SESIIDJE. 93 



Under side of the transparent portions of the wings bril- 

 liantly iridescent, blue and purple. In the male all the 

 dark portions of the fore wings, except the transverse spot, 

 are thickly dusted with golden yellow, but in the female the 

 costal and dorsal margins only are golden yellow, the apical 

 blotch being dark purple ; transverse spot in both sexes black. 

 Hind wings with all the margins dark purple-grey, as also 

 are all the cilia beneath. Palpi brilliant orange-red, thorax 

 and abdomen black, except that the latter is embellished 

 with a belt of orange-red of the same breadth as above. 



The abdominal belt is liable, on the upper side, to great 

 variation in colour, from orange-red to deeper red, also to 

 orange, and yellow, and even occasionally, though rarely, to 

 white. This white variety is very remarkable, and seems 

 with us to be confined to the district round Dover. It is 

 very conspicuous when flying, and the usual red or orange 

 colouring at the base of the wings is, in it, changed to creamy 

 white. 



On the wing at the end of May and in June. 



Larva of tolerably even width, but a little broader in the 

 iniddle, hardly tapering until very near the extremities. 

 Head of rather a bright, light brown, dorsal plate whitish, 

 with the middle portion light brown ; body of a smooth clear 

 white, faintly tinged with grey ; anal segment with a light 

 brown plate. In the bark of birch, feeding on the alburnum 

 or inner layer. In the trunks of trees, and the larger stems 

 of birch bushes, but especially preferring the stump or stub 

 whence the birch stem or trunk has been cut. Here it feeds 

 sometimes in numbers, and may readily be dug out. 



Full fed in May, but probably feeding for the greater part 

 of two years. 



Pupa moderately slender, with prominent antenna and 

 wing-cases, the latter slightly projecting at the points, a pro- 

 jecting ridge in front of the head, and the plate at the back 



