



It difl'ers, however, from A. senatoria in coloration and the armature, besides being a smaller 

 larva. The four prothoracic dorsal spines are larger and better defined, those of ^4. seiuttdria 

 being nearly obsolete. The horns are a little more primitive, being slightly divided at the tip, 

 while those of A. senatoria are somewhat bulbous at the end. The spines of the segments behind 

 the horns to the 7th abdominal are slightly smaller and less stout, though of about the same 

 length; those of abdominal segments 8 and 9 are considerably slenderer, though scarcely shorter 

 than ^4. senatoria. The lateral spines are slenderer than in the species mentioned, where they arc 

 decidedly stouter and more prominent. The anal legs are less coarsely spincd than in ^4. senatoria. 



The larva* of these two species are closely- allied, and judging by them the two species probably 

 had a common origin, and since ^4. senatoria has larger, stouter spines, especialh' on the end of 

 the body, this species may be regarded as the more primitive one. judging by the freshly hatched 

 lar\a. 



Compared with the two other species, A. virginieiisis and ^4. stignia., which are also closely 

 allied, A. ruhlcimda and ^4. senatoria have a smaller head but stouter horns. The j)rothoracic 

 spines are nearly alike in all the species, but in ^1. ruhicunda and ^4. .senatnriu the dorsal spines 



