1902.] 4 7 



Finally it proved that the only trustworthy distinction was a 

 small, but stable, difference in colour ; for whereas in Uitln/ia the 

 broad central yellow stripe is divided by a narrow longitudinal black 

 line ; in nchelo'ia there is no such division, the stripe being unicolorous 

 throughout. This character is based on the breeding results obtained 

 from about thirty specimens, which will probably be sufficient to 

 establish its validity. It applies, however, only to the dark form of 

 the larva, which predominates so much in this locality, that I have 

 succeeded in finding only two examples of the green form. All those 

 bred from the egg being dark. Unfortunately both of these green 

 larvse proved to be acheloia, so that T can only compare them with a 

 description of the green form of ilithyia, which I made in Natal. The 

 points of difference are as follows : - The Natal ilithyia is entirely 

 dull green, with a narrow, duplicated, pale yellow, central line ; each 

 segment has on its anterior edge three black spots, one in the middle 

 of the central line, and the others on each side of it. On the other 

 hand, the Salisbury aclteloia is dull green, with a broad central 

 greenish-white stripe, containing a slightly darker, narrow, single, 

 central line in one example, but uniform in the other ; segments with- 

 out any black spots. Owing, however, to the paucity of specimens, 

 these distinctions cannot be regarded as reliable. 



The differences which exist between the pupa 1 of the two insects, though com- 

 paratively slight, are of more importance owing to their being differences of struc- 

 ture, and not merely of coloration. In the first place the vertical cephalic projections 

 are very slightly, but yet appreciably, more prominent in ackelo'ia ; and, further, in 

 this insect the dorsal hump on the mesothorax is more distinctly carinate on its 

 anterior declivity. But the most noticeable feature is the difference in the contour 

 of the two pupre as seen from above. The dorsal, or posterior, margin of the pupal 

 wing after leaving the prominent shoulder bends strongly inwards as far as the first 

 abdominal segment, and from there it curves outwards in a bold sweep, which attains 

 its greatest width on the third segment. This outward curve is much more strongly 

 marked in ackelo'ia than in ilithyia, as the following measurements show : — 



Ilithyia. Achelo'ia. 



Length of pupa 185 mm 18-5 mm. 



Width at shoulders 60 „ 6"0 „ 



,, at 1st abdominal segment ... 4'5 „ 4"5 „ 



„ at 3rd „ „ ... 55 „ 60 „ 



There seems to be no difference in colour between the two pupre beyond a con- 

 siderable range of individual variation. In the long series of ilithyia bred by Mr. 

 Hutchinson in Natal the green type of pupa vastly predominated, there being only 

 about 5 per cent, of the brown form. My own experience was just the reverse, the 

 green form being entirely absent, though the surroundings were often such as would 

 tend to produce that colour in a fully sensitive pupa. 



